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Irrigation with treated wastewater containing nanobubbles to aerate soils and reduce nitrous oxide emissions
Abstract
The objective of the present study was to examine whether we could improve the aeration of clayey soils that had been degraded by long-term irrigation with treated wastewater (TWW) through drip irrigation with TWW aerated with oxygen (O 2) nanobubbles (ONB). A lysimeter setup was irrigated using surface and subsurface drip systems, and the effects of those systems on soil oxygen concentration, nitrogen transformations, nitrous oxide (N 2 O) emissions, and crop yield were investigated. In the surface drip system, irrigation with ONB-aerated TWW increased soil oxygen concentrations from 15.6% to 19.7% (p ¼ 0.0001). In the subsurface drip system, soil oxygen concentrations increased from 18.2% to 19.2% (p ¼ 0.0266). In all treatments, nitrate was the dominant N form in the root zone porewater (soil solution) and leachates. Nitrite concentrations were low in all treatments (<4 mg L À1), yet a clear daily accumulation pattern (from~0.05 to~1.0 mg L À1) was observed in the ONB-aerated treatments. Irrigation with ONB-aerated TWW reduced cumulative N 2 O emissions by 37% in the surface irrigation system and 14% in the subsurface irrigation system. Our results imply that irrigation with ONB-aerated TWW may be an effective way to improve soil aeration, especially in clayey soils that have been degraded by prolonged irrigation with TWW. Such practices may reduce N 2 O production and the overall N leakiness of agricultural activity.
... However, tomato cropping systems are susceptible to rhizosphere hypoxia stress due to intensive tillage, short crop rotations, and mechanical compaction practices that reduce soil quality and crop productivity in the long term (Du et al., 2020;Jiang et al., 2019). Increased aeration in the rhizosphere can improve soil fertility (Baram et al., 2021). Aerated drip irrigation (ADI) is a technique that uses micro-bubbles to deliver oxygen-enhanced water to the root zones of plants, improving aeration and soil oxygen concentrations (Lei et al., 2017;Niu et al., 2021). ...
... Microorganisms play a crucial role in regulating ecosystem function and soil biogeochemistry, which are sensitive to variations in their surroundings, including climate (De Vries et al., 2018;Shigyo et al., 2019), agronomic nutrient supplements Lekberg et al., 2021), and irrigation practices (Baram et al., 2021). Microbial community diversity and composition are affected by oxygen content (Biggs-Weber et al., 2020). ...
... The soil oxygen concentration affects the phylogenetic and physiological composition of microbial communities (Baram et al., 2021;Glass and Rico-Ramírez, 2022). Accumulating evidence suggests that soil disturbance by agricultural practices such as straw returning (Muhammad et al., 2021), conservation tillage , biochar , and organic fertilizer additions increases soil aeration and oxygen concentrations, altering soil bacterial and fungal community composition. ...
Soil bacteria and fungi play key roles in organic matter decomposition and nutrient turnover. Aerated drip irrigation (ADI) is beneficial for improving soil nutrients but its effects on bacterial and fungal communities are less known. In this study, a two-season ADI field experiment comprising three dissolved oxygen concentrations (10, 15, and 20 mg·L–1, referred to as A1, A2, and A3) and a control treatment (groundwater without aerated, CK) was conducted in a tomato plantation in Shandong, China. Soil bacterial and fungal communities were examined using high-throughput sequencing targeting 16 S rRNA and ITS genes, respectively. The ADI treatments increased fungal community diversity but did not significantly affect bacterial community diversity. However, bacterial communities were more connected within the module, with more stable network structures in the ADI treatments. In contrast, fungal networks had lower modularity values and a significant negative correlation with soil available phosphorus (AP). The ADI treatments increased the bacterial phylum Gemmatimonadetes and Firmicutes and a few aerobic taxa and strongly enriched the fungal phylum Mortierellomycota and phosphorus-dissolving taxa (Humicola, Mycothermus, and Myceliophthora). In addition, the A2 treatment enhanced functional groups related to carbon and phosphorus cycling while decreasing Plant Pathogen functional groups. The most important environmental factors affecting bacterial and fungal communities were soil organic carbon (SOC) and AP, respectively. Structural equation modeling (SEM) demonstrated that ADI directly affected soil bacterial and fungal communities and indirectly promoted SOC, AP content, and tomato yield. Overall, our findings highlight the importance of bacterial and fungal taxonomic communities, co-occurrence networks, and functions related to regulating soil carbon and phosphorus availability, providing novel evidence for the application of ADI to improve soil fertility and crop productivity.
... Despite the growing volume of literature on the benefits of irrigation with NB-water, we did not find studies that investigated the effects of irrigation with nanobubbles aerated TWW by DI and SDI on soil aeration. One exception is a recent study by Baram et al. (2021), where DI and SDI with ONB-TWW of clayey soil that had been degraded by long-term irrigation with treated wastewater was reported to improve oxygen availability and crop yield, concomitantly reducing nitrous oxide (N 2 O) emissions. ...
... The present manuscript expands the work of Baram et al. (2021) to discuss the effects of irrigation with nanobubbles aerated TWW by DI and SDI on the physiological parameters of crops. It was hypothesized that DI and SDI with TWW oxygenated by oxygen nanobubbles (ONB-TWW) could promote oxygen availability in the rhizosphere, and improve the physiological status of the plant and yield of lettuce regardless of the soil texture and origin. ...
... This system had twenty high-density polyethylene (HDPE) barrels (31.5 cm in diameter, 21 cm high, volume of 16 L) that were filled with 18 cm of Vertisol (only topsoil: 0-20 cm) compacted to field conditions (i.e., bulk densities of 1.1-1.15 g cm − 3 at a water content of 34 cm 3 cm − 3 ; Baram et al., 2021) (Table 1; Fig. 1A). The second lysimeter system used well-aerated non-degraded soil. ...
Long-term drip irrigation with treated wastewater (TWW) is known to enhance oxygen deficiency (hypoxia), especially in fine-textured soils. Hypoxia conditions around plant roots negatively affect growth and yield. Experiments were conducted to evaluate the response of lettuce grown in well-aerated (sandy) and poorly aerated (clayey) soils to surface and subsurface drip irrigation with nanobubbles oxygenated TWW (ONB-TWW). Oxygen mass balances show that irrigation with ONB-TWW supplied about 1% of the daily O-CO 2 emissions. Nevertheless , our results show that both surface and subsurface drip irrigation with ONB-TWW increased the lettuce yield regardless of the soil type or the amount of oxygen added to the soil out of the daily oxygen consumption in it. Irrigation with ONB-TWW significantly reduced membrane leakage and osmotic potential in the roots and leaves in both well-aerated and poorly aerated soils, concomitantly improving root viability and chlorophyll content in the leaves of the plants grown in the poorly aerated clayey soil. The results suggest that drip irrigation with ONB-TWW, should be considered as a viable method to improve oxygen availability in soils and to alleviate soil hypoxia. Further study is needed to elucidate the mechanisms by which ONB promote plant health and growth.
... These results indicate that micro-nano bubble water drip irrigation not only improved the root growth environment of maize but also enhanced photosynthetic efficiency, thereby boosting overall crop performance. This finding aligns with previous research, which suggests that micro-nano bubble water drip irrigation effectively promotes plant growth by improving soil aeration and phosphorus (P) availability [17,39,42,43]. The improved oxygen supply in the soil enhances root vitality, leading to better absorption of water and nutrients and subsequently increasing overall biomass [5,13,40]. ...
... Micro-nano bubble water drip irrigation increases soil oxygen content, which promotes aerobic respiration in plant roots and enhances soil enzyme activity. These changes ultimately lead to a significant increase in crop yield [17,20,39,40,42]. This positive effect has been validated in maize [47], rice [48], and vegetables [17]. ...
This study aimed to explore the combined effects of micro-nano bubble water drip irrigation and different phosphorus (P) application rates (P0: 0 kg·hm−2; P1: 86 kg·hm−2; P2: 172 kg·hm−2; P3: 258 kg·hm−2) on maize growth, soil phosphorus dynamics, and phosphorus use efficiency to optimize irrigation and P fertilizer use efficiency. Through a field column experiment, the impact of micro-nano bubble water drip irrigation on maize plant height, stem diameter, leaf SPAD values, biomass, and yield was evaluated. The results showed that (1) irrigation methods significantly affected maize growth indicators such as plant height, stem diameter, and root dry weight. Micro-nano bubble water drip irrigation consistently promoted growth during all growth stages, especially under higher P application. (2) P application significantly increased the dry weight and P concentration in maize roots, stems, leaves, ears, and grains. Under micro-nano bubble water drip irrigation, the P concentrations in roots and grains increased by 59.28% to 92.59%. (3) Micro-nano bubble water drip irrigation significantly enhanced P uptake efficiency, partial factor productivity of P, and agronomic P use efficiency. Particularly under P1 and P2 treatments, the increases were 134.91% and 45.42%, respectively. Although the effect on apparent P recovery efficiency was relatively small, micro-nano bubble water drip irrigation still improved P utilization under moderate P levels. (4) Structural equation modeling indicated that P supply under micro-nano bubble water drip irrigation primarily regulated alkaline protease and alkaline phosphatase, enhancing soil P availability, which in turn promoted maize P accumulation and increased yield. In conclusion, this study demonstrated that the combination of micro-nano bubble water drip irrigation and appropriate P application can effectively promote maize growth and nutrient utilization, providing a theoretical basis for optimizing irrigation and fertilization strategies in maize production.
... Studies show that aeration irrigation can reduce N 2 O emissions and nitrogen loss [3,18]. Through surface and underground aerated drip irrigation, N 2 O cumulative emissions can be reduced by 37% and 14%, respectively, thereby reducing nitrogen fertilizer losses [19]. However, the effect of soil oxygen content on rice stem lodging resistance has been rarely studied. ...
... This improvement in dissolved oxygen concentration benefits rice yields by increasing oxygen levels. Additionally, Baram et al. [19] observed that micro-nano aeration drip irrigation effectively enhances soil aeration, particularly in clay soils irrigated with wastewater over extended periods. Studies have shown that the APAC can significantly increase rice yields. ...
Global climate change and persistent droughts lead to soil desertification, posing significant challenges to food security. Desertified lands, characterized by high permeability, struggle to retain water, thereby hindering ecological restoration. Sand, a natural resource abundant in deserts, inspired our proposal to design hydrophobic sand and construct Air-permeable Aquicludes (APAC) using this material. This approach aims to address issues related to the ecological restoration of desertified lands, food security, and the utilization of sand resources. Reclamation of desertified land and sandy areas can simultaneously address ecological restoration and ensure food security, with soil reconstruction being a critical step. This study investigated the effects of constructing an Air-permeable Aquiclude (APAC) using hydrophobic sand on rice yield and lodging resistance, using clay aquitard (CAT) and plastic aquiclude (PAC) as control groups. The APAC enhanced soil oxygen content, increased internode strength, and improved vascular bundle density, substantially reducing the lodging index and increasing yield. This research finds that the APAC (a) increased internode outer diameter, wall thickness, fresh weight, and filling degree; (b) enhanced the vascular bundle area by 11.11% to 27.66% and increased density; (c) reduced the lodging index by 37.54% to 36.93% (p < 0.01); and (d) increased yield to 8.09 t·hm−2, a rise of 12.05% to 14.59% (p < 0.05), showing a negative correlation with lodging index. These findings suggest that APAC has very good potential for desertified land reclamation and food security. In conclusion, the incorporation of hydrophobic sand in APAC construction considerably strengthens rice stem lodging resistance and increases yield, demonstrating considerable application potential for the reclamation of desertified and sandy land and ensuring food security.
... The effect of AI on soil aeration and root morphology on crop yield was relatively complex. Simple correlation analysis and path analysis are often used to resolve the inter-relationship between crop yield and the related indicators in the soil-crop system under AI, which limited the deepening acquisition of factor-to-factor correlation analysis [17][18][19]. The influencing factors include multiple indicators of different categories with various criteria, while the evaluation depth of a single indicator was limited [20]. ...
... The effect of AI on soil aeration and root morphology on crop yield was relatively complex. Simple correlation analysis and path analysis are often used to resolve the inter-relationship between crop yield and the related indicators in the soilcrop system under AI, which limited the deepening acquisition of factor-to-factor correlation analysis [17][18][19]. The influencing factors include multiple indicators of different categories with various criteria, while the evaluation depth of a single indicator was limited [20]. ...
Soil compaction easily causes root hypoxia stress, resulting in poor root growth and the absorption of soil water and nutrients. We hypothesized that aerated irrigation (AI) could enhance nutrient uptake and utilization, thus unlocking the high yield potential by increasing soil aeration and root morphology indicators compared with that in the non-aeration treatment. A greenhouse experiment was conducted to investigate the effect of soil aeration and root morphology on the yield of greenhouse cucumbers. The dissolved oxygen (DO) in irrigation water at 10 mg L−1 (A1), 20 mg L−1 (A2), and non-aeration treatment (A0) were applied via a subsurface drip irrigation system. The soil respiration rates, DO in soil water, root morphology, and crop yield was measured. The results showed that AI could significantly improve the soil respiration rate, DO in soil water, and root morphology compared with non-aeration treatment. The A2 significantly increased soil respiration rate by 11.63% and 11.93%, respectively, compared with the A1 and A0 treatments. Under A1 and A2, the DO in soil water increased by 20.01% and 18.02%, respectively, compared with the A0. Moreover, during the flowering and fruit set, the mature, and the late stages, the root surface area, root volume, root tip number, root forks, and root dry weight in the A2 treatment significantly increased than that in the A0 treatment. The soil respiration rate, DO in soil water, root length, and root forks were the main indexes correlated to the yield, respectively. The DO in soil water and root forks number significantly influenced the yield. The cucumber yield and economic benefits in A2 peaked at 53.04 t ha−1 and 3.95 × 104 USD ha−1, increased by 7.86% and 7.30% compared with that in the A0 treatment, respectively (p < 0.05). The results could provide technical support and scientific knowledge for regulating greenhouse cucumbers under AI.
... A recent study used, a lysimeter set-up and OMNBs aerated wastewater to oxygenate the paddy soil and reduce N 2 O emission for improved crop yield (Baram et al., 2021). In all OMNBs treated soil samples, the oxygen concentration was increased from 16% to 20%, while nitrate concentration remained high compared with nitrites throughout the experiment. ...
... Overall OMNBs reduced cumulative N 2 O emissions by 37% in the surface irrigation system and 14% in the subsurface irrigation system. Current findings suggest that OMNB aerated water can improve the soil fertility of agricultural land degraded by prolonged irrigation from treated wastewater (Baram et al., 2021;Wang et al., 2021). Therefore, anoxia mediated N 2 O emission can be controlled from the lake or river sediments by OMNB application (Fig. 4). ...
Sediment hypoxia is a growing problem and has negative ecological impacts on the aquatic ecosystem. Hypoxia can disturb the biodiversity and biogeochemical cycles of both phosphorus (P) and nitrogen (N) in water columns and sediments. Anthropogenic eutrophication and internal nutrient release from lakebed sediment accelerate hypoxia to form a dead zone. Thus, sediment hypoxia mitigation is necessary for ecological restoration and sustainable development. Conventional aeration practices to control sediment hypoxia, are not effective due to high cost, sediment disturbance and less sustainability. Owing to high solubility and stability, micro-nanobubbles (MNBs) offer several advantages over conventional water and wastewater treatment practices. Clay loaded oxygen micro-nanobubbles (OMNBs) can be delivered into deep water sediment by gravity and settling. Nano-bubble technology provides a promising route for cost-effective oxygen delivery in large natural water systems. OMNBs also have the immense potential to manipulate biochemical pathways and microbial processes for remediating sediment pollution in natural waters. This review article aims to analyze recent trends employing OMNBs loaded materials to mitigate sediment hypoxia and subsequent pollution. The first part of the review highlights various minerals/materials used for the delivery of OMNBs into benthic sediments of freshwater bodies. Release of OMNBs at hypoxic sediment water interphase (SWI) can provide significant dissolved oxygen (DO) to remediate hypoxia induced sediment pollution Second part of the manuscript unveils the impacts of OMNBs on sediment pollutants (e.g., methylmercury, arsenic, and greenhouse gases) remediation and microbial processes for improved biogeochemical cycles. The review article will facilitate environmental engineers and ecologists to control sediment pollution along with ecological restoration.
... Similar studies have used air-injected SDI in greenhouse settings. It was reported that using aerated wastewater improved the aeration of clayey soils, reduced N 2 O production, and increased the aboveground biomass yield of lettuce (Baram et al. 2021(Baram et al. , 2022. D' Alessio et al. (2020) investigated the impact of air-injected water containing PPCPs on plant uptake and observed an enhanced removal of PPCPs in the air injection treatment. ...
... This was possibly due to increased soil respiration due to rising soil temperature and possibly higher microbial activities in the morning (Chen et al. 2011). Baram et al. (2021), in which soil oxygen concentration increased significantly in O treatment (19.2%) compared to NO treatment (18.2%), and Baram et al. (2022), in which the average soil oxygen concentrations significantly increased in O treatment (19.2%) compared to NO treatment (18.9%) in sandy soils, and O treatment (19%) compared to NO treatment (18%) in clayey soils. ...
As a state with the most irrigated agricultural land in the United States, Nebraska relies on freshwater resources for its irrigation. In addition to these conventional water sources, using nonconventional alternatives for crop production can be important during water shortage times. In this research, effluent from a feedlot lagoon was used as an irrigation water source at a subsurface drip irrigation (SDI) system for corn (C) and sugar beet (SB) production in western Nebraska during the 2019 and 2021 growing seasons. The objective of this study was to evaluate the effect of air injection on C and SB yield when using feedlot runoff as an irrigation source in a SDI system. Results indicated that air injection treatment (O), compared to noninjection treatment (NO), increased corn yield by 5.50% in the 2019 growing season, yet differences were not significant. During the 2021 growing season, O significantly increased corn yield by 9.17% (p ¼ 0.04). Differences in irrigation water productivity (IWP) of NO (14.19 AE 1.90 kg ha −1 mm −1) and O (14.86 AE 1.79 kg ha −1 mm −1) were not significant during the 2019 growing season while significant differences in IWP of NO (22.61 AE 5.88 kg ha −1 mm −1) and O (24.68 AE 4.55 kg ha −1 mm −1) were observed during the 2021 growing season (p ¼ 0.004). In sugar beets, no significant difference was observed in crop yield or sucrose yield between O and NO during both growing seasons. Differences in IWP were not significant during the 2019 growing season (NO: 0.10 AE 0.02 kg ha −1 mm −1 , O: 0.10 AE 0.03 kg ha −1 mm −1) and 2021 growing season (NO: 0.10 AE 0.04 kg ha −1 mm −1 , O: 0.09 AE 0.02 kg ha −1 mm −1).
... Previous studies showed that root zone aeration increased OCC (Ben-Noah and Friedman 2016; Bhattarai et al. 2006;Ouyang et al. 2021). Baram et al. (2021) found that applying aeration with oxygen Nano bubbles increased soil OCC. Zhu et al. (2019) proved that aerated irrigation treatment significantly increased OCC. ...
Aims
The stability of soil organic matter (SOM) is influenced by its chemical structure as well as by biological and environmental factors. However, the specific mechanisms by which pore space gaseous O2/CO2 concentrations affect SOM are not well understood.
Methods
The experimental design involved a 2 (Chinese photinia planted and bare land) × 2 (O2 aeration levels) × 2 (CO2 aeration levels) design compared to 2 non-aeration treatments, to investigate the impact of pore space O2/CO2 concentration on soil enzymes, soil organic carbon (SOC), light fraction organic carbon (LFOC), dissolved organic carbon (DOC) and microbial carbon (MBC).
Results
The injection of 21% O2 led to a significant increase in the activities of catalase, urease, saccharase, invertase, and polyphenol oxidase enzymes. Significant increases in the contents of SOC, LFOC, DOC, and MBC were observed when comparing the effects of injecting 21% O2 into the soil with 15% O2, with the differences between treatments on carbon turnover rate increasing over time. Additionally, vegetation treatments were observed to increase DOC, MBC, and SOC. Changes in pore space gaseous CO2 concentration from 0.03% to 0.4% had no significant effect on soil microorganisms, soil enzymes, or SOC turnover.
Conclusions
This study demonstrates that higher concentrations of pore space gaseous O2 stimulate the activity of soil microorganisms, affecting the carbon turnover rate and its stability. These findings provide important evidence of SOC responses to variations in pore space gaseous O2.
... The concentration of dissolved oxygen in the different treatments was in line with the values reported in other studies using air or oxygen nanobubbles for water aeration [56,57]. The dissolved oxygen values when gaseous oxygen was used as internal gas in nanobubbles were approximately 4 times higher than those achieved when the tank solution was saturated with air nanobubbles and 5.5 times higher than those of irrigation water used as a control. ...
The aim of this work was to determine the effect of saturating the irrigation solution with air (MNBA) or oxygen nanobubbles (MNBO) on relevant agronomic, productive, and postharvest parameters of tomato crops (Solanum lycopersicum L.) in greenhouses. As a control, conventional management was established, without nanobubbles, under the best possible agronomic conditions used in commercial greenhouses in southeastern Spain. No significant differences were found in the
soil properties analysed or in the ionic concentration of the pore water extracted with Rhizon probes. Both MNBA and MNBO modified the root distribution and improved the N uptake efficiency and field water uptake efficiency compared to the control. MNBA had the highest harvest index. The total or marketable production was not affected, although it did increase the overall size of the fruit and the earliness with which they were produced compared to the control. MNBA significantly decreased titratable acidity and soluble solids content compared to the control in the last harvests. Both nanobubble treatments improved postharvest storage under room-temperature (20–25 ◦C) conditions.
... Soil oxygen concentration impacts the structure of the soil microbial community and nutrient cycling and transformation [34,42], Agricultural management practices to improve soil aeration have recently been increasingly applied. These include straw returning [43], soil aeration [44], organic fertilizer application [45], and biochar [46], Changing soil aeration could affect the components of the soil bacterial community. ...
Root hypoxia stress and soil nutrient turnover have been related to reduced crop productivity. Aerated drip irrigation (ADI) can effectively enhance crop productivity and yield. However, the response of the soil bacterial community to different irrigation water dissolved oxygen (DO) concentrations remains elusive due to the extreme sensitivity of microorganisms to environmental variations. We investigated the effects of aerated irrigation with different concentrations of DO on soil properties and agronomic performance of cucumber, as well as the contribution of the bacterial community. We performed experiments on cucumber cultivation in Shouguang, China, including different irrigation methods (ADI: O2–10 and O3–20 mg L−1, non-aerated groundwater: O1–5 mg L−1) and nitrogen (N) application rates: 240 and 360 kg N ha−1. ADI (particularly O2) significantly improved soil properties, root growth, cucumber yields, and irrigation water use efficiency (IWUE), and appropriate DO concentrations reduced N fertilizer application and increased crop yields. Furthermore, these changes were associated with bacterial community diversity, aerobic bacteria abundance, and consolidated bacterial population stability within the network module. Environmental factors such as soil respiration rate (Rs), DO, and NO3−-N have significant effects on bacterial communities. The FAPROTAX results demonstrated enhanced nitrification (Nitrospira) and aerobic nitrite oxidation by soil bacteria under ADI, promoting the accumulation of effective soil N and improved soil fertility and crop yield. Appropriate DO concentration is conducive to the involvement of soil bacterial communities in regulating soil properties and cucumber growth performance, which are vital for the sustainable development of facility agriculture.
... However, the impact of coupling irrigation and aeration can increase soil N 2 O emissions (Hou et al., 2016;Chen et al., 2019;Shang et al., 2020). In contrast, Baram et al. (2021) found that irrigation with nanobubble-aerated treated wastewater reduced cumulative N 2 O emissions by 37 % in the surface irrigation system and 14 % in the subsurface irrigation system. Soil microbial abundance and enzyme activities (urease, phosphatase, and catalase) increase significantly with increasing oxygen content , with remarkably higher effects in the root zone than non-root zone Zan et al., 2021). ...
Soil nitrous oxide (N 2 O) emissions are strongly affected by field practices, including irrigation and fertilization. This study investigated whether aerated drip irrigation (ADI) can enhance the soil environment, mitigate N 2 O emissions, and improve crop yields relative to conventional drip irrigation (DI). Tomato and muskmelon crops were grown in a solar greenhouse under different irrigation methods (DI and ADI) and nitrogen fertilizer rates (tomato: 0, 150, 200, and 250 kg N ha-1 ; muskmelon: 0, 150, and 225 kg N ha-1). The results showed that ADI increased soil temperature by 1.3-7.0 %, oxygen concentration by 1.9-3.2 %, and soil NH 4 + and NO 3-concentrations in the upper soil layers (0-60 cm) by 3.7-27.1 % and 3.6-51.5 % and decreased soil NH 4 + and NO 3-concentrations from 60 to 100 cm depth by 5.0-17.6 % and 1.9-18.9 %, relative to DI. However, ADI decreased soil moisture by 2.3-3.6 %. ADI also significantly increased soil microbial activity by 0.5-28.6 %. In addition, ADI and 150 kg N ha-1 significantly reduced yield-scaled N 2 O emissions (YSNE S) and emission factors (EF), increasing tomato and muskmelon yields. The results of this study suggest that ADI combined with appropriate N application rates can improve soil productivity and mitigate N 2 O emissions.
... In addition, fertilizer overuse causes soils to become rigid, reducing their oxygen content (Zhou et al., 2018). Improving soil aeration is beneficial for plant growth, water and nutrient uptake, and changes the antioxidant system of plants (Baram et al., 2021;Wolinska and Stepniewska, 2013). ...
China has the largest area of vegetable cultivation in greenhouse vegetable system in the world. However, the excessive application of irrigation and fertilizers has caused soil degradation and hardening, even leading to injury and yield loss in vegetable. Increasing soil aeration oxygen can improve crop water and nutrient uptake efficiencies. However, its effects on crop antioxidant systems are less known. Due to the sensitivity of the antioxidant system to changes in soil oxygen content, it is expected that aerated drip irrigation (ADI) delivering microbubble water to the crop rhizosphere will alter root antioxidant enzyme activities, malondialdehyde (MDA) content, and osmotic regulators in tomato plants. We conducted pot experiments under eight irrigation regimes: five aerated durations (0%, 25%, 50%, 75%, and 100%) of the subsurface drip irrigation period aerated (CK, A 25% , A 50% , A 75% , and A), with two aerated sequences (L: subsurface drip irrigation follow by aerated drip irrigation, F: aerated drip irrigation follow by subsurface drip irrigation) for the A 25% , A 50% and A 75% treatments. All treatments with ADI had an average of 7.63% higher oxygen concentration (OC) than the CK treatment at 74 d after transplanting. The principal component analysis revealed that MDA of all treatments had the greatest effect on the antioxidant system, while aerated drip irrigation reduced MDA content. Increasing aeration duration from A 25% to A 75% significantly affected antioxidant enzyme activities and root growth parameters, and the L treatment had higher values than the F treatment. The L-A 75% treatment had the highest water use efficiency , nitrogen uptake efficiency, and yield. The structural equation model demonstrated that ADI indirectly promotes tomato water and nitrogen uptake efficiencies by affecting the antioxidant system and root growth.
... Cakmakci and Sahin (2021a) concluded that wastewater application with furrow irrigation method revealed the highest heavy metal contents and salinity in soil while surface and subsurface drip methods reduced heavy metal contents and salinity significantly. Baram et al. (2021) examined whether could be improve the aeration of clayey soils that had been degraded by long-term irrigation with treated wastewater through drip irrigation with treated wastewater aerated with oxygen nanobubbles. The results indicated that irrigation with treated wastewater aerated with oxygen nanobubbles reduced cumulative N 2 O emissions by 37% in the surface irrigation system and 14% in the subsurface irrigation system. ...
In order to investigate the effect of wastewater on the soil minerals movement, irrigation water use efficiency (IWUE) and leaf nutrients uptake of medicinal-industrial-landscape Lavandula (Lavandula angustifolia L.) by two types of irrigation systems, the experiment was performed as a factorial experiment in a randomized complete block design with three replications. Experimental treatments were included quality of irrigation water (fresh water and treated wastewater) and irrigation method [surface irrigation (SI) and subsurface irrigation with permeable tubes (SSI)]. Soil samples were collected at the end of the experiment for each treatment at depths of 0–15, 15–30 and 30–60 cm to analyze Electrical Conductivity (EC), phosphorus (P), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg) and total nitrogen (N). Plots were irrigated with treated wastewater by SSI method showed fresh and dry weights of canopy higher than irrigation with fresh water by SI method. The results suggested that contrary to IWUE, water quality was more effective than irrigation system on the wet and dry weights of the canopy and leaf nutrients uptake. Based on the results, SSI method with treated wastewater increased the IWUE by 64% compared to SI method with fresh water. The highest and lowest IWUE were obtained by application of the treated wastewater (0.44 kg m⁻³) and the fresh water (0.25 kg m⁻³), respectively. The higher levels of most minerals, including N, Ca, Mg, Na, K and P, were recorded when plots were irrigated by SSI system and received treated wastewater. The subsurface irrigation created significantly higher EC, Na, Mg and Ca compared to the surface irrigation in the topsoil. The EC, K, Mg and Na of second and third soil layers that received the wastewater were less compared to the fresh water. No significant effect on soil N, P and Na was observed in all three depths of soil due to application of the wastewater for irrigation.
... The mechanism of regulating soil environment by aerated water drip irrigation and the fact that aerated water drip irrigation changes soil structure are presented [25] . Oxygenated irrigation of rice [26] , potatoes [27,28] , Komatsu [29] and irrigation with treated wastewater [30] has been studied, and Two-phase flow problems in aerated subsurface irrigation was studied [31] . ...
This study investigates the effects of varying durations of aerated irrigation, administered at a consistent frequency, on the growth of greenhouse grape seedlings and the structure of the rhizosphere soil microbial community. Using two-year-old ‘Flame Seedless’ grape seedlings as the test material, we established a control group with no aeration (CK) and three treatment groups with aeration durations of 10 min (T1), 20 min (T2), and 30 min (T3), respectively. We determined grape seedling growth under different aerating durations. Additionally, changes in the rhizosphere soil microbial community of the plants were analyzed using 16S and ITS high-throughput genome sequencing to further explore the correlation between microbial diversity and plant growth. The results revealed that: (1) Aerated irrigation significantly enhanced plant growth, with the T2 treatment yielding superior increases in plant height, above-ground dry weight, below-ground dry weight, total root length, and root volume compared to T1 and T3 treatments. (2) Aeration treatments notably elevated the Shannon and Chao1 indices of the rhizosphere soil fungal community, with the T2 treatment exhibiting the most substantial effects, and the Shannon index of the bacterial community was also significantly higher under the T2 treatment. (3) The T2 treatment significantly increased the relative abundance of beneficial aerobic bacterial genera such as Flavobacterium, Ellin6067, and Coniochaeta, while decreasing the relative abundance of detrimental fungal genera like Fusarium and Gibberella. In conclusion, a 20 min aeration duration can effectively promote grape seedling growth, enhance the diversity of rhizosphere soil microbial communities, increase beneficial aerobic microorganisms, and reduce harmful ones. This study provides a theoretical basis for optimizing aerated irrigation practices in facility grape cultivation.
High-density aquaculture and hydroponic systems are essential for sustainable food production, yet they often face persistent challenges in maintaining dissolved oxygen (DO) levels, controlling microbial activity, and optimizing nutrient cycling. This study investigates the integration of oxygen and ozone fine bubble systems as a solution to these issues, with a focus on their effects on system performance and productivity. Over a 12-week experimental period, DO levels, nutrient availability, and biological outcomes were monitored to evaluate the effectiveness of the proposed approach. The results showed that the combined oxygen and ozone fine bubble system increased fish growth rates by 52.8% and survival rates by 11.6%, while enhancing plant yield by 37.4% compared to the control group. Strong positive correlations were observed between DO levels and both fish growth (r = 0.96r = 0.96r = 0.96) and plant yield (r = 0.91r = 0.91r = 0.91), highlighting the critical role of oxygenation. Time-series data revealed stable improvements in DO levels and nutrient availability in the fine bubble system, with significant reductions in ammonia accumulation. These findings underscore the importance of precise oxygenation and microbial control in high-density systems. This study provides robust evidence for the practical application of fine bubble technologies in improving both ecological sustainability and economic efficiency. By addressing key limitations in current aquaculture and hydroponic systems, the research offers a pathway for scaling these technologies to meet the demands of modern food production.
The deterioration of the soil water–air environment due to salinization can reduce soil bacterial activity and cause crop yield reduction. Micronanobubble oxygenated drip irrigation can significantly improve the nonsaline soil water–air environment and enhance bacterial activity, but its effect on salinized soil bacteria is unknown. In this study, we used a tomato cultivation experiment in mildly saline soil to evaluate the responses of the rhizosphere bacterial community to the soil microenvironment created by micronanobubble oxygenated drip irrigation. The results indicated that the soil environmental factors (including soil electrical conductivity, i.e., EC) ( r = 0.46) and root length ( r = −0.86) had important regulatory effects on bacterial community function, which had significant direct effects on tomato yield ( r = 0.46). The moderate dissolved oxygen concentration treatment significantly reduced the EC by 63.22%–73.32% compared with CK (noncultivated soil treatment) and generally increased the root length; however, only the combination of a moderate dissolved oxygen concentration and excess irrigation (A 15 W 1.2 ) significantly increased tomato yields by 190.90% compared with A 0 W 0.8 (the combination of a low dissolved oxygen concentration and insufficient irrigation) because the irrigation water volume was the limiting condition affecting the benefits of the root length increase. The high dissolved oxygen concentration treatment significantly reduced the EC by 60.36%–92.31% and increased the bacterial community diversity by 4.08%–6.16% compared with CK; these aforementioned changes favored the increase in tomato yield. However, similar to the result of the moderate dissolved oxygen treatments, the tomato yields were significantly higher and among the highest of all treatments only when a high dissolved oxygen concentration was combined with sufficient irrigation or excess irrigation (A 30 W 1 or A 30 W 1.2 ) due to the limiting effect of the irrigation water volume. Therefore, accounting for the changes in EC, soil bacterial community, and tomato yields, A 15 W 1.2 , A 30 W 1 , and A 30 W 1.2 are recommended for tomato production in mildly saline soils.
Nanobubbles (NBs) in water have been proven to improve plant growth and seed germination, potentially reducing both water and fertilizer consumption. To unravel the promotion mechanism of NBs on plant growth, this study investigated the characterization of NBs in tap water and their impacts on tomato's early growth, soil chemical properties, enzymatic activity and electrochemical properties of plant roots. Oxygen NBs (ONB) were found to increase the seed germination by 10 % and plant growth by 30 %-50 % (e.g., stem and diameter), whereas nitrogen NB (NNB) only had a significant promotion (7 %-34 %) on plant height. Additionally, compared to control group, irrigation with ONB increased the peroxidase activities by 500 %-1000 % in tomato leaves, which may increase the expression of genes for peroxidase and promote cell proliferation and plant growth. Moreover, electrical impedance spectroscopy (EIS) revealed that the ONBs could reduce the interfacial impedance due to the increased active surface area and electrical conductivity of root.
Aerated subsurface drip irrigation (ASDI) has been considered an effective method to unlock the growth potential of crops. An experiment was undertaken to monitor the effects of three aeration rates (40% aeration rate, 15% aeration rate, CK: no-aeration) on rhizosphere soil environment and growth parameters of pepper in three soil types (YC: yellow clay, SL: silt loam, HL: heavy loam). ASDI significantly increased the soil enzyme and microbial abundance, and enhanced the soil respiration compared to the control. ASDI significantly increased the pepper yield, fruit quality, and biomass of stem and leaf. The 40% aeration rate was more beneficial to these parameters than that of 15% aeration rate in YC and SL, whereas, in HL, the 40% was less effective than 15% aeration rate. Soil type significantly affected pepper rhizosphere soil environment and the yield, quality, and biomass of stem and leaf. The benefits of ASDI in YC were better than those in SL and HL. However, aeration rate and soil type had no significant effects on the fresh/dry weight of pepper root. The recommended ASDI patterns for pepper in YC and SL were 40% aeration rates, while in HL it was the 15% aeration rate.
When crop roots are in a low oxygen environment for a long time, it will lead to a series of problems. To improve soil oxygen conditions, a method of oxygenation irrigation is increasing the dissolved oxygen (DO) concentration in irrigation water. However, its application effect in a mulched drip irrigation system is not clear. In this study, a field experiment was conducted in Xinjiang to investigate the actual effect of oxygenation irrigation in field planting. We set up mechanical oxygenation (AO), venturi oxygenation (VO), and four chemical oxygenations with different DO concentrations (CO1–4). The results showed that physical oxygenation (AO, VO) was limited by the saturated DO of irrigation water. Compared with venturi oxygenation, mechanical oxygenation could reach the saturated DO faster and had higher stability of DO concentration during single irrigation. The chemical oxygenation was not limited by the saturated DO. The maximum DO in irrigation water would also increase with the increase in the amount of oxygen enhancer, but it needed more reaction time than the physical oxygen to reach a stable state. The oxygenated water would be affected by water temperature and delivery distance in the mulched drip irrigation system, resulting in the continuous decline of DO during the irrigation process. For those oxygenated water with saturated DO under different oxygenation methods (AO, VO, and CO1), when they entered the soil, there was no significant difference in the changing trend of DO. In an irrigation process, with the increase of DO, the actual oxygenation efficiency in the soil also increased. The DO concentration of irrigation water was increased from 3.9 mg L⁻¹ to 9.1 mg L⁻¹, and 10 times of irrigation was carried out during the crop growth period, then soil oxygen could be increased by an average of 6.72∼6.89%. By increasing the DO of irrigation water, the soil oxygen condition of mulched drip irrigation can be improved. Under the condition of saturated DO, each oxygenation irrigation had no significant impact on the soil physical and chemical properties. After two years of irrigation, the chemical oxygenation using sodium percarbonate had increased the soil EC, pH, and Na⁺ content, which means slightly intensified the soil salinization.
Rhizosphere hypoxia severely inhibited plant growth, reducing the crop yield and water use efficiency (WUE) in greenhouse crops. Irrigation using nanobubbles (NBs) has been an efficient method to increase crop yield and WUE by ameliorating hypoxic conditions and promoting plant growth. However, the potential effects and mechanisms of different oxygen concentrations in water enriched in nanobubbles (NBW) remain unclear. Herein, this study examined the influence of different total oxygen concentrations (TOCs, ranged between 160 - 280 mg·L⁻¹) on tomato agronomic performance, soil fertility, and the bacterial community after a two-season of NBW irrigation. The results indicated that the tomato yield, WUE, soluble sugar, and vitamin C were significantly improved by NBs, showing the trends of rising to decrease with the corresponding oxygen concentration in irrigation water. The total C (TC), organic matter (OM), available N (AN) and K (AK) in soil tended to increase and then decrease with TOC in irrigation water. NB220 obtained the highest soil OM and AN values, and NB250 obtained the highest TC and AK values. The soil bacterial community composition gradually differentiated with increasing oxygen concentration. There were significant differences in relative abundances of Proteobacteria and Nitrospirae across the six oxygen levels. The keystones in the co-occurrence network were dependent on oxygen levels. FAPROTAX results revealed that bacterial functions of methanol oxidation, N fixation, aerobic chemoheterotrophy, and cellulolysis were more abundant in NB220 treated soils, consequently resulting in better crop yield, WUE, and soil fertility. Overall, the increased abundance of taxa participating in soil nutrient turnover contributed to improved soil fertility and crop agronomic performance. Our findings provided a significant opportunity to advance the understanding of oxygen threshold during aerated irrigation, with implications for green and efficient agricultural production.
In order to clarify the response characteristics of tillering and nitrogen (N) uptake and utilization under micro-nano bubble aeration irrigation and nitrogen fertilizer level, the nitrogen uptake and utilization characteristics, tillering and yield of early rice under different irrigation methods and nitrogen levels were investigated. The results showed that micro-nano bubble aerated irrigation and nitrogen fertilizer have substantial influence on tillering of early rice, and the effect of N fertilizer was greater than the effect of oxygen. Nitrogen accumulation increased by 6.75–10.79% in micro-nano bubble aerated irrigation treatment compared with the conventional irrigation. The application of N in treatment of micro-nano bubble aerated irrigation and 160 kg N/ha fertilizer used (W1N1) was 90% of the treatment of micro-nano bubble aerated irrigation and 180 kg N/ha fertilizer used (W1N2), while the yield decreased by only 0.31%. The study indicated that the adoption of an appropriate deficit N rate combine with micro-nano bubble aerated irrigation can be an effective means to reduce non-beneficial N consumption, achieve higher crop yield and N utilization efficiency.
The use of reclaimed water (RW) for irrigation alleviates agricultural water shortages. However, N2O emissions and N fertilizer transformations in soils irrigated with RW under different N fertilizer types and soil moisture contents are poorly understood. A 216-h laboratory incubation experiment was conducted to evaluate the effects of irrigation water types (RW and fresh water, FW), N fertilizer types (15N-labeled KNO3 and (NH4)2SO4), and soil moisture contents at 40, 60, and 90 % water-filled pore space (WFPS) on N2O emissions and N fertilizer transformations in intact soil cores. The results showed that cumulative N2O emissions ranged from 3.78 to 36.30 mg N m−2, and fertilizer-derived N2O losses accounted for 0.14–2.44 % of N fertilizers, while fertilizer-derived N residues (NO3−-N + NH4+-N) accounted for 10.16–26.95 % of N fertilizers. The N2O emissions at 40 % WFPS and fertilizer-derived N residues at 60 % WFPS in soils irrigated with RW were significantly (10.98 and 20.95 %, respectively) higher than those irrigated with FW, while fertilizer-derived N2O losses at 60 % WFPS in soils irrigated with RW were 10.26 % higher than those irrigated with FW. The N2O emissions and fertilizer-derived N2O losses in soils amended with (NH4)2SO4 at 40 and 60 % WFPS were significantly (26.61–178.84 %) larger than those amended with KNO3, while fertilizer-derived N residues in soils amended with KNO3 were significantly (41.47 %) higher than those amended with (NH4)2SO4. The N2O emissions significantly increased with increasing soil moisture content. Our results indicate that N fertilizer types and soil moisture contents are the two important factors regulating N2O emissions and N fertilizer transformations. When RW irrigation is used, controlling soil moisture contents within 41 and 60 % WFPS (the optimum is 46 % WFPS) and application of KNO3 can reduce N2O emissions and fertilizer-derived N2O losses, and correspondingly increase fertilizer-derived N residues, which can contribute to climate change mitigation.
A remarkable feature of nanobubbles (–6 m in diameter) is their long lifetime in water. Supplying oxygen-nanobubbles (NBs) to continuously flooded paddy soil may retard the development of reductive conditions, thereby reducing the emission of methane (CH4), a potent greenhouse gas, and dissolution of arsenic, an environmental load. We tested this hypothesis by performing a pot experiment and measuring redox-related variables. The NBs were introduced into control water (with properties similar to those of river water) using a commercially available generator. Rice (Oryza sativa L.) growth did not differ between plants irrigated with NB water and those irrigated with control water, but NB water significantly (p 4 emission during the rice-growing season by 21%. The amounts of iron, manganese, and arsenic that leached into the drainage water before full rice heading were also reduced by the NB water. Regardless of the water type, weekly-measured CH4 flux was linearly correlated with the leached iron concentration during the rice-growing season (r = 0.74, p mcrA copy number) in the 0–5 cm layer was significantly increased by the NB water, but we found no correlation between the mcrA copy number and the cumulative CH4 emission (r = –0.08, p = 0.85). In pots without rice plants, soil reduction was not enhanced, regardless of the water type. The results indicate that NB water reduced CH4 emission and arsenic dissolution through an oxidative shift of the redox conditions in the flooded soil. We propose the use of NB water as a tool for controlling redox conditions in flooded paddy soils.
Better understanding of process controls over nitrous oxide (N2O) production in urine-impacted 'hot spots' and fertilizer bands is needed to improve mitigation strategies and emission models. Following amendment with bovine (Bos taurus) urine (Bu) or urea (Ur), we measured inorganic N, pH, N2O, and genes associated with nitrification in two soils ('L' and 'W') having similar texture, pH, C, and C/N ratio. Solution-phase ammonia (slNH3) was also calculated accounting for non-linear ammonium (NH4(+)) sorption capacities (ASC). Soil W displayed greater nitrification rates and nitrate (NO3(-)) levels than soil L, but was more resistant to nitrite (NO2(-)) accumulation and produced two to ten times less N2O than soil L. Genes associated with NO2(-) oxidation (nxrA) increased substantially in soil W but remained static in soil L. Soil NO2(-) was strongly correlated with N2O production, and cumulative (c-) slNH3 explained 87% of the variance in c-NO2(-). Differences between soils were explained by greater slNH3 in soil L which inhibited NO2(-) oxidization leading to greater NO2(-) levels and N2O production. This is the first study to correlate the dynamics of soil slNH3, NO2(-), N2O and nitrifier genes, and the first to show how ASC can regulate NO2(-) levels and N2O production.
Root restriction has been reported to reduce fruit yield, the incidence of blossom end rot (BER) and K concentration in tomato (Lycopersicon esculentum L. 'F121') plant organs. The objectives of the present work were to study the effect of root restriction, and combination of K and Ca solution concentrations, on greenhouse tomato fruit yield, quality and cation uptake. Root restriction reduced total yield but improved fruit quality by increasing the dry matter concentration and reducing the incidence of BER. Increasing the K concentration from 5.0 to 10 mmol · L -1 reduced the marketable yield, due to increased incidence of BER. Root restriction decreased K concentration and K/Ca ratio in tomato plant organs, but had no effect on K uptake rate per unit root fresh weight. Increasing K concentration from 2.5 to 10 mmol. L -1 increased the K concentration in plant organs and K uptake rate, but reduced that of Ca. In contrast, increasing Ca concentration in the solution had no effect on K concentration in plant organs and K uptake rate. The incidence of BER correlated well with K/Ca concentration ratio in the leaves, whereas a poor correlation was obtained with K/Ca concentration ratio in ripe fruit.
The timing of fertilizer nitrogen (N) application influences the availability of NOT as a substrate for denitrification. This study examined the effect of split application of fertilizer N on N2O emissions and denitrification rate in potato (Solanum tuberosum L.) production over 2 yr. Three treatments were used: 0 or 200 kg N ha(-1) at planting, and 120 kg N ha(-1) at planting plus 80 kg N ha(-1) at final hilling. Fertilizer N application increased cumulative N2O emissions. Split fertilizer N application decreased cumulative N2O emissions in 2003, but not in 2002, compared with all fertilizer N applied at planting. A greater proportion of N2O emissions occurred between planting and hilling in 2003 (67%) compared with 2002 (17%). In 2003, the higher emissions during this period resulted from the coincidence of high soil NOT availability and increased rainfall resulting in reduced aeration. Split N application was effective in reducing N2O emissions by minimizing the supply of NOT when demand for terminal electron acceptors was high. v emissions were higher in the potato hill relative to the furrow; however, denitrification rate was higher in the furrow. Nitrate intensity (NI) expresses the exposure of the soil microbial population to NO3- and was calculated as the summation of daily soil nitrate concentration over the monitoring period. Cumulative N2O emissions were positively related to NI across year, N fertility treatment and row location. Denitrification was not related to NI, reflecting the primary role of NOT in influencing the N2O:N-2 ratio of denitrification rather than the magnitude of the overall process. Split N application was an effective strategy for reducing N2O emissions in years where there was significant rainfall during the period between planting and hilling.
Nitrogen fertilizer applied to soil is the primary source of the greenhouse gas (GHG) nitrous oxide (N2O). The assessment of N2O emissions, or net fluxes of the GHG methane (CH4), are lacking for upland, arid agricultural ecosystems worldwide. In California, where rates of application for nitrogen (N) can exceed 300 kg per hectare for N-intensive fruit and nut crops (>2 million acres), liquid N fertilizers applied through microirrigation systems (fertigation) represent the predominant method of N fertilization. Little information is available for how these concentrated and spatially discrete N solution applications influence N2O emissions and net CH4 fluxes (the sum of methanogenic and methanotrophic activity). In this study we examined soil N2O-N emissions and net CH4 fluxes for drip and stationary microsprinklers, two of the most widely used fertigation emitters, in an almond orchard where 235.5 kg N/ha were applied during the season of measurement (2009-2010). We accomplished this by modeling the spatial patterns of N2O and CH4 at the scale of meters and centimeters using simple mathematical approaches. For two applications of 33.6 kg/ha and three applications of 56.1 kg/ha targeted to the phenologic stages with highest tree N demand, the spatial patterns of N2O fluxes were similar to the emitter water distribution pattern and independent of temperature and fertilizer N form applied. Net CH4 fluxes were extremely low and there was no discernible spatial pattern, but areas kept dry (driveways between tree rows) generally consumed CH4 while it was produced in the microirrigation wet-up area. The N2O-N emissions for fertigation events at the scale of days, and over a season, were significantly higher from the drip irrigated orchard (1.6 +/- 0.7 kg N2O-N ha(-1) yr(-1)) than a microsprinkler irrigated orchard (0.6 +/- 0.3 kg N2O-N ha(-1) yr(-1)). N2O emissions and net CH4 fluxes were only significantly correlated with soil water filled pore space and not with mineral-N. The correlation was much better for N2O emissions. Our results greatly improve our ability to scale N2O production to the orchard level, and provide growers with a tool for lowering almond orchard carbon and nitrogen footprints.
A spectrophotometric procedure for determination of nitrate in water, soil extracts, and a variety of other sample types is described using one reagent solution which is easily prepared and stored. Sample and equipment requirements are minimal. Reduced chemical hazard, simplicity, and versatility represent improvements over existing methods. Limit of detection is 0.01 µg N mL (0.72 μM ) or less, depending on the matrix.
Concentrations of NO2−N in land drainage and river waters in Northern Ireland in recent years have frequently exceeded EEC guide values. Very little information exists to indicate if and when NO2− accumulates in soil solution, and whether NO2− from the soil profile is the source of NO2− in drainage and river waters. The occurrence of NO2− in the field was studied and laboratory incubation experiments carried out to determine the possible sources of NO2− in grassland soil. Field studies were carried out to determine the occurrence and spatial variability of NO2− in a grazed, grassland soil. Plots receiving either 100 or 500 kg N ha−1 yr−1 were systematically sampled in May and October 1992. Concentrations of NO2− in soil were highly variable and ranged from 0 to 2.747 μg N g−1, the data being significantly skewed to the right. Correlation matrices and stepwise multiple regression analyses showed relationships between NO2− and a number of soil variables. Nitrite appeared to be related to variables which indicated its occurrence as a result of nitrification of either fertilizer- or urine-derived NH4+. Nitrate was repeatedly correlated to NO2− concentrations, suggesting that both nitrification and nitrate reduction may be responsible for NO2− formation. Spatially, nitrite occurred at random, basic geostatics producing only one variogram, showing an increase in NO2− concentrations with an increase in distance between sampling points. There was no pattern to the distribution of NO2− with depth, indicating differences in the ratios of the rates of NO2− production and consumption. Numbers of NH3-oxidizers were consistently higher than numbers of NO2−-oxidizers, with some degree of variation between samples. The microbial aspects of NO2− formation are discussed, including partial recycling of NO2− via the NO3− pool, and possible causes of NO2− accumulation due to the inhibition of NO2−-oxidizing bacteria. Laboratory incubation studies were carried out in which measurable NO2− flushes were induced. Increasing soil pH and NH4+ concentrations produced large NO2− flushes, which peaked after about 17 days of incubation, then rapidly declined. Soil incubated with urea produced NO2−N concentrations equivalent to those encountered in the field, suggesting that NH4+ oxidation accounts for a significant proportion of NO2− formed in this soil.
Nanobubbles (<200 nm in diameter) have several unique properties such as long lifetime in liquid owing to its negatively charged surface, and its high gas solubility into the liquid owing to its high internal pressure. They are used in variety of fields including diagnostic aids and drug delivery, while there are no reports assessing their effects on the growth of lives. Nanobubbles of air or oxygen gas were generated using a nanobubble aerator (BUVITAS; Ligaric Company Limited, Osaka, Japan). Brassica campestris were cultured hydroponically for 4 weeks within air-nanobubble water or within normal water. Sweetfish (for 3 weeks) and rainbow trout (for 6 weeks) were kept either within air-nanobubble water or within normal water. Finally, 5 week-old male DBA1/J mice were bred with normal free-chaw and free-drinking either of oxygen-nanobubble water or of normal water for 12 weeks. Oxygen-nanobubble significantly increased the dissolved oxygen concentration of water as well as concentration/size of nanobubbles which were relatively stable for 70 days. Air-nanobubble water significantly promoted the height (19.1 vs. 16.7 cm; P<0.05), length of leaves (24.4 vs. 22.4 cm; P<0.01), and aerial fresh weight (27.3 vs. 20.3 g; P<0.01) of Brassica campestris compared to normal water. Total weight of sweetfish increased from 3.0 to 6.4 kg in normal water, whereas it increased from 3.0 to 10.2 kg in air-nanobubble water. In addition, total weight of rainbow trout increased from 50.0 to 129.5 kg in normal water, whereas it increased from 50.0 to 148.0 kg in air-nanobubble water. Free oral intake of oxygen-nanobubble water significantly promoted the weight (23.5 vs. 21.8 g; P<0.01) and the length (17.0 vs. 16.1 cm; P<0.001) of mice compared to that of normal water. We have demonstrated for the first time that oxygen and air-nanobubble water may be potentially effective tools for the growth of lives.
Although it is well established that soils are the dominating source for atmospheric nitrous oxide (N2O), we are still struggling to fully understand the complexity of the underlying microbial production and consumption processes and the links to biotic (e.g. inter- and intraspecies competition, food webs, plant-microbe interaction) and abiotic (e.g. soil climate, physics and chemistry) factors. Recent work shows that a better understanding of the composition and diversity of the microbial community across a variety of soils in different climates and under different land use, as well as plant-microbe interactions in the rhizosphere, may provide a key to better understand the variability of N2O fluxes at the soil-atmosphere interface. Moreover, recent insights into the regulation of the reduction of N2O to dinitrogen (N2) have increased our understanding of N2O exchange. This improved process understanding, building on the increased use of isotope tracing techniques and metagenomics, needs to go along with improvements in measurement techniques for N2O (and N2) emission in order to obtain robust field and laboratory datasets for different ecosystem types. Advances in both fields are currently used to improve process descriptions in biogeochemical models, which may eventually be used not only to test our current process understanding from the microsite to the field level, but also used as tools for up-scaling emissions to landscapes and regions and to explore feedbacks of soil N2O emissions to changes in environmental conditions, land management and land use.
The continuous increase of nitrous oxide (N2O) abundance in the atmosphere is a global concern. Multiple pathways of N2O production occur in soil, but their significance and dependence on oxygen (O2) availability and nitrogen (N) fertilizer source are poorly understood. We examined N2O and nitric oxide (NO) production under 21%, 3%, 1%, 0.5%, and 0% (vol/vol) O2 concentrations following urea or ammonium sulfate [(NH4)2SO4] additions in loam, clay loam, and sandy loam soils that also contained ample nitrate. The contribution of the ammonia (NH3) oxidation pathways (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N2O production was determined in 36-h incubations in microcosms by (15)N-(18)O isotope and NH3 oxidation inhibition (by 0.01% acetylene) methods. Nitrous oxide and NO production via NH3 oxidation pathways increased as O2 concentrations decreased from 21% to 0.5%. At low (0.5% and 3%) O2 concentrations, nitrifier denitrification contributed between 34% and 66%, and HD between 34% and 50% of total N2O production. Heterotrophic denitrification was responsible for all N2O production at 0% O2. Nitrifier denitrification was the main source of N2O production from ammonical fertilizer under low O2 concentrations with urea producing more N2O than (NH4)2SO4 additions. These findings challenge established thought attributing N2O emissions from soils with high water content to HD due to presumably low O2 availability. Our results imply that management practices that increase soil aeration, e.g., reducing compaction and enhancing soil structure, together with careful selection of fertilizer sources and/or nitrification inhibitors, could decrease N2O production in agricultural soils.
Laboratory experiments were conducted with three California agricultural soils to examine substrate and process controls over temporal variability of NO and N2O production during nitrification, and to quantify the kinetics of HNO2-mediated chemical reactions. Gross NO production rates were highly correlated (r2 = 0.93–0.97) with calculated concentrations of HNO2, which were shown to originate from autotrophic microbial oxidation of NH4 + to NO2 − Production of NO was not correlated with NH4 + or NO3–, or with the overall nitrification rate. Distinct periods of high NO2– accumulation occurred below critical pH values in each soil, apparently due to inhibition of microbial NO2– oxidation. Data suggest that even during periods of relatively low NO2– accumulation and rapid overall nitrification, HNO2-mediated reactions may have been the primary source of NO. Rate coefficients (kPNO) relating NO production to HNO2 concentrations were determined for sterile (λ-irradiated) soils, and were similar to kPNO values in 2 of 3 nonsterile soils undergoing nitrification. Production of N2O was correlated with HNO2 (r2 = 0.88–0.99) in sterile soils, and with NO2– and NO3– (R2 = 0.72–0.91) in nonsterile soils. Experiments using 15N confirmed that dissimilatory NO3– reduction contributed to N2O production even under primarily aerobic conditions. Sterile kPNO and kPN2O values were correlated (r2 = 0.90 and 0.82) with soil organic matter content. Overall, the results demonstrate that both steps of the nitrification sequence, together with abiotic reactions involving NO2–/HNO2 need to be considered in developing improved models of NO and N2O emissions from soils.
The increased use of trickle or drip irrigation is seen as one way of helping to improve the sustainability of irrigation systems around the world. However, soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper, we describe results of a simulation study designed to highlight the impacts of soil properties on water and solute transport from buried trickle emitters. The analysis addresses the influence of soil hydraulic properties, soil layering, trickle discharge rate, irrigation frequency, and timing of nutrient application on wetting patterns and solute distribution. We show that (1) trickle irrigation can improve plant water availability in medium and low permeability fine-textured soils, providing that design and management are adapted to account for their soil hydraulic properties, (2) in highly permeable coarse-textured soils, water and nutrients move quickly downwards from the emitter, making it difficult to wet the near surface zone if emitters are buried too deep, and (3) changing the fertigation strategy for highly permeable coarse-textured soils to apply nutrients at the beginning of an irrigation cycle can maintain larger amounts of nutrient near to and above the emitter, thereby making them less susceptible to leaching losses. The results demonstrate the need to account for differences in soil hydraulic properties and solute transport when designing irrigation and fertigation management strategies. Failure to do this will result in inefficient systems and lost opportunities for reducing the negative environmental impacts of irrigation.
Unwelcome Dominance
Stratospheric ozone is depleted by many different chemicals; most prominently, chlorofluorocarbons (CFCs) responsible for causing the Antarctic ozone hole. Nitrous oxide is also an ozone-depleting substance that has natural sources in addition to anthropogenic ones. Moreover, unlike CFCs, its use and emission are not regulated by the Montreal Protocol, which has helped to reverse the rate of growth of the ozone hole. Surprisingly, Ravishankara et al. (p. 123 , published online 27 August; see the Perspective by Wuebbles ) now show that nitrous oxide is the single greatest ozone-depleting substance that, if its emissions are not controlled, is expected to remain the dominant ozone-depleting substance throughout the 21st century. Reducing nitrous oxide emissions would thus enhance the rate of recovery of the ozone hole and reduce the anthropogenic forcing of climate.
NH2OH, the first intermediate in the oxidation of NH4+ to nitrite by the nitrifying bacterium, Nitrosomonas europaea, was recovered as the oxime of cyclohexanone. 15N, 18O-tracer experiments using highly enriched 15NH4Cl and 18O2 yielded oxime that was correspondingly highly enriched (greater than or equal to 92 atom %) in these isotopes. These results show that the source of NH2OH is largely or entirely NH4+, as opposed to hydrazine, which was added to inhibit the further oxidation of NH2OH to nitrite, and that NH4+ yields NH2OH by way of a monooxygenase reaction involving direct insertion of O from O2. The oxidation of NH4+ and NH2OH must be functionally linked in N. europaea, inasmuch as the reducing equivalents required by the monooxygenase to reduce the second atom of O2 to water can arise only through the concomitant oxidation of NH2OH.
To reveal the effects of coupling nitrogen (N) application and aerated irrigation on soil CO2 and N2O emission, and their relationship with soil temperature and moisture, an experiment was conducted in greenhouse melon fields by using the method of static chamber/gas chromatography to determine the CO2 and N2O emissions of different nitrogen rates under aerated irrigation. There were two irrigation factors (AI: aerated irrigation; CK: conventional irrigation) and three N levels (N1: 0; N2: 150 kg·hm-2, the traditional nitrogen application rate was 2/3; N3: 225 kg·hm-2, traditional nitrogen application rate). The results showed that soil CO2 and N2O emissions in AI treatment were higher than those in CK, but no significant difference was observed between the two irrigation methods. Under the same irrigation method, soil CO2 and N2O emission significantly increased with the increases of N application rate, indicating that N application was the main influencing factor for CO2 and N2O emissions. There were significant positive relationships between soil N2O emissions and soil temperature and water filled pore space (WFPS) under the AI treatment. Soil CO2 emission were positively correlated with soil temperature. When N application reduced to N2 rate under AI treatment, the yield was increased by 6.9% and the greenhouse warming potential was reduced from 9544.82 kg·hm-2 to 9340.72 kg·hm-2. Thus, it is feasible to reduce the amount of N fertilizer under AI treatment to mitigate greenhouse gas emission in agricultural production systems.
Significant global warming increases over the last century have resulted in recent research focused on practices to reduce greenhouse gas (GHG) emissions. Agricultural management practices, such as nitrogen (N) fertilization and aerated irrigation (AI), have significantly increased crop yields by improving soil water and fertilizer availability, and have been widely adopted in recent years. However, the interactive impact of different growing seasons and management practices in the greenhouse on GHG emissions is unclear. This greenhouse study was conducted during Spring and Autumn cultivation periods in Yangling, China with five N application rates (0, 50, 150, 200,250 kg ha ⁻¹ ) and two irrigation methods (AI and conventional irrigation [CK]). The results indicated that AI and N application both increased tomato yield, but also increased soil CO 2 and N 2 O emissions. The temperature was 4 °C higher during Spring cultivation than during Autumn cultivation, which significantly (P < 0.05) increased soil emissions of CO 2 , N 2 O, and net GHG by 10.6%, 43.8%, and 12.3%, respectively. However, the yield in Spring cultivation only increased by 5.1% (P > 0.05). Thus, among the selectable cultivation seasons, the cooler season (Autumn) along with AI and 200 kg N ha ⁻¹ , was recommended to farmers to avoid adverse effects of a warming environment. AI and 150 kg N ha ⁻¹ in Spring cultivation could be recommended as an alternative measure to local farmers. Our results suggest that in a future warmer climate, reducing nitrogen fertilizer rate in conjunction with the use of AI will remain important practices for maintaining crop yield while reducing soil net GHG emissions. There is an urgent need to transform current management practices to offset the negative impacts of climate change.
Coordination of water saving, yield and quality increase remains an attractive problem in agricultural production. Transporting irrigation water rich in micro-nano bubbles and fertilizers to the crop root zone through subsurface drip irrigation is expected to be an effective technique. In present study, cucumber and tomato cultivated in greenhouse were subjected to investigate the effects of three mixing ratios of micro-nano bubble water and groundwater combined with three different oxygation frequencies on irrigation water use efficiency, crop yield and quality. The results indicated that micro-nano bubble water oxygation could significantly increase their yield, irrigation water use efficiency and fruit quality (p < 0.05) without increasing the amounts of irrigation water and fertilizer, which demonstrated a cleaner production being friendly to soil ecological environment and sustainability using water saving technology. In the optimal treatment, the yield, irrigation water use efficiency, vitamin C, and soluble sugar of tomatoes increased by 16.9%, 16.9%, 17.7% and 39.2%, while those for cucumbers were 22.1%, 22.1%, 16.7% and 19.4%, respectively. This was mainly due to the increased soil oxygen content, longer retention time and stronger mass transfer ability of micro-nano bubbles. The recommended micro-nano bubble water oxygation mode for tomato plantation was the mixing ratio of 1:4 combined with the frequency of once every 5d, while that of cucumber being the mixing ratio of 1:0 with the same frequency with tomato. The study aims to provide a novel concept for the synergistic realization of water saving, yield increases and quality improvements in greenhouse crop production using subsurface drip irrigation.
Agricultural activity is one of the major sources of nitrous oxide (N 2 O) emission into the natural environment. Yet, due to the soil's spatial heterogeneities it is hard to accurately upscale point N 2 O emission measurements into the orchard scale. This study aims to introduce a simple, yet robust, way for upscaling point N 2 O emission measurements into the orchard scale, under drip and micro-sprinkler irrigation systems. Surface point measurements of N 2 O emissions were performed at five distances from drip and micro-sprinkler emitters in two almond orchards, following irrigation and fertigation events. Principal component analysis (PCA) and linear regression were used to study the correlations between the soil water filled pore-space (WFPS), and subsurface N 2 O, NO 3 − and NH 4 + concentrations down to depth of 60 cm. The correlation tables indicated that most of the N 2 O emission resulted from microbial nitrification in the top soil (< 10 cm). However, in many cases the correlations did not provide meaningful explanations to the relations between the subsurface parameters and the surface N 2 O emission flux. It was suggested that the main limitation of the analysis results from the current soil sampling method, where soil samples are not taken from the profile inside the collar in-order to keep the soil profile undisturbed over long measuring periods. In the microsprinkler irrigation, relative water application depth of the emitter, showed strong positive linear correlation to the soil NH 4 + concentration and surface N 2 O emission flux. These correlations could be used for upscaling the point measurements into the tree and orchard scale. In the drip irrigation, the N 2 O emission flux was found to follow the water and NH 4 + distribution pattern, and could be upscaled to the tree and orchard level using a sinusoidal function using only measurement of the peak emission and the radius of the wetting pattern. These results improve current understanding on the dynamics of N 2 O production in orchards irrigated with micro-irrigation systems in arid and semi-arid ecosystems and might contribute to modeling of N 2 O emissions using less rigorous methods.
Core Ideas
Movement of O 2 in the soil is mainly diffusive.
Respiration consists of plant root and microbial O 2 uptake, roughly of the same magnitude.
Reduced O 2 and elevated CO 2 concentrations negatively affect plant growth and productivity.
O 2 concentration, air content, and ODR are good quantifiers for O 2 availability to plant roots.
Adding bubbles or H 2 O 2 to irrigation and injecting air to soil showed mostly favorable results.
Soil aeration processes and status are reviewed with regard to different soil, climatic, land‐use, and crop types and with regard to diffusive and advective flow mechanisms. Factors affecting aeration status and its quantifiers are discussed and active soil aeration (“oxygation”) practices are presented. Movement of O 2 from the soil surface into the soil profile and its transport into soil aggregates and toward plant roots is mainly diffusive. In most circumstances, root respiration is constrained by vertical O 2 diffusion from the atmosphere to the root zone and by the diffusive resistance of the mucilage layer. Several O 2 –diffusive flow models are proposed and discussed with regard to the different geometries, relevant length scales, boundary conditions, and sinks. Soil aeration by advective O 2 flow, driven by barometric pressure changes, may also be significant in dry, coarse‐textured soils with no underlying impermeable layers. Respiration in the soil consists mainly of plant root and microbial O 2 uptake, which are roughly of the same magnitude and strongly correlated through symbiotic and competitive relationships. The bulk, areal soil respiration rate varies from several to tens of grams of O 2 per square meter per day depending on soil cover: fallow, pasture, forests, unirrigated and irrigated, cropped fields, and orchards (in general increasing order). Soil respiration rate is also affected by climatic conditions, where a temperature difference of 10°C increases O 2 consumption (and CO 2 production) two‐ to threefold. The ratio between emitted CO 2 and inspired O 2 (respiratory quotient) is not unity (on a molar basis) but rather depends on the types of respiring populations and environmental conditions. Reduced O 2 and elevated CO 2 concentrations negatively affect plant growth and productivity. These conditions are correlated mostly with wet and warm soils, such as intensively irrigated fields with fine‐textured soils (high water retention) during the summer. Oxygen‐availability quantifiers such as O 2 concentration, air content, and O 2 diffusion rate are superior to other quantifiers such as soil properties (e.g., soil texture, porosity) and redox potential. In the last few decades, several active aeration methods have been proposed and evaluated, such as adding air or O 2 bubbles or H 2 O 2 to the irrigation water and air injection into the soil. Although these methods have given mainly positive results, none is widely used in agricultural practice, due mainly to a lack of profitability potential, field‐scale proof demonstration, and a coherent protocol for field application.
Biological denitrification or dissimilatory reduction of nitrate and/or nitrite to gaseous N oxides and N2 gas has long been considered an important mechanism of N loss from soil. Since denitrification occurs only in the absence of oxygen, or at particularly low oxygen concentrations, it has been widely accepted as the cause of the poor efficiency of N use in flooded soils, where a well-developed anoxic layer is a characteristic feature (De Datta 1981). It is apparent from estimates of N loss from nonflooded plant-soil systems, that denitrification can also play an important role in N cycling in these soils. Allison (1955, 1966) and Hauck (1971) have reviewed the literature pertaining to N balance in plant-soil systems and conclude that between 10 and 30% of the applied N is commonly lost, most probably by gaseous loss mechanisms, since conditions were often not conducive to leaching. Denitrification is believed to account for most of this loss.
The challenge of meeting the projected doubling of global demand for food by 2050 is monumental. It is further exacerbated by the limited prospects for land expansion and rapidly dwindling water resources. A promising strategy for increasing crop yields per unit land requires the expansion of irrigated agriculture and the harnessing of water sources previously considered “marginal” (saline, treated effluent, and desalinated water). Such an expansion, however, must carefully consider potential long-term risks on soil hydroecological functioning. The study provides critical analyses of use of marginal water and management approaches to map out potential risks. Long-term application of treated effluent (TE) for irrigation has shown adverse impacts on soil transport properties, and introduces certain health risks due to the persistent exposure of soil biota to anthropogenic compounds (e.g., promoting antibiotic resistance). The availability of desalinated water (DS) for irrigation expands management options and improves yields while reducing irrigation amounts and salt loading into the soil. Quantitative models are used to delineate trends associated with long-term use of TE and DS considering agricultural, hydrological, and environmental aspects. The primary challenges to the sustainability of agroecosystems lies with the hazards of saline and sodic conditions, and the unintended consequences on soil hydroecological functioning. Multidisciplinary approaches that combine new scientific knowhow with legislative, economic, and societal tools are required to ensure safe and sustainable use of water resources of different qualities. The new scientific knowhow should provide quantitative models for integrating key biophysical processes with ecological interactions at appropriate spatial and temporal scales.
The increasing demand for freshwater (FW) for domestic use turns treated wastewater (WW) into an attractive source of water for irrigated agriculture. The main goal of this study was to evaluate the impact of 16 yr of irrigation with WW on the conditions that developed in the root zone of avocado trees planted on clayey soil and compare with FW use. High-resolution field sampling determined the spatial distribution of chloride, exchangeable sodium percentage, and dissolved organic content below the dripper, revealing higher salinity and sodicity, lower hydraulic conductivity, and possible preferential flow pattern linked to wettability in WW-irrigated soils. Laboratory measurements on disturbed samples showed that higher swelling pressure developed in the 20- to 40-cm and 40- to 60-cm layers of the WW-irrigated soil. Finally, continuous monitoring of oxygen concentration at the 10-, 20-, and 30-cm depths in the root zone near the trees and halfway between adjacent trees revealed that the oxygen level at the 20-cm depth was the most affected by WW irrigation. During the rainfall season, this layer could experience relatively long periods with minimal oxygen concentrations. During the irrigation season, less oxygen is available in that layer than in the FW-irrigated one. Dynamics of oxygen concentration at the 30-cm depth show a clear event of wetting and drainage in the FW-irrigated plots, while the relatively stable high oxygen level in that depth in the WW-irrigated plots might reveal nonuniform wetting, insufficient water percolation due to low hydraulic conductivity, and related low leaching efficiency of the soil profile.
Dissolved oxygen (DO) is commonly recognized as an important factor influencing nitrous oxide (N2O) production by ammonia-oxidizing bacteria (AOB). However, it has been difficult to separate the true effect of DO from that of nitrite, as DO variation often affects nitrite accumulation. The effect of DO on N2O production by an enriched nitrifying sludge, consisting of both AOB and nitrite-oxidizing bacteria (NOB), was investigated in this study. Nitrite accumulation was minimised by augmenting nitrite oxidation through the addition of an enriched NOB sludge. It was demonstrated that the specific N2O production rate increased from 0 to 1.9 ± 0.09 (n = 3) mg N2O-N/hr/g VSS with an increase of DO concentration from 0 to 3.0 mg O2/L, whereas N2O emission factor (the ratio between N2O nitrogen emitted and the ammonium nitrogen converted) decreased from 10.6 ± 1.7% (n = 3) at DO = 0.2 mg O2/L to 2.4 ± 0.1% (n = 3) at DO = 3.0 mg O2/L. The site preference measurements indicated that both the AOB denitrification and hydroxylamine (NH2OH) oxidation pathways contributed to N2O production, and DO had an important effect on the relative contributions of the two pathways. This finding is supported by analysis of the process data using an N2O model describing both pathways. As DO increased from 0.2 to 3.0 mg O2/L, the contribution of AOB denitrification decreased from 92% - 95%-66% - 73%, accompanied by a corresponding increase in the contribution by the NH2OH oxidation pathway.
The experimental evidence for the existence of nanobubbles is summarized. The paradox represented by their stability and the apparent contradiction with the Laplace-Young equation is discussed in detail. A review of surface thermodynamics is given, which shows that nanobubbles are only stable in water super-saturated with air, and also that the surface tension of the water-air interface decreases with increasing super-saturation. Computer simulation evidence for this reduction is reviewed. Experimental measurements showing the reduction in surface tension in the case of nanobubbles are given. The consequences of this novel physical phenomenon are discussed for nanobubbles, as well as more broadly.
The reuse of treated wastewater in agricultural systems could partially help alleviate water resource shortages in developing countries. Treated wastewater differs from fresh water in that it has higher concentrations of salts, Escherichia coli and presence of dissolved organic matter, and inorganic N after secondary treatment, among others. Its application could thus cause environmental consequences such as soil salinization, ammonia volatilization, and greenhouse gas emissions. In an incubation experiment, we evaluated the characteristics and effects of water-filled pore space (WFPS) and N input on the emissions of nitrous oxide (N2O) and carbon dioxide (CO2) from silt loam soil receiving treated wastewater. Irrigation with treated wastewater (vs. distilled water) significantly increased cumulative N2O emission in soil (117.97 µg N kg−1). Cumulative N2O emissions showed an exponentially increase with the increasing WFPS in unamended soil, but the maximum occurred in the added urea soil incubated at 60% WFPS. N2O emissions caused by irrigation with treated wastewater combined with urea-N fertilization did not simply add linearly, but significant interaction (P<0.05) caused lower emissions than the production of N2O from the cumulative effects of treated wastewater and fertilizer N. Moreover, a significant impact on cumulative CO2 emission was measured in soil irrigated with treated wastewater. When treated wastewater was applied, there was significant interaction between WFPS and N input on N2O emission. Hence, our results indicated that irrigation with treated wastewater should cause great concern for increasing global warming potential due to enhanced emission of N2O and CO2.
Heavy clay soils are regarded as less permeable due to their low saturated hydraulic conductivities, and are perceived as safe for the construction of unlined or soil-lined waste lagoons. Water percolation dynamics through a smectite-dominated clayey vadose zone underlying a dairy waste lagoon, waste channel and their margins was investigated using three independent vadose-zone monitoring systems. The monitoring systems, hosting 22 TDR sensors, were used for continuous measurements of the temporal variation in vadose zone water-content profiles. Results from 4years of continuous measurements showed quick rises in sediment water content following rain events and temporal wastewater overflows. The percolation pattern indicated dominance of preferential flow through a desiccation-crack network crossing the entire clay sediment layer (depth of 12m). High water-propagation velocities (0.4-23.6mh -1) were observed, indicating that the desiccation-crack network remains open and serves as a preferential flow pathway year-round, even at high sediment water content (∼0.50m 3m -3). The natural formation of desiccation-crack networks at the margins of waste lagoons induces rapid infiltration of raw waste to deep sections of the vadose zone, bypassing the sediment's most biogeochemically active parts, and jeopardizing groundwater quality.
The behavior of nitrous oxide (N2O) in fertilized soil was studied in terms of soil fluxes, the production rates at various depths and the turnover in soil.
The diffusive losses of N2O to the atmosphere calculated from soil N2O profile compared favorably with the flux directly determined with a closed chamber technique. The estimate of N2O production rates at several depths demonstrated that the sites of N2O production was only near the soil surface. The calculated residence time of N2O in the entire soil column studied was only 1.4 hour during active emission period and less than 1 day even in the later
period having trace N2O emission. The prolonged N2O emission observed after the active phase was due likely to a lasting N2O production rather than a supply from the soil N2O reservoir. The results suggested that most N2O in soil was emitted quite promptly to the atmosphere after its production. A minor role of soil as an N2O reservoir is emphasized from the viewpoint of the origin of groundwater N2O.
A nonfoaming method for semimicro Kieldahl determination of total nitrogen in plant samples containing appreciable amounts of nitrate was developed for use with a digestion block utilizing test tubes for digestion flasks. The sample (30 to 200 mg) is treated with 5 ml of a sulfuric acid:salicylie acid (30:1 ) mixture at room temperature for 1 hr. Catalyst [K2SO4:CuSeO3·2H2O:pumice 970:19:11 w/w/w)] is added and the mixture is digested at 360 to 380°C for 1 hr after the mixture clears. Ammonium in the digest is determined by a suitable method. This semimicro Kjeldahl procedure results in a 95% or better recovery of nitrate, either from KNO3 or from KNO3 added to plant material.
The most sensitive spectrophotometric procedure for the determination of ammonium is based on the conversion of ammonium into the intense blue indophenol complex (IPC) by means of salicylate and nitroprusside. Optimization of concentration, preparation and timing of the addition of reagents, reaction temperature and protection from light increased the conversion of ammonium into IPC by about 50% compared with existing methods. The absorbance was 0.60 at a concentration of 20 nmol of ammonium per millilitre of final solution (RSD of the manual procedure=0.6%; n=10) with a detection limit of 0.4 μM in samples.
We present an update of the global budget of atmospheric nitrous oxide (N2O) that accounts for recent revisions in estimates of global emissions. Most importantly, new estimates of N2O emissions from agriculture and from oceans and a surface sink of N2O have been included. Our estimates confirm that current food production is the largest anthropogenic source of N2O. However, its relative share in total anthropogenic emissions (about 60%) is smaller than in earlier studies (almost 80%). We estimate past trends in global emissions of N2O and use these as input to a simple atmospheric box model to calculate trends in atmospheric N2O concentrations for the period 1500-2006. We show that our revised estimates for global emissions of N2O are consistent with observed trends in atmospheric concentrations.
Lysimeters are used to study and monitor water, fertilizers, salts and other contaminants and are particularly valuable in transpiration and evapotranspiration research. Saturation at the soil bottom boundary in a lysimeter is inherent to its design. A drainage extension made of porous media with high hydraulic conductivity and substantial water holding capacity was devised to extend the lysimeter in order to produce soil moisture conditions mimicking those in the field. Design criteria that assure equal discharge in the soil and in the highly conductive drain (HCD) were established and formulated. Desired matric head at the lysimeter base is determined by HCD extension length. Its value can be manipulated and can range between saturation and the soil's field capacity. Conditions where the HCD is not limiting to flow are obtained through selection of the appropriate cross sectional area ratio between the soil in the lysimeter and the HCD. The validity of these criteria was confirmed with 200 l working lysimeters in the field, with and without plants, and with detailed flow tests utilizing smaller (15 l) lysimeters. Comparison of computed and measured matric head and leachate volume indicates that the proposed method can serve to maintain conditions similar to those in the field.
The optimum yield-scaled global warming potential (GWP) of perennial crops on arid land requires effective strategies for irrigation and fertilization. In 2009-2010, N2O emissions and CH4 oxidation were measured from an almond [Prunus dulcis (Mill.) D.A. Webb] production system irrigated with nitrogen (N) fertilizers. Individual plots were selected within a randomized complete block design with fertilizer treatments of urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN). Event-related N2O emissions from irrigation and fertilization were determined for seasonal periods of post-harvest, winter, spring and summer. Peak N2O emissions in summer occurred within 24 hours after fertilization, and were significantly greater from UAN compared to CAN (p < 0.001). Cumulative N2O emissions from UAN were on average higher than CAN though not significantly different. Air temperature, water-filled pore space (WFPS), soil ammonium (NH4+) and soil nitrate (NO3-) showed significant positive correlation with N2O emissions and significant negative correlation was found for the number of days after fertilization (DAF). The percentage of N2O loss from N fertilizer inputs was 0.23% for CAN and 0.35% for UAN while CH4 oxidation offset 6.0 to 9.3% of N2O emissions. Total kernel yield was not significantly different between fertilizer treatments. Yield-scaled GWP for almond from CAN (60.9 kg CO2eq Mg-1) and UAN (91.9 kg CO2eq Mg-1) represent the first report of this metric for a perennial crop. These results outline effective irrigation and fertilization strategies to optimize yield-scaled GWP for almond on arid land.
Although micro- and nano-bubble technology has been attracting attention in many fields, the state of water after the introduction of those bubbles is still not clear. In this study, the existence and stabilization of nano-bubbles after the generation of bubbles were investigated. The presence of nano-sized particles was detected through dynamic light scattering for days, when pure oxygen was used to generate the bubbles, and for less than 1 h, in the case of air bubbles. NMR spin–lattice relaxation time increased with the introduction of micro- and nano-bubbles in manganese ions solution, indicating the presence of a gas–liquid interface which adsorbed the manganese ions. Furthermore, the zeta potential measured in the water after the introduction of oxygen micro- and nano-bubbles was in the range from −45 mV to −34 mV and from −20 mV to −17 mV in water bubbled with air, indicating the presence of stable electrically charged particles. This study suggested a strong possibility of the existence of nano-bubbles in water for a long time. The stability of nano-bubbles is supported by the electrically charged liquid–gas interface, which creates repulsion forces that prevent the bubble coalescence, and by the high dissolved gas concentration in the water, which keeps a small concentration gradient between the interface and the bulk liquid.
Activated sludge from a domestic sewage works was enriched with nitrifying bacteria by running a laboratory fermenter on ammonia-supplemented sewage. This enriched culture was used to determine respirometrically the kinetics of microbial nitrification. It was demonstrated that the reaction fits the Michaelis-Menten model for temperatures from 10 to 35°C, having a temperature optimum at 15°C (K3 0.72 mg 1−1 NH3). Nitrification is unaffected by high dissolved oxygen concentration 38 mg 1−1 O2 at 30°C) after acclimatisation. Nitrite concentrations > 20 mg 1−1 are inhibitory to the reaction.
Microirrigation with fertigation provides an effective and cost-efficient way to supply water and nutrients to crops. However, less-than-optimum management of microirrigation systems may cause inefficient water and nutrient use, thereby diminishing expected yield benefits and contributing to ground water pollution if water and nitrogen applications are excessive. The quality of soils, ground, and surface waters is specifically vulnerable in climatic regions where agricultural production occurs mostly by irrigation such as in California. Robust guidelines for managing microirrigation systems are needed so that the principles of sustainable agriculture are satisfied. The main objective of this research was to use an adapted version of the HYDRUS-2D computer model to develop irrigation and fertigation management tools that maximize production, yet minimize adverse environmental effects. This software package can simulate the transient two-dimensional or axi-symmetrical three-dimensional movement of water and nutrients in soils. In addition, the model allows for specification of root water and nitrate uptake, affecting the spatial distribution of water and nitrate availability between irrigation cycles. Recently, we analyzed four different microirrigation systems in combination with five different fertigation strategies for various soil types using a nitrate-only fertilizer, clearly demonstrating the effect of fertigation strategy on the nitrate distribution in the soil profile and on nitrate leaching. In the present study, the HYDRUS-2D model was used to model the distribution of soil nitrogen and nitrate leaching using a urea–ammonium–nitrate fertilizer, commonly used for fertigation under drip irrigation. In addition, the distribution of phosphorus and potassium was modeled. Model simulations are presented for surface drip and subsurface drip tape, each associated with a typical crop in California.
In soil respiration studies the diffusive gas fluxes are often calculated using Fick's law. However, results obtained with Fick's law deviate from those obtained with the theoretically sound Stefan-Maxwell equations. In the present study a numerical model based on an adapted form of Fick's law is applied to soil respiration. A pressure adjustment flux to maintain isobaric equilibrium in the system is employed to correct errors related to the usage of Fick's law. The results of the above-mentioned model are compared with those of analytical solutions of Fick's law and the Stefan-Maxwell equations to check the model's accuracy. The analytical solutions are derived for steady state transport at constant respiration rates in a hypothetical ternary system with N2, O2, and CO2. Calculations are performed at various constant rates of CO2 production and O2 consumption throughout the soil. Differences between the mole fraction gradients calculated with Fick's law and the Stefan-Maxwell equations are substantial. If Fick's law is combined with the isobaric equilibrium correction procedure, the similarity with the Stefan-Maxwell equations is much better. The numerical model employing the adapted Fick's law is subsequently tested against field measurements. Field measurements were carried out in large outdoor lysimeters filled with oil-contaminated soil containing nonvolatile hydrocarbons. Nonsteady gas transport due to dynamic soil respiration during biodegradation of the hydrocarbons in the lysimeters is modeled at known boundary conditions. The result of the model agree with measurements of CO2 fluxes and O2 and CO2 concentration profiles in the lysimeters.
Dissolved O2 concentration ([O2]) in nutrient solution was controlled at 0.01, 0.10 and 0.20 mM with accuracy of +/- 0.005 mM in a newly developed hydroponic system, and the effects of [O2] on water uptake and growth of cucumber plants (Cucumis sativus L.) were analyzed. For evaluating water uptake rate under the control of [O2], water flux at the stem base was measured on-line with +/-5% in accuracy, 1 mg s-1 in resolution and 1 min in time constant by heat flux control (HFC) method. Water uptake rate was drastically increased by lighting to the plant at each [O2], and water uptake per day was depressed in proportion to decrease in [O2]. In the plants grown for 10 days, leaf area, fresh weight and dry weight of leaves decreased at lower [O2], while stem length and number of leaves were scarcely affected. These facts suggest that membrane permeability of root cells reduces at lower [O2] through respiration-dependent processes, and growth is inhibited through leaf turgor loss caused by the depressed water uptake of roots in O2-deficient nutrient solution in hydroponics.
Because low concentration of nitrite could be toxic to biological systems and high amounts of nitrite have been observed in a river of northern China since 1990, nitrite from agricultural soil sources should be investigated. In this paper, effects of levels of ammonium-N (NH4+-N), soil pH and nitrification inhibitors on NO2- accumulation, and duration of nitrite in soils were studied. Application of 11.2 mg of nitrapyrin kg(-1) soil or 11.2 mg of sodium azide kg(-1) soil dramatically suppressed nitrite occurrence. Within all incubation times and at all levels of ammonium-N input, we did not detect any measurable NO2-N accumulation in samples of Yellow-brown earth (pH 5.67), but observed huge accumulation in the 2 alkaline soils, Fluvo-aquic loam (pH 7.89) and Fluvo-aquic sand (pH 8.20). The concentrations of nitrite in both alkaline soils were related to ammonium-N levels. The effect of pH on nitrite accumulation was demonstrated by using slurries of Fluvo-aquic sand under continuous aeration and buffers of different pH. Data showed that nitrite concentration increased with the elevated pH, yet that ammonia oxidizers from the original soil (pH 8.2) could adapt to the new medium of low pH (pH 5.35). Dynamic changes of nitrite in soils amended with different rates of nitrite-N were also measured in 6 days. Thereby, we concluded that nitrite was unstable in acid soils, but durable in alkaline soils. The authors suggested that NO2- accumulation in field soils and its subsequent environmental impact should receive more attention.
Examination of Treatments for the Prevention and Amendment of Damage Caused by TWW Irrigation in Orchards Planted on Clay Soils. Final Project Report, Project No. 21-16-004. The Office of the Chief Scientist
- J Tarchitzky
- A Bar-Tal
- M Shenker
- G Levi
- A Eshel
- S Cohen
- D Roso
- A Furman
- A Schwartz
- H Cohen
- M Peres
Tarchitzky, J., Bar-Tal, A., Shenker, M., Levi, G., Eshel, A., Cohen, S., Roso, D.,
Furman, A., Schwartz, A., Cohen, H., Peres, M., 2018. Examination of Treatments
for the Prevention and Amendment of Damage Caused by TWW Irrigation in
Orchards Planted on Clay Soils. Final Project Report, Project No. 21-16-004. The
Office of the Chief Scientist, Ministry of Agriculture and Rural Development,
Israel (in Hebrew).
Wastewater: the Untapped Resource. The United Nations World Water Development Report
United Nations World Water Assessment Programme (WWAP), 2017. Wastewater:
the Untapped Resource. The United Nations World Water Development Report
2017. UNESCO, Paris.
Water uptake and growth of cucumber plants (Cucumis sativus L.) under control of dissolved O2 concentration in hydroponics
- Yoshida