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Background and Aims: Storing carbon (C) within soils is significant for maintaining soil-health and reinforces the feedback loop of C loss from soils as CO2 to the atmosphere. Seasonal variation with increased temperatures and inconsistent precipitation as climate change consequences also affect the soil C-sequestration process globally. Soil-health management practices (SHMPs) such as cover crops, crop residues and manures increase organic components as well as soil-organic C (SOC) pool in an agroecosystem. While, soil microbial-biomass (SMB) which is considered as a soil-health metric to understand microbial community response, is still not modelled to relate with SOC and seasonal impacts to identify suitable SHMPs. Methods: Cover crops followed by 100% residue addition and combinations of manure +organic-fertilizer were the SHMPs for a winter-wheat system in our field study. Seasonal data regarding SOC, nitrogen, SMB-C and labile-C content of soils were used to machine-learn the system and understand the influence of different drivers on SMB-C. Results: The test models based on ‘Multivariate Linear Regression’ could explain 70% of the variability and predicted seasonal-variation as a dominant variant followed by SHMPs and soil-moisture. AdaBoost and Random Forest Models performed better than others if ‘Ensemble Learning’ was used. ‘Feature Importance’ predicted labile-C and aboveground-biomass as the two most important drivers impacting SMB-C. Conclusions: Ensemble Learning’ method of Machine-Learning could be successfully implied to understand the SMB-C in an agroecosystem and set benchmark-strategies for soil-health improvement. 50% manure+ 50% fertilizer with crop-residue could be recommended for maximum labile-C and SOC in surface soil-layers.

Soil organic and inorganic carbon (SOC & SIC) and microbial community structure are key indicators of soil quality and productivity in arid-saline soils. Salinity stress and diminishing availability of freshwater (FW) for irrigation are major constraints for productivity and improving soil quality indicators. Using treated wastewater (TW) and implementing climate-smart cropping systems are promising alternatives to replace freshwater usage in intensive cropping systems, however, impacts on the microbial community and net-carbon sequestration potential are not clearly understood. This field study was conducted in an arid saline-soil to investigate soil microbial community structure and soil carbon contents under a combination of treatments comparing bioenergy sorghum (So) and switchgrass (Sg), two irrigation water sources (FW & TW), and gypsum amendment (GA), to a native-soil control. After three years of implementing these treatments, soil samples were collected and analyzed for total carbon (TC), SOC, SIC, microbial biomass-carbon (MBC) and microbial community structure. Results showed that TW increased microbial diversity and shifted the community structure towards copiotroph-dominated prokaryotes. Several predominant and responsive taxa were associated with divergent trends of SOC, SIC and salinity parameters. Both SOC and SIC pools were sensitive to treatments and demonstrated divergent trends, as contents of TC and SOC were higher in TW-treatments, but of SIC were significantly lower in several So_TW treatments. Treatment TW_So_GA assembled a distinctive microbial community structure, accumulated the highest content of SOC (7.66 g kg−1) but recorded the lowest content of SIC (6.63 g kg−1). The lowest content of SOC was observed in native soil (4.58 g kg−1) but contained the highest SIC (8.15 g kg−1). The study results revealed the agronomic systems with higher potential for increasing TC and SOC content in arid-saline soils. Surface soil SIC was responsive to agronomic management, and several treatments produced disparate impacts on SOC and SIC stocks, which warrant for considering TC as the key indicator for assessing carbon sequestration in arid lands.

Soil is a vital component of the ecosystem that drives the holistic homeostasis of the environment. Directly, soil quality and health by means of sufficient levels of soil nutrients are required for sustainable agricultural practices for ideal crop yield. Among these groups of nutrients, soil carbon is a factor which has a dominating effect on greenhouse carbon phenomena and thereby the climate change rate and its influence on the planet. It influences the fertility of soil and other conditions like enriched nutrient cycling and water retention that forms the basis for modern ‘regenerative agriculture’. Implementation of soil sensors would be fundamentally beneficial to characterize the soil parameters in a local as well as global environmental impact standpoint, and electrochemistry as a transduction mode is very apt due to its feasibility and ease of applicability. Organic Matter present in soil (SOM) changes the electroanalytical behavior of moieties present that are carbon-derived. Hence, an electrochemical-based ‘bottom-up’ approach is evaluated in this study to track soil organic carbon (SOC). As part of this setup, soil as a solid-phase electrolyte as in a standard electrochemical cell and electrode probes functionalized with correlated ionic species on top of the metalized electrodes are utilized. The surficial interface is biased using a square pulsed charge, thereby studying the effect of the polar current as a function of the SOC profile. The sensor formulation composite used is such that materials have higher capacity to interact with organic carbon pools in soil. The proposed sensor platform is then compared against the standard combustion method for SOC analysis and its merit is evaluated as a potential in situ, on-demand electrochemical soil analysis platform.

Investigating the impact of cover crops and manure on soil greenhouse gas (GHG) emissions is crucial for advancing our understanding of the climate-smart potential of organic management practices. This soil incubation experiment was conducted to investigate the combined effects of manure and cover crop residue decomposition on soil carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions under simulated tillage conditions. Undisturbed soil cores, collected from an organic cotton (Gossypium hirsutum L.) field experiment, were incubated for 90 days in a 2 × 4 factorial design for 2 consecutive years. Four combinations of cover crop and poultry litter (PL) residues were the primary treatment factor. The amount of residues added in the incubation study reflected the cover crop biomass produced under field conditions and the amount of PL applied in the field. Residue treatments included PL only at the full application rate (250 kg ha−1), PL with oat (Avena sativa L.), PL with turnip (Brassica rapa subsp. rapa), and half the rate of PL with Austrian winter pea (Pisum sativum) (AWP). The residues were either soil incorporated or surface applied to simulate disking and no-till field conditions. On average, 3.5% of applied carbon escaped as CO2 during the 90-day incubation period across treatments. Similarly, on average, 0.75% of applied nitrogen escaped as N2O. The proportion of nitrogen emitted as N2O under simulated no-till was 81.2% higher in 2020 (P < 0.05) compared to conventional tillage. In 2021, N2O emission was 35.8% higher (P < 0.1). When normalized over the amount of carbon added, total CO2 equivalent GHG emissions were the highest in the legume AWP treatment for both years. However, neither residue types nor simulated tillage affected net soil CH4 uptake (P > 0.1). While no-till practices may increase soil total carbon and nitrogen stocks during the cover crops and manure decomposition, the impact on GHG emissions depends on residue type and should be considered in estimating the climate-smart potential of organic management practices. [ABSTRACT FROM AUTHOR]

Application of date palm waste compost is quite beneficial in improving soil properties and crop growth. However, the effect of its application on soil microbial communities is less understood. High-throughput sequencing and quantitative real-time PCR (qPCR) were used to evaluate the effect of compost application on the soil microbial composition in a barley field during the tillering, booting and ripening stages. The results showed that compost treatment had the highest bacterial and fungal abundance, and its application significantly altered the richness (Chao1 index) and α-diversity (Shannon index) of fungal and bacterial communities. The dominant bacterial phyla found in the samples were Proteobacteria and Actinobacteria while the dominant fungal orders were Ascomycota and Mortierellomycota. Interestingly, compost enriched the relative abundance of beneficial microorganisms such as Chaetomium, Actinobacteriota, Talaromyces and Mortierella and reduced those of harmful microorganisms such as Alternaria, Aspergillus and Neocosmospora. Functional prediction based on Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) showed that amplicon sequence variant (ASV) sequences related to energy metabolism, amino acid metabolism and carbohydrate metabolism were associated with compost-treated soil. Based on Fungi Functional Guild (FUNGuild), identified fungi community metabolic functions such as wood saprotroph, pathotroph, symbiotroph and endophyte were associated with compost-treated soil. Overall, compost addition could be considered as a sustainable practice for establishing a healthy soil microbiome and subsequently improving the soil quality and barley crop production.

The valorization of date palm wastes as bioresources has received little attention. In this context, the feasibility of date palm waste valorization through composting and the application effects on barley plants production under control condition was investigated. The principal requirements for compost to be safely used are stability and maturity that refer, respectively, to the microbial biomass activity's level, germination tests, and plant growth bioassays or phytotoxicity. Indeed, the phytotoxicity of composted date palm waste used for seed germination and seedling growth bioassays was researched. The finished compost values of the C/N ratio were 15.36 and 18.58%, 1.21%, 0.54%, and 0.95% for total organic carbon, N, P, and K contents, respectively. The concentration of heavy metals and microelements were lower and met the requirement established by national standards. Moreover, the end product was free from harmful pathogens like Salmonella, Escherichia coli, total coliforms, and fecal coliform bacteria. Application of compost extract (especially 25%, 50%, and 75%) did not affect barley seed germination, stimulated hypocotyl and radicle growth and is characterized by a GI exceeding 90%, demonstrating its stability and lack of phytotoxic effect. Moreover, compost promotes plant growth, improved physiological parameters, photosynthetic pigments, and plant biomass. According to the results, the prepared compost especially at the dose T3 (soil amended with 30 t/ha) increased the nutrients availability and uptake which may be the reason for an increase in photosynthetic activity, chlorophyll synthesis, and dry matter accumulation. Composting may well represent an acceptable solution for disposing of date palm waste and be of great interest to sustainable agriculture in Tunisia oasis ecosystems. [ABSTRACT FROM AUTHOR]

Proteomic analysis was performed to investigate the differentially abundant proteins (DAPs) in barley roots during the tillering stage. Bioinformatic tools were used to interpret the biological function, the pathway analysis and the visualisation of the network amongst the identified proteins. A total of 72 DAPs (33 upregulated and 39 downregulated) among a total of 2580 proteins were identified in response to compost treatment, suggesting multiple pathways of primary and secondary metabolism, such as carbohydrates and energy metabolism, phenylpropanoid pathway, glycolysis pathway, protein synthesis and degradation, redox homeostasis, RNA processing, stress response, cytoskeleton organisation, and phytohormone metabolic pathways. The expression of DAPs was further validated by qRT-PCR. The effects on barley plant development, such as the promotion of root growth and biomass increase, were associated with a change in energy metabolism and protein synthesis. The activation of enzymes involved in redox homeostasis and the regulation of stress response proteins suggest a protective effect of compost, consequently improving barley growth and stress acclimation through the reduction of the environmental impact of productive agriculture. Overall, these results may facilitate a better understanding of the molecular mechanism of compost-promoted plant growth and provide valuable information for the identification of critical genes/proteins in barley as potential targets of compost.

Arsenic (As) bioavailability in the rice rhizosphere is influenced by many microbial interactions, particularly by metal-transforming functional groups at the root-soil interface. This study was conducted to examine As-transforming microbes and As-speciation in the rice rhizosphere compartments, in response to two different water management practices (continuous and intermittently flooded), established on fields with high to low soil-As concentration. Microbial functional gene composition in the rhizosphere and root-plaque compartments were characterized using the GeoChip 4.0 microarray. Arsenic speciation and concentrations were analyzed in the rhizosphere soil, root-plaque, pore water, and grain samples. Results confirmed several As-biotransformation processes in the rice rhizosphere compartments, and distinct assemblage of As-reducing and methylating bacteria was observed between the root-plaque and rhizosphere. Results confirmed higher potential for microbial As-reduction and As-methylation in continuously flooded, long term As-contaminated fields, which accumulated highest concentrations of AsIII and methyl-As concentrations in pore water and rice grains. Water management treatment significantly altered As-speciation in the rhizosphere, and intermittent flooding reduced methyl-As and AsIII concentrations in the pore water, root-plaque and rice grain. Ordination and taxonomic analysis of detected gene-probes indicated that root-plaque and rhizosphere assembled significantly different microbial functional groups demonstrating niche separation. Taxonomic non-redundancy was evident, suggesting that As-reduction, -oxidation and -methylation processes were performed by different microbial functional groups. It was also evident that As transformation was coupled to different biogeochemical cycling processes (nutrient assimilation, carbon metabolism etc.) in the compartments and between treatments, revealing functional non-redundancy of rice-rhizosphere microbiome in response to local biogeochemical conditions and As contamination. This study provided novel insights on As-biotransformation processes and their implications on As-chemistry at the root-soil interface and their responses to water management, which could be applied for mitigating As-bioavailability and accumulation in rice grains.

Core Ideas Impacts of soil moisture at incorporation of two legumes on the CO2 and N2O emissions were studied. Availability of soil moisture led to rapid mineralization of biomass C and N. Legume incorporation based on short‐term rainfall forecast did not avoid large N2O emissions. Carbon dioxide (CO2) and nitrous oxide (N2O) emissions from decomposing legume green manures largely depend on soil moisture. A potential management to mitigate N2O emissions could be to incorporate legumes during dry periods based on the short‐term rainfall forecast. The present mesocosm study was designed to examine the impact of soil moisture due to different timing of rainfall after incorporation of legume cover crops on CO2 and N2O emissions. Two timings of rainfall were simulated as early and late rainfall that received 80 mm deionized water at or 1 wk after incorporation of the legumes. An additional 20 mm water was added after 2 wk of the first simulated rainfalls. Gas fluxes of CO2 and N2O were measured using closed chamber method for 28 d incubation assay. Soil concentrations of NH4+ and NO3–, concentrations of N in undecomposed biomass, and abundances of denitrifier bacterial genes (nirK, nirS, and nosZ) and arbuscular mycorrhiza fungi (AMF) were determined at weekly intervals. Carbon dioxide emissions increased immediately after the first simulated rainfall events and peaked around Day 2 to 3, whereas N2O emissions reached peak level around Day 8 to 10 from both legume treatments. After the first rainfall simulations, soil NH4+ and NO3– concentrations increased, whereas biomass N concentrations decreased rapidly. Abundance of nirK, nosZ, and AMF was positively correlated (P < 0.05) to N2O emissions. Dynamics and magnitude of emissions after first rainfall events remained similar irrespective of the timing of simulated rainfall. In conclusion, our results indicated that soil incorporation of legumes based on a short‐term rainfall forecast may not be an effective tool to avoid large N2O emissions.

Soil enzymes mediate key processes and functions of the soils, such as organic matter decomposition and nutrient cycling in both natural and agricultural ecosystems. Here, we studied the activity of five extracellular soil enzymes involved in the C, N, and P-mineralizing process in both litter and surface soil layer of rainforest in the northwest region of the Colombian Amazon and the response of those soil enzymes to land use change. The experimental study design included six study sites for comparing long-term pasture systems to native forest and regeneration practices after pasture, within the main landscapes of the region, mountain and hill landscapes separately. Results showed considerable enzymatic activity in the litter layer of the forest, highlighting the vital role of this compartment in the nutrient cycling of low fertility soils from tropical regions. With the land use transition to pastures, changes in soil enzymatic activities were driven by the management of pastures, with SOC and N losses and reduced absolute activity of soil enzymes in long-term pastures under continuous grazing (25 years). However, the enzyme activities expressed per unit of SOC did not show changes in C and N-acquiring enzymes, suggesting a higher mineralization potential in pastures. Enzymatic stoichiometry analysis indicated a microbial P limitation that could lead to a high catabolic activity with a potential increase in the use of SOC by microbial communities in the search for P, thus affecting soil C sequestration, soil quality and the provision of soil-related ecosystem services.

Microbial reduction of toxic hexavalent chromium (Cr(VI)) in-situ is a plausible bioremediation strategy in electron-acceptor limited environments. However, higher [Cr(VI)] may impose stress on syntrophic communities and impact community structure and function. The study objectives were to understand the impacts of Cr(VI) concentrations on community structure and on the Cr(VI)-reduction potential of groundwater communities at Hanford, WA. Steady state continuous flow bioreactors were used to grow native communities enriched with lactate (30 mM) and continuously amended with Cr(VI) at 0.0 (No-Cr), 0.1 (Low-Cr) and 3.0 (High-Cr) mg/L. Microbial growth, metabolites, Cr(VI), 16S rRNA gene sequences and GeoChip based functional gene composition were monitored for 15 weeks. Temporal trends and differences in growth, metabolite profiles, and community composition were observed, largely between Low-Cr and High-Cr bioreactors. In both High-Cr and Low-Cr bioreactors, Cr(VI) levels were below detection from week 1 until week 15. With lactate enrichment, native bacterial diversity substantially decreased as Pelosinus spp., and Sporotalea spp., became the dominant groups, but did not significantly differ between Cr concentrations. The Archaea diversity also substantially decreased after lactate enrichment from Methanosaeta (35%), Methanosarcina (17%) and others, to mostly Methanosarcina spp. (95%). Methane production was lower in High-Cr reactors suggesting some inhibition of methanogens. Several key functional genes were distinct in Low-Cr bioreactors compared to High-Cr. Among the Cr resistant microbes, Burkholderia vietnamiensis, Comamonas testosterone and Ralstonia pickettii proliferated in Cr amended bioreactors. In-situ fermentative conditions facilitated Cr(VI) reduction, and as a result 3.0 mg/L Cr(VI) did not impact the overall bacterial community structure.

Abstract Cowpeas [Vigna unguiculate (L) Walp] as a summer cover crop have the potential to provide N to a cool‐season crop. The objectives of this study were to evaluate two cowpea cultivars grown as a cover crop to supply N for forage rye (Secale cereale L.) and to document cowpea N and C contributions to the soil. The 2‐yr study was conducted at the Texas A&M AgriLife Research Center at Overton on a Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult) during 2014–2016. Treatments were arranged in a split‐plot design with four replicates with cover crop as the main plot and N rate as subplot. Cover crop treatments included ‘Combine’ (COM) and ‘Iron and Clay’ (IAC) cowpeas and summer fallow. In late summer, cowpeas were incorporated as green manure, and four rates of fertilizer N were applied to rye. Total 2‐yr cowpea biomass incorporated as green manure was similar at 4,596 kg ha−1 and 5,058 kg ha−1 for IAC and COM, respectively. Cowpea was not effective as a green manure crop at providing N for rye biomass. Total soil N showed no difference (P ≥ .34) between cowpea entries or N rate within a soil depth. Each N rate increased rye biomass (P

The meals after oil extraction from many oilseed crops have nutrition and biofumigation potential for land application. Oilseed meal (SM) from the dedicated bioenergy crop Jatropha curcas were implicated to contain compounds that have antibacterial properties on some soil pathogens. However, little is known about its effect on non-targeted soil microbial community, especially on fungi. SM from Camelina sativa contains moderate level of glucosinolates (GLS) and was under studied. To investigate soil fungal community responses to jatropha and camelina SMs, we conducted a lab based microcosm study, amending soil with 1% SMs of jatropha, camelina, flax, and biomass of wheat straw. Fungal community abundance and structure were analyzed based on the ITS region using qPCR and tag-pyrosequencing. Microbial functional changes were examined by community level physiological profile (CLPP) using Biolog assay. Both SMs from jatropha and camelina showed biofumigant properties and inhibited fungal proliferation. Jatropha SM significantly altered soil fungal community structures with lower fungal biodiversity and higher Chaetomium composition. Camelina SM amended soil promoted Fusarium proliferation. CLPP indicated sequential hierarchy for C metabolism in the oilseed-amended microcosms was generally complex C > phosphate-associated C > carboxylic acids > carbohydrates > amines > amino acids. No significant difference in CLPP was detected due to the type of SM treatment. Our data indicate that both SMs of jatropha and camelina have biofumigant properties and can differentially impact soil microbial communities, and the changes were relatively persistent over time. Microbial functional patterns on the other side were not impacted by SM type. Our study revealed biofumigant and nutritional influence of SMs from dedicated biofuel plants on soil microbial community. This information will help properly using jatropha and camelina SMs for pathogen control while minimizing their negative impacts on non-target microorganisms. However, further studies in the field are demanded to investigate their influences in real practice.

The limited availability of soil phosphorus to plants under salinity stress is a major constraint for crop production in saline soils, which could be alleviated by improving mycorrhizal and soil microbial interactions. This study investigated the effects of Funneliformis mosseae (Fm) inoculation on phosphorus (P) availability to Sorghum bicolor, and alkaline phosphatase (ALP) activity and gene abundance (phoD) in a P-deficient naturally saline soil. A greenhouse study was conducted in order to compare the experimental treatments of Fm inoculated vs. control plants grown in saline soil with and without (sterilized soil) native microbial community. A separate hyphosphere (root-free) compartment was constructed within the mycorrhizosphere and amended with phosphate. After four weeks of transplanting, shoot, roots, mycorrhizosphere, and hyphosphere samples were collected and analyzed for soil and plant P concentrations, root colonization, and abundance of ALP and phoD. The results showed significantly higher colonization in Fm-inoculated treatments compared to uninoculated. Plant available P concentrations, phoD gene abundance and ALP activity were significantly reduced (p < 0.05) in sterilized-hyphosphere as compared to unsterilized in both Fm-inoculated and uninoculated treatments. Inoculation with Fm significantly increased the plant P uptake (p < 0.05) when compared to uninoculated treatments, but only in the plants gown in unsterile mycorrhizosphere. It can be concluded that inoculation of Fm increased root colonization and the uptake of P by sorghum plant in saline soil and native microbial community interactions were critical for increasing bioavailable P concentrations. These beneficial interactions between plants, mycorrhizae, and native microbes should be considered for soil fertility management in saline soils.

The meals from many oilseed crops have potential for biofumigation due to their release of biocidal compounds such as isothiocyanates (ITCs). Various ITCs are known to inhibit numerous pathogens; however, much less is known about how the soil microbial community responds to the different types of ITCs released from oilseed meals (SMs). To simulate applying ITC-releasing SMs to soil, we amended soil with 1% flax SM (contains no biocidal chemicals) along with four types of ITCs (allyl, butyl, phenyl, and benzyl ITC) in order to determine their effects on soil fungal and bacterial communities in a replicated microcosm study. Microbial communities were analyzed based on the ITS region for fungi and 16S rRNA gene for bacteria using qPCR and tag-pyrosequencing with 454 GS FLX titanium technology. A dramatic decrease in fungal populations (~85% reduction) was observed after allyl ITC addition. Fungal community compositions also shifted following ITC amendments (e.g., Humicola increased in allyl and Mortierella in butyl ITC amendments). Bacterial populations were less impacted by ITCs, although there was atransient increase in the proportion of Firmicutes, related to bacteria know to be antagonistic to plant pathogens, following amendment with allyl ITC. Our results indicate that the type of ITC released from SMs can result in differential impacts on soil microorganisms. This information will aid selection and breeding of plants for biofumigation-based control of soil-borne pathogens while minimizing the impacts on non-target microorganisms.

Microbial reduction of toxic hexavalent chromium (Cr(VI)) in-situ is a plausible bioremediation strategy in electron-acceptor limited environments. However, higher [Cr(VI)] may impose stress on syntrophic communities and impact community structure and function. The study objectives were to understand the impacts of Cr(VI) concentrations on community structure and on the Cr(VI)-reduction potential of groundwater communities at Hanford, WA. Steady state continuous flow bioreactors were used to grow native communities enriched with lactate (30 mM) and continuously amended with Cr(VI) at 0.0 (No-Cr), 0.1 (Low-Cr) and 3.0 (High-Cr) mg/L. Microbial growth, metabolites, Cr(VI), 16S rRNA gene sequences and GeoChip based functional gene composition were monitored for 15 weeks. Temporal trends and differences in growth, metabolite profiles, and community composition were observed, largely between Low-Cr and High-Cr bioreactors. In both High-Cr and Low-Cr bioreactors, Cr(VI) levels were below detection from week 1 until week 15. With lactate enrichment, native bacterial diversity substantially decreased as Pelosinus spp., and Sporotalea spp., became the dominant groups, but did not significantly differ between Cr concentrations. The Archaea diversity also substantially decreased after lactate enrichment from Methanosaeta (35%), Methanosarcina (17%) and others, to mostly Methanosarcina spp. (95%). Methane production was lower in High-Cr reactors suggesting some inhibition of methanogens. Several key functional genes were distinct in Low-Cr bioreactors compared to High-Cr. Among the Cr resistant microbes, Burkholderia vietnamiensis, Comamonas testosterone and Ralstonia pickettii proliferated in Cr amended bioreactors. In-situ fermentative conditions facilitated Cr(VI) reduction, and as a result 3.0 mg/L Cr(VI) did not impact the overall bacterial community structure.

There is a critical need to investigate how land application of dedicated biofuel oilseed meals affects soil ecosystems. In this study, mustard (Brassica juncea) and flax (Linum usitatissimum) seed meals and sorghum-sudangrass (Sorghum bicolor) were added to soil at levels of 0, 1, 2.5, and 5% (w/w). Both the type of amendment and application rate affected soil organic C, total C & N, and C & N mineralization. Mustard meal amendment initially inhibited C mineralization as compared to flax, but >50% of mustard and flax organic C was mineralized within 51 d. Nitrogen mineralization was similar for flax and mustard, except for the 2.5% rate for which a lower proportion of mustard N was converted to nitrate. The mustard meal greatly impacted microbial community composition, appearing to select for specific fungal populations. The potential varying impacts of different oilseed meals on soil ecosystems should be considered when developing recommendations for land application.