Canadian Journal of Soil Science

In the digital age, soil data has become crucial for understanding the role of soil in agricultural systems, biodiversity, carbon sequestration, ecosystem services, and sustainability, thus guiding decision-making. However, diverse data collection methods and fragmented soil data management practices complicate creation of a unified soil database from varied datasets. In Ontario, Canada, data fragmentation across different institutions hinders access and use of this vital soil data for spatial and temporal analyses. Moreover, the latest update in the National Pedon Database is dated back to 2011, underscoring the need for centralized provincial data warehouses for systematic soil information access and analysis. This study addressed these challenges by developing and implementing an end-to-end, multidimensional soil data curation framework that integrates diverse soil data genres and sources in Ontario, enhancing the database updating process. Applying minimum inclusion criteria, data from thirteen sources across four different data genres (fixed depth, peatland, profile, and topsoil), comprising 14,145 observation sites and their respective layers, were integrated into an SQLite database. Despite dense sampling in southern Ontario, data gaps increased with depth. Harmonization focused on key attributes such as depth, soil organic carbon, and texture yielded 6,335 unique sites and 28,134 layers, including 5,460 profiles, 178 topsoil, and 697 fixed depth sites. Using a scalable and transparent soil data ‘hyperlooping’ framework, integrated with platforms like KNIME, R, and SQL, this comprehensive database supports enhanced digital soil assessment and mapping in Ontario, and beyond.

La production du maïs à ensilage dans la région du Saguenay–Lac-Saint-Jean (SLSJ) est limitée en raison du faible nombre d’unités thermiques maïs (UTM). Pour pallier cette contrainte, plusieurs producteurs utilisent un film de plastique translucide dit « oxo-biodégradable », permettant ainsi de devancer la date de semis et de bénéficier d’hybrides plus élevés en UTM. Toutefois, l’utilisation de ce type de plastique pourrait causer des problèmes importants en s’accumulant notamment dans les sols, les sédiments, les eaux et les organismes vivants. À ce jour, il demeure toutefois difficile de connaître les superficies recouvertes par ce plastique au fil des années. Nous avons entrepris une première étude pour connaître l’étendue de l’utilisation de cette pratique depuis 2018 dans la région à l’aide d’images satellitaires. Nos résultats indiquent que les superficies consacrées à cette pratique ont bondi de 90% au cours des sept (7) dernières années, passant de 1 192 ha en 2018 à plus de 2 300 ha en 2024. Nous avons également constaté que l’utilisation de ce paillis de plastique se concentrait sur certains secteurs, dont 44% sur des superficies ayant connu des utilisations annuelles répétées. Annuellement, c’est entre 1.3 et 2.5% de terres agricoles utilisées en grandes cultures qui sont maintenant couvertes par ce paillis de plastique dans la région. La littérature de même que nos observations sur le terrain indiquent également que ce plastique ne se décompose pas au rythme souhaité. Devant ce constat, des études devront être rapidement entreprises afin de trouver des solutions plus durables.

Given potato farm cropping history, the recent introduction of C4 cover crops may provide an in situ opportunity to track their residues by δ13C techniques. From 2019 to 2022 soil (0-15cm) samples were collected on PEI potato farms from 15 paired strips of sorghum sudangrass (SS) and C3 crops. Under C3 crops, soil δ13C was remarkably uniform at -27.7‰ +/- 0.26‰, while SS cover cropping (above ground biomass -12.8‰) significantly enriched soil δ13C values to -27.4‰ +/- 0.38‰. This study demonstrates proof of concept that δ13C techniques can quantify the dynamics of C4 cover crop residues in potato farm soils.

Soil disturbance, reduced crop diversity, and decreased residue in intensively managed systems can negatively impact soil biological communities and soil health. This study examined the impact of long-term (>20 years) low- (forest, grassland), medium- (diversified annual cropping), and high-intensity (annual cropping, frequently to potatoes) land-use on soil nematode communities and soil health in 59 sites across Prince Edward Island, Canada. Soil samples (0–15 cm) were collected at five locations per site and analysed for soil biological (nematode communities, respiration, soil organic matter, permanganate oxidizable carbon (POXc), soil protein), chemical (pH, N, soil N supply, extractable nutrients), and physical (bulk density, texture) properties. Soil pH and extractable nutrients were lowest in the low-intensity sites, while total C and C:N ratios were highest and decreased with increasing land-use intensity (low > medium > high). Soil respiration, POXc, and protein were lowest for high-intensity sites. Low-intensity sites had greater nematode Shannon diversity and richness, and higher maturity and structure indices than the medium- and high-intensity sites (p < 0.05), signifying a more structured nematode community. Nematode communities from the high-intensity sites were more degraded and had significantly higher basal indices compared to the low- and medium-intensity sites. At the trophic level, the low-intensity system had higher numbers of omnivores and lower abundance of bacterivores. These differences in nematode trophic composition may result in differences in ecosystem function, including nutrient cycling and biological control.

Conservation tillage and crop rotation diversification have been promoted to increase soil C and N storage; however, the interactive effects of tillage and crop rotation on soil C and N dynamics remain contradictory. Using a long-term (24-yr) experiment established at a clay loam site (Orthic Humic Gleysol) at Ridgetown, Ontario, Canada, the interactive effects of five crop rotations and two tillage systems were tested on soil organic C (SOC) and total N storage in soil depth increments and in the full soil profile (0-0.6 m) in 2019. While crop rotation influenced SOC and total N concentration in top 0.2 m, these effects were minimized when storage was expressed on an equivalent soil mass basis. Over the 0-0.6 m depth, no-tillage had 24 Mg SOC ha-1 and 4.7 Mg total N ha-1 greater content, respectively, than conventional tillage, supporting the value of no-tillage on increasing soil C and N in the long-term. Interestingly, no interactive effects of crop rotation and tillage on soil C and N storage in 0-0.6 m were observed. While the type of crop species and amount of C and N inputs under different crop rotations are important variables impacting the soil C and N storage, our results suggest that the crop rotation diversity was not a major driver of soil C and N in this study. Future mechanistic investigations exploring the persistence and linkage of soil C and N with crop rotation diversity in the tested production systems are needed.

Improving the concentrations and bioavailability of micronutrients, especially iron (Fe) and zinc (Zn), in crop grains is important to alleviate their deficiencies in humans. Inoculating crops with arbuscular mycorrhizal fungi (AMF) can potentially enhance soil nutrient supply and crop yield, but the effectiveness is influenced by soil factors, particularly soil phosphorus (P) availability. A greenhouse pot experiment was conducted to evaluate the effect of a commercial AMF product on spring wheat (Triticum aestivum L.) yield and grain concentrations of Zn and Fe under different soil P addition levels (0, 5 and 20 mg P kg-1 dry soil). Results showed that AMF inoculation significantly increased root colonization rate of wheat across all P addition levels. Wheat growth, as evidenced by dry weights of shoot and grain, was significantly enhanced by AMF and high P addition treatments. AMF inoculation did not affect grain Zn concentration, but significantly increased grain Fe concentration compared to the un-inoculated control. As expected, P addition resulted in a significant reduction in grain concentrations of Fe and Zn, primarily due to a growth dilution effect. An integrated analysis using the radar plot concludes that AMF inoculation is most effective in increasing crop yield and grain micronutrient concentrations when soil P levels are low. Importantly, while adequate P supply is crucial for maintaining crop productivity, it may decrease grain micronutrient availability without complementary strategies.

We conducted incubation experiments with a paddy soil collected from a long-term field experiment to explore the effect of Chinese milk vetch (Astragalus sinicus L., CMV) application on potential nitrogen (N) denitrification (PDA), nitrification (PNA), mineralization (PNM), soil chemical properties, microbial communities, enzyme activities, yields and nutrient uptake of rice under different fertilization treatments. Five treatments were included: no chemical fertilizers (C0), chemical fertilizers (C100), Chinese milk vetch (M), CMV combined with 100% chemical fertilizers (MC100) and with 80% chemical fertilizers (MC80). Results showed that the M, MC100, and MC80 treatments significantly increased PNM and PNA compared with the C100 treatment (P < 0.05). Meanwhile, the CMV application significantly increased total N, microbial biomass N, and carbon (C) concentrations, the abundances of the bacterial phylum Actinobacteria, and the genera Bradyrhizobium, Mycobacterium, Streptomyces and Reyranella, N-acetyl-glucosaminidase (NAG) activity, yields and N nutrient uptake of rice grain compared with the C100 treatment (P < 0.05). Correlation analyses indicated that grain yield and N uptake of rice, soil total N, microbial biomass C and N, the bacterial phylum Actinobacteria, the genera Bradyrhizobium, Mycobacterium, Streptomyces, Reyranella, and NAG were significantly correlated with PNM under different fertilization regimes, while microbial biomass C and N, Actinobacteria, Bradyrhizobium, and Reyranella were positively related to PNA (P < 0.05). Together, the application of CMV alone or in combination with chemical fertilizers can improve soil properties and rice growth, which may accelerate N mineralization and nitrification in this soil.

Saline–alkali soil is common in north China, especially in the Datong district in north Shanxi province. Improving the soil will benefit the environment and society. Graphene oxide (GO) has been shown to benefit agricultural and forest soils. Herein, we explore three different experimental conditions of CK (CK means irrigated with tap water), CJ (CJ means 0.2 g of bacteria addition and irrigated with tap water), and CJ25 (CJ25 means 0.2 g of composited bacteria plus 25.0 mg/L of GO added and irrigated with tap water) for saline–alkali soil by the addition of optimized amounts of GO and external bacteria. Our results show that the addition of 25.0 mg/L GO and microbial agents increases the number of bacteria and fungi in the soil and improves the species abundance of bacteria and fungi in the saline–alkali soil, while having little effect on species richness. The GO and bacterial treatment increased the abundance of Proteobacteria, Actinobacteriota, Chloroflexi, Pseudomonas, Ascomycota, Mortierella, and Fusarium. These bacteria have been shown to produce proteolytic enzymes and cellulases that decompose lignin and cellulose in litter, and thus play important roles in carbon and nutrient cycling. The addition of GO and microorganisms provides a viable way to improve saline–alkali soils.

Soil compaction, a result of mechanical resistance to penetration, has a direct impact on yield potential by limiting root access to water and nutrients. Factors such as inadequate crop rotation, intensive mechanization and trampling by animals contribute to compaction. Mitigation strategies include crop rotation, control of machinery traffic, the use of cover crops and the use of mechanical techniques. Geostatistical methods in pedostatistics evaluate the spatial variability of soil properties. The aim of this study was to determine the penetration resistance in five soil layers (10cm, 20cm, 30cm, 40 cm, 50cm), identify critical compaction regions and quantify the economic impact of compaction management in a 230-hectare farm in Alegrete, Brazil. A digital penetrometer was used to measure resistance and semivariograms were calculated using classical and robust estimators for interpolation. The evaluation of the economic impact took into account the variable cost differences between the total area and the area required for compaction. The analysis showed a gradual increase in compaction from the surface to the subsoil, with a highly compacted zone occurring at 20-30 cm, signaling the need for monitoring and intervention. The dependency analysis showed a well-defined structure. The results show that geostatistical tools can be used in the assessment of soil penetration resistance, especially in layers from 10 to 20 cm. An efficient identification and quantification of compacted zones within the cultivation area was achieved. This approach proves to be economically viable, especially in extensive farming, suggesting a wide application in agricultural compaction management.

The factors influencing the spatial distribution of fungal communities are commonly examined over large spatial scales but not at smaller scales. Given this, the extent to which soil properties and topographic features contribute to the diversity and distribution of fungal communities in an agricultural field needs to be further explored. We investigated the spatial distribution of soil fungal community composition from a ~1100 m long transect with 83 sampling points in a commercial potato field with a rolling landform. The relative abundance of Ascomycota, Basidiomycota and Mortierellomycota showed medium to strong spatial dependence with an autocorrelation range varying from ~43 to 92 m, similar to the autocorrelation range of soil properties and topographic features. Most of the variability in fungal and saprotrophic community composition was explained by soil properties (15% and 11%, respectively) and spatial distance (16% and 15% respectively). While topographic features contributed 8% and 5% of variability to total fungi and saprotrophic community composition, respectively. The fungal and saprotrophic community compositions were correlated with SOC, pH and slope curvature, however, richness and Pielou’s evenness of the fungal communities and fungal biomass were not correlated with soil properties or topographic features. The results suggest that the spatial variation in fungal and saprotrophic community composition in response to soil properties and topographic features in this agricultural landscape was due to differences in assemblages of fungal Amplicon Sequence Variants (ASVs) but not in differences in the number of fungal ASVs or fungal biomass measured using phospholipids fatty acids.

Geophysical methods like ground-penetrating radar (GPR) and electromagnetic induction (EMI) offer non-destructive, high-resolution alternatives for soil sampling. This study aims to understand subsurface stratifications in boreal podzolic soil employing an integrated GPR–EMI technique and soil sampling. The GPR and EMI confirmed each technique's findings. They provided insights into the spatial variability of electrical conductivity, textural changes, and stratification (detected mainly by GPR reflections) in the soil profile. The assessed soil properties revealed the existence of two contrasting layers within 0–0.60 m depth. The study highlights the potential of using integrated GPR–EMI to identify subsurface stratification in boreal podzolic soil.

There is increasing interest in soil organic carbon (SOC) sequestration as a climate change mitigation strategy. There is a need to estimate the quantity of SOC sequestered historically due to no-till, and the remaining sequestration potential in Saskatchewan. To answer this question, predictive soil mapping results were linked with the Century model to predict SOC stock change over time to a depth of 20 cm considering three different future climate change scenarios. Climate scenarios included low, moderate, and high amounts of climate change and included estimated changes to monthly minimum, average, and maximum temperature, total monthly precipitation, and average monthly relative humidity at an 800 m × 800 m resolution. Historically, the modelled average SOC gain for Saskatchewan was 2.8 Mg ha⁻¹. Future potential simulated SOC was lower over the next 30 years, with average SOC gains estimated to range from 1.4 to 1.7 Mg ha⁻¹ by 2054 and 2.3 to 3.1 Mg ha⁻¹ by 2100. There is also unequal spatial distribution of SOC stock gain potential, with the northern grain growing regions showing lower future potential. The predicted future gains will be at a lower rate than in the past with carbon sequestration rates dropping from 0.06 to less than 0.02 Mg ha⁻¹ year⁻¹. Additional management practices such as improved residue management and the introduction of crop varieties with increased below ground carbon inputs and more stable residues should be explored to offset the diminishing SOC returns from no-till.

Monitoring data are needed to assess the effectiveness of soil conservation measures applied on agricultural lands during pipeline construction. Soil data were collected on the footprint of a pipeline constructed in 2016–2017 in west-central Alberta. Construction practices were expected to mitigate for topsoil loss and admixture, compaction, and erosion. Sites were established on the footprint and on adjacent reference areas on 24 parcels. Field measurements included point-sample results for horizon thickness, bulk density and soil erosion-rate including suspended sediment in runoff, and laboratory measurements from composite samples including pH, total organic carbon and texture. Admixture rate was estimated from change in percentage clay. Topsoil thickness was more variable on the reclaimed footprint than references. Topsoil pH was about 0.4 units higher and percent clay was 6.2% higher on the footprint than references but total organic carbon was not different. Admixture rates in the topsoil at six parcels ranged from 0.18 to 0.60. Penetration resistance on four measured aggregate size classes of subsoil was significantly higher on the footprint than reference. Subsoil loss from rill erosion ranged from 0.1 to 8.1 cm in the first year after construction when little vegetation was present and sediment concentrations in runoff sometimes exceeded 10 g L⁻¹. Mitigations applied to limit soil degradation were less effective than expected. The use of quantitative techniques to monitor soil reclamation outcomes will improve the credibility of results but add costs to the process. Similar monitoring is needed to determine the effectiveness of current reclamation practices.

The H3A-4 extraction is a new method to determine plant available nutrients but has not been compared with standard soil tests or calibrated to crop response in Manitoba, Canada. Olsen P and ammonium acetate K were related to H3A-4 P and K for 961 soil samples. Significant relations were found between Olsen P and H3A-4 (R² = 0.74, P < 0.01) and ammonium acetate K and H3A-4 (R² = 0.83, P < 0.01). New thresholds were established for fertilizer recommendations with H3A-4 as 24 mg kg–1 for P and 32 mg kg–1 for K.

Arbuscular mycorrhizal fungi (AMF) play important roles in the dynamics of soil organic carbon (SOC), as they can promote its accumulation and the formation of soil aggregates, thereby increasing soil carbon storage. However, the impact of carbon input through AMF inoculation on SOC sequestration is still unclear. In this study, the effects of AMF on photosynthetic carbon transport and SOC accumulation in two types of black soils with either high or low SOC soils were analyzed by an outdoor pot experiment using isotope ¹³C labeling, thus, revealing the mechanism of action of AMF in stabilizing SOC fixation. The results showed that AMF symbiosis increased the allocation of photosynthetic carbon to the roots of the maize plant and soils. Inoculation with AMF also increased the proportions of soil macro-aggregates and the soil microbial biomass carbon content in low SOC soil, promoted the accumulation of soil aggregates, and enhanced the chemical composition of SOC. After returning the harvested labeled straw to the original pots the following year after planting, inoculation with AMF was found to increase the contents of hemicellulose and lignin at the time when maize kernels attained a plump appearance. AMF significantly increased glomalin-related soil protein in high SOC soil. In addition, AMF had a promoting effect on the decomposition of cellulose, hemicellulose, and lignin in the straw, which could subsequently increase the accumulation of carbon. We provide evidence for the promotion of soil aggregates, soil C accumulation, and SOC sequestration with AMF inoculation.

Soil organic carbon (SOC) content is a key metric of soil quality and limited work has been done to examine the effect of long-term conservation agriculture management practices (CAMP) on SOC pools within western Canadian soils. We assessed the nature and permanence of sequestered SOC within 90 diverse Saskatchewan surface (0–10 cm) agricultural soils before and after 21 years of CAMP. Comparisons were made of total SOC, labile and dynamic SOC fractions (light fraction, water-extractable, and microbial biomass), respirable CO2–C during a 6-week incubation, along with spectroscopic characterization using ¹³C/¹²C stable isotope ratio and ATR-FTIR. Among soil climatic zones, the SOC content increased in the semi-arid Brown and Dark Brown soils, ranging from 2.4 to 3.7 Mg C ha⁻¹ (111.4–187.7 kg C ha⁻¹ year⁻¹), but did not change in the subhumid Black, Dark Gray, and Gray soils. Overall, soils having the smallest initial SOC level were most responsive to CAMP and accumulated more SOC. According to the δ¹³C data, CAMP appeared to reduce annual crop moisture stress, especially within the Brown soil zone. Decreased light fraction and water-extractable SOC contents in Black, Dark Gray, and Gray soils could reflect more intense decomposition and greater surface stratification of crop residues. Brown soils experienced the largest increase in microbial biomass-C content. The CO2–C emissions from the Brown, Dark Brown, and Gray soils under CAMP suggest greater SOC stability in 2018 compared with 1996. The ATR-FTIR data pointed to enhanced SOC persistence, via more stabilized SOC forms and mineral-associated organic C fractions.

While cover crops (CC) are known to enhance soil health, outcomes are often subtle and confined to a shallow surface soil layer. We assessed 15 soil health indicators over three CC trials with a 15-species Blend polyculture, a Mustard biculture (white (Sinapsis alba L.) and brown (Brassica juncea (L.) Czern.) mustards), Buckwheat (Fagopyrum esculentum Moench), and Faba bean (Vicia faba L.) monocultures, and a Weedy fallow (no CC, weeds allowed to grow) on an organic farm in southern Alberta. Soil sampling times included (i) summer pretermination; (ii) fall post-termination; and (iii) spring post-termination of CC. Twelve of 15 soil health indicators showed significant effects of CC treatment for at least one sampling time. Soil organic C (SOC) ranked highest with 80% of sampling times showing significant CC effects. N-related indicators (total N (TN), nitrate-N)) were also quite sensitive, being significantly affected by CC treatment at 60% of sampling times. Three soil health indicators (acid phosphomonoesterase (AcP), wet aggregate stability, and free-living nematodes (FLN)) were consistent in their nonresponses to CC treatment at all sampling times. Comparing CC treatments with a Weedy fallow, showed that not all enhancements of soil health were explained by inclusion of a CC, with Weedy fallow as effective for some indicators. A polyculture Blend significantly enhanced soil health over a monoculture CC or Weedy fallow in 46% of instances of soil health indicator improvement. While CC led to enhancement of soil health, results were not always consistent, being contingent on specific indicators.

In Canada, there is a need to implement value-added uses for wood ash (hereafter ash) generated from bioenergy facilities as most ash is landfilled. Ash application to forests can provide benefit via nutrient supply, amelioration of soil acidity and, sometimes, increased tree growth. However, information is limited on the response of conifer species to different wood ash types applied to fine-textured soil typical of north-central B.C. We conducted a 16-month seedling pot trial that examined the response of Douglas-fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta var. latifolia), and hybrid white spruce (Picea glauca × engelmannii) to high- (HCA) and low-carbon ashes (LCA) applied (up to 10 Mg mineral matter ha⁻¹ equiv.), with and without fertilizer N (200 kg N ha⁻¹ equiv.), to fine-textured forest soil. Pine and spruce exhibited a 1.6- and 1.4-fold increase in shoot biomass at the high rate of HCA with fertilizer N. At study end, the high rate of LCA had the greatest soil pH, EC and total K in the upper forest floor, but the HCA had greater total B, P and Zn. LCA elicited increased foliar B in pine, but HCA increased foliar Ca in spruce when co-applied with fertilizer N. In general, Douglas-fir growth did not respond to ash treatments, and seedling mortality was observed in some LCA treatments. Ash treatments helped offset some nutrient deficiencies induced by N fertilization. Ash type influenced soil chemical as well as seedling growth and nutrition responses.

I offer this perspective as hope that miyo wîcêhtowin (translated as “good relations” in Plains Cree) can be established between the discipline of soil science and Indigenous Peoples in Canada. This perspective reflects not only on the difficult truths of why the relationship between Indigenous Peoples and soil science is primarily one of exploitation and neglect, but also on how fostering a relationship built on reciprocity presents opportunities for Indigenous knowledge systems and soil science to improve the way we relate to land and how we steward soil. Soil science was borne in this country as an instrument of colonization of the plains, marginalizing First Nations from their lands and livelihoods through agricultural settlement. It is necessary to illuminate this fraught history to understand the contemporary realities of First Nations in the prairies, including the hopeful efforts First Nations are making towards conservation and restoration of prairie landscapes—and revitalization of Indigenous knowledge systems—especially though buffalo rematriation. This sharing is done in the hope that we can collectively work towards reciprocity in the relationship between Indigenous Peoples and soil science as a discipline for improved caretaking of the land.

No-till (NT) often causes prominent stratification of C and nutrients in the soil profile relative to tilled systems. We hypothesize differences in root distribution within the soil profile between NT and tilled systems could be one factor contributing to stratification. We evaluated how NT affects root length density (RLD), root biomass yield (RBY), and root diameter compared with other tillage systems and factors that may affect root characteristics. We reviewed studies until 23 January 2024 where RLD, RBY, or root diameter were reported under NT and tillage. The data on RLD, RBY, and root diameter were tabulated and the weighted log response ratio (MLRR) and confidence intervals computed. Our meta-analysis showed NT increased RLD in the 0–10 cm depth, but it reduced RLD at 10–20 cm. It increased RBY and root diameter in the 0–20 cm depth and reduced both characteristics at 20–30 cm. Regardless of root characteristics, NT had mixed effects below 30 cm. However, across the soil profile (minimum 50 cm depth), NT had no effect on RLD and RBY. NT-induced changes in roots can be related to increased compaction at the tillage interface. NT stratified both RLD and RBY compared with high-intensity tillage systems, although there were some conditions where NT stratified only RLD or RBY. NT did not induce stratification of RLD and RBY in dry regions, mild, or hot climates, in medium-textured soils, or compared with intermediate-intensity tillage systems. Overall, NT can result in stratification of both RBY and RLD compared with high-intensity tillage systems.

Intercropping or agroforestry systems are among the strategies used to prevent soil erosion or crusting and water loss by evaporation in the bare soil during early growth stage of tree crop plantations. However, the pattern of water use in intercropped, juveline orchard crop plantations is still poorly known. This study aimed to evaluate competition or facilitation for soil water stored by cover crops in rotation and the impact of additional fertilization in a juvenile tung-based intercropping system in southern Brazil during the winter and summer periods of 2012/2013 and 2013/2014 growing seasons. A split plot in randomized complete block design arrangement, with four replications, was used comprising crambe winter cover crop plus poultry manure or nitrogen, potassium and phosphorus (NPK) fertilizer; a mixture of oats and vetch, sunflower, and soybean in rotation; and sole tung as control. Cover crop intercropping significantly increased water content of the surface layer of the juvenile tung soil only at the beginning of the second growing season. The cover crops showed interspecific facilitation for water use by tung during the summer period, but no clear-cut trend for the winter cover crops. The additional organic manure did not enhance profile soil water storage. Any of the summer cover crops (soybean, sunflower, or peanut) could be used for soil and water conservation in juvenile tree crop plantations. Further studies are required during the winter season to establish whether the winter cover crops are competitors or facilitators for stored soil water in agroforestry systems.

Pavement design methods based on principles of unsaturated soil mechanics take into account high soil shear strength due to matric suction resulting in more economical design especially in long roads. In this study, the bearing capacity of two-layer unsaturated sand was investigated using both analytical and experimental methods. At first, using the limit equilibrium method an analytical formula was proposed to determine the bearing capacity of two-layer unsaturated sand in which linear suction profile was considered in soil layers. It should be considered that the constant matric suction distribution assumed by the previous researchers does not show the real profile of matric suction within the soil, sometimes resulting in miscalculated unsaturated bearing capacity. Also, the bearing capacity of two-layer unsaturated poorly graded sand was investigated experimentally in different suctions by a special unsaturated chamber apparatus (UCA) designed for this purpose. The results show more than double increase of unsaturated soil bearing capacity with Sr = 25% compared to saturated soil. The formation of failure wedges in all experiments was investigated by image processing. An acceptable agreement was obtained between the theoretical and experimental bearing capacity results.

Conservation agriculture (CA) is increasingly promoted to build soil organic matter (SOM) based on findings from predominantly small-plot long-term agroecosystem experiments (LTAEs), with minimal on-farm data. Using commercial producer fields (n = 20) in the Brown Chernozemic soil zones of Saskatchewan, Canada, which were sampled before (1996) and after (2018) adopting direct-seeding and continuous cropping (1997), we examined changes in soil organic carbon (SOC) and soil total nitrogen (STN) stocks, along with C and N stocks in particulate (POM) and mineral-associated organic matter (MAOM), and compared them to an LTAE in the same soil zone. After 21 years, SOC and STN stocks (0–30 cm depth) increased by 13% and 21%, respectively, in commercial producer fields, and were more pronounced in finer- than coarser-textured soils. Conversely, there were no significant changes (0–30 cm depth) after 18 years (1998–2016) with CA (continuous wheat and pulse-wheat under no-tillage (PW-NT)) in the LTAE, except that STN stock for PW-NT decreased by 7.7%. The estimated rate of change to 30 cm depth was similar between the commercial fields and LTAE for SOC (0.28 and 0.16 Mg C ha⁻¹ year⁻¹, respectively), but not STN (0.04 and −0.03 Mg N ha⁻¹ year⁻¹, respectively). Changes were more evident in the MAOM than POM fraction in both cases. Although the impact of CA may be similar, as observed for SOC, actual on-farm changes will depend on site-specific factors, and specific CA practice. Therefore, on-farm monitoring studies are needed for more accurate assessments of SOM changes and C sequestration potentials.

Prairie cordgrass (PCG) is a perennial crop which has the potential for biofuel production under marginal lands. The intercropping of a perennial legume, kura clover (KC) with PCG can reduce the use of chemical fertilizer while maintaining the soil hydro-physical conditions. The objective of this study was to compare the soil hydro-physical properties and greenhouse gas (GHG) fluxes under PCG intercropped with KC (PCG–KC), and PCG fertilized with graded levels of N (0, 75, 150, and 225 N kg ha⁻¹). During the summer of 2021, soil samples (0–10 cm) were collected. Additionally, gas samples were collected weekly from April through September of the same year. Soil water retention, saturated hydraulic conductivity (Ksat), thermal conductivity (λ), soil organic carbon (SOC), and total N (TN) concentrations were measured. Soil pore characteristics were measured using X-ray computed tomography. The PCG–KC had 1.42 g kg⁻¹ TN and 24 g kg⁻¹ SOC at 0–10 cm, non-significant to PCG-75, 150, and 225 N. Nonetheless, TN significantly increased in both PCG–KC and other fertilized treatments compared to the control. Intercropping boosted macroporosity (0.024 cm³ cm⁻³), Ksat (+50%), and lowered λ (−1%), compared to the N fertilized treatments. Soil cumulative CO2 under PCG–KC (1012.67 kg C ha⁻¹) was similar to PCG-75, 150 N, but lower than PCG-225 N (1418.66 kg C ha⁻¹). Overall, this study showed that PCG–KC can be a sustainable option over the use of N fertilizers since they had similar levels of hydro-physical characteristics and had a comparable ability to mitigate GHG emissions.

Rice is sensitive to salt stress, commonly caused by high concentrations of sodium (Na) in soils. However, the concentration and spatial variability of exchangeable Na in lowland paddy fields of Sri Lanka are not known. This study examined the interactive effects of the agro-climatic zones (ACZs), soil orders, and water sources on exchangeable Na in lowland paddy fields in Sri Lanka using 8566 soil samples. Exchangeable Na was extracted using 0.01 mol/L CaCl2 solution and detected using inductively coupled plasma-mass spectrophotometry. Exchangeable-Na concentration ranged from 0.05 to 4814 mg kg⁻¹ with a mean concentration of 140.7 mg kg⁻¹, and these values were within the optimal range reported for tropical paddy soils. The distribution of exchangeable Na was right skewed with 44%, 35%, and 9.3% of samples falling into 0–100, 100–200, and 200–300 mg kg⁻¹, respectively. Samples from the Low country Dry zone had the highest (157 mg kg⁻¹) Na concentration while that in the Upcountry Intermediate zone was the lowest (13 mg kg⁻¹) (p < 0.05). Vertisols recorded the highest (255 mg kg⁻¹) and Ultisols recorded the lowest (81 ± 5.0 mg kg⁻¹) among soil orders. Soils receiving supplementary irrigation in Low country Dry zone had lower Na than that in rainfed systems. Exchangeable-Na concentration was positively correlated with soil pH (p < 0.05). Even though the concentrations of Na in soil samples were within the optimal range, agronomic decisions based on ACZ, soil order, and water source need to be made to minimize the potential development of saline–sodic soils in the study areas.