Article

Irrigation with treated wastewater containing nanobubbles to aerate soils and reduce nitrous oxide emissions

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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.

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... 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. ...
Article
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.
... 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. ...
Article
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.
... 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). ...
Article
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. ...
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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] . ...
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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.
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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.
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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.
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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.
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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.
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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 (W<sub>1</sub>N<sub>1</sub>) was 90% of the treatment of micro-nano bubble aerated irrigation and 180 kg N/ha fertilizer used (W<sub>1</sub>N<sub>2</sub>), 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.
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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 O2 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 O2 diffusion from the atmosphere to the root zone and by the diffusive resistance of the mucilage layer. Several O2 –diffusive flow models are proposed and discussed with regard to the different geometries, relevant length scales, boundary conditions, and sinks. Soil aeration by advective O2 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 O2 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 O2 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 O2 consumption (and CO2 production) two- to threefold. The ratio between emitted CO2 and inspired O2 (respiratory quotient) is not unity (on a molar basis) but rather depends on the types of respiring populations and environmental conditions. Reduced O2 and elevated CO2 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 O2 concentration, air content, and O2 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 O2 bubbles or H2 O2 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.
Chapter
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.
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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.
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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.
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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.
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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.
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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.
Article
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.
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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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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.
Article
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