Cover Crops Research Articles

Effects of Cover Crops on Weed Suppression in the Inter-Row Spaces of Citrus Orchards

Abstract A multi-year study was carried out at two citrus groves with mature trees in Southwest Florida in the United States to evaluate the effects of cover cropping on the citrus inter-row as a sustainable weed management strategy in the Florida citrus production system. Two cover crop (CC) mixes (legume + nonlegume species and only non-legume species) were compared with a no-CC grower standard management (GSM) that utilized the herbicide paraquat for weed suppression in the citrus tree inter-row spaces. We gathered data on the biomass and density of both cover crops and weeds, during the spring and summer/fall CC planting seasons throughout the study years. Both mixes of CCs effectively reduced weed density in the citrus inter-row by 58 to 99% (P<0.05), depending on the growing season and study locations, compared to GSM. Additionally, there were no significant differences observed between the different CC mixes. Similarly, both CC mixes reduced the weed biomass by 95 to 99% (P<0.05) in the citrus inter-row compared to the GSM. However, weed suppression by CCs varied between growing seasons, mainly due to differences in germination and establishment of the CCs in each season.

Carbon and Nitrogen Mineralization of Common Organic Amendments in Olive Grove Soils

Cover crops (CC), pruning residues (PR), and olive mill pomace (OP) are common amendments to enhance soil quality in olive groves; however, there is limited information on the dynamics of carbon (C) and nitrogen (N) during their decomposition under varying conditions. In this laboratory decomposition experiment, we assessed the C and N mineralization of CC, PR, and OP at application rates of 2 and 5 mg C g−1 in soils with varying organic C levels, both with and without the addition of NO3−. The results indicated that C and N mineralization patterns varied significantly between amendments, although the predicted remaining C after one year was similar for CC and PR (46.7–48.9%) and slightly lower for OP (40.0%). Soil organic carbon level did not affect remaining amendment-C. The addition of N accelerated the decomposition rate of labile C by 15% but slowed down that of the recalcitrant C another 13%, with no significant effect on remaining C. Conversely, increasing the C dose led to a 13% overall reduction in amendment-C mineralization across all combinations of factors. CC decomposition released between −8 and 31% of the amendment-N by day 130, while PR and OP showed net N immobilization. Therefore, CC residues contribute to both C sequestration and N availability, while PR and OP residues can improve N retention in the olive groves while also contributing to C sequestration.

Cover crop rotation suppresses root-knot nematode infection by shaping soil microbiota.

Cover crop integration into grain crop rotations is a promising strategy for mitigating nematode-induced diseases in agriculture. However, the precise mechanisms underlying this phenomenon remain elusive. Here, we first assessed the impact of five commonly used cover crops on the suppression of rice root-knot nematodes (RKNs). We then chose ryegrass as a model to explore the mechanistic basis of the suppression effect. Contrary to expectations, while ryegrass rotation significantly enhances soil fertility, this increased fertility has minimal impact on RKN suppression. Furthermore, neither integrated ryegrass residues nor root exudates exhibit direct toxicity towards RKNs. We demonstrated that ryegrass rotation primarily suppresses RKNs by enriching beneficial soil microbiota. By complementing with isolated bacteria strains, we further demonstrated that ryegrass-enriched bacteria not only directly reduce RKN infectivity and preference, but also activate plant immunity via the OsLRR-RLK-MAPK-WRKY-JA cascade, thereby diminishing RKN infection. Our study highlights the crucial role of soil microbiota in plant-nematode interactions, challenging conventional views on the direct effects of cover crops in nematode suppression. It offers a mechanistic understanding of the regulation potential and action modes of cover crops in mitigating nematode diseases, providing valuable insights for sustainable agriculture.

Using Legume-Enriched Cover Crops to Improve Grape Yield and Quality in Hillside Vineyards

Natural covering (NATC) has spread on hillside vineyards of central Italy as a replacement for tillage to reduce soil erosion, although it increased nitrogen and water needs. Therefore, in the current context of global warming, using cover crops (CCs) that require less water and provide nitrogen becomes crucial. The effects of two low-competition legume-enriched CCs in a rainfed hillside vineyard—a perennial legume–grass mixture (PLGM) and an annual legume cover crop of Trifolium alexandrinum (ALTA)—were compared with NATC over three years. PLGM and ALTA provided good levels of soil coverage, slightly lower than NATC, which had a negligible presence of legumes. PLGM and ALTA, due to low competition, enhanced vine vigor, resulting in thicker and wider canopies (as indicated by total leaf area and leaf layer number), higher pruning weight, and increased yield. PLGM and ALTA led to good qualitative levels, with higher grapes acidities, lower pH and total soluble solids content and, additionally, significantly higher yeast assimilable nitrogen content. In conclusion, implementing low-competition legume species in CCs is an effective tool to avoid soil erosion in a climate change scenario, leading to increased productivity, higher acidity, and improved nitrogen content in the grapes.

Drought Resistance of Cover Crops and Grain Crops in Oxisols in Southern Brazil

Drought Resistance of Cover Crops and Grain Crops in Oxisols in Southern Brazil

Maize Morphophysiological Changes Modulated by Cover Crops Rotation in Northeast Brazil

Cover crops have gained attention due to their potential benefits for the soil and physiological performance of subsequent crops. This study aimed to evaluate the physiological and productive aspects of maize grown in succession to cover crops in northeastern Brazil. A randomized complete block design with four repetitions was employed, in which the treatments consisted of the following cover crops: sunn hemp, spectabilis, pigeon pea, Brachiaria sp., jack bean, millet, and fallow. Physiological aspects and production components of maize were evaluated at the tasseling (VT) and smooth grain (R3) phenological stages. Millet cover increased carotenoid content in maize leaves by up to 78% at R3. Maize grown after pigeon pea, millet, and Brachiaria sp. showed up to 42% greater CO2 assimilation efficiency compared to jack bean. Carboxylation efficiency increased by up to 34% in maize grown after millet and Brachiaria sp., while water use efficiency improved by up to 76% in maize after sunn hemp and pigeon pea at R3. Sunn hemp, spectabilis, and jack bean reduced soil temperature by 2 °C compared to fallow. The highest maize yield was observed after jack bean, with an 8% increase over fallow. These findings demonstrate the benefits of incorporating cover crops into maize cultivation systems in the semi-arid region of Brazil.

The LTAR Croplands Common Experiment at Upper Mississippi River Basin-Ames.

Agricultural systems evolve from the interactions of climate, crops, soils, management practices (e.g., tillage, cover crops, nutrient management), and economic risks and rewards. Alternatives to the corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] (C-S) cropping systems that dominate in the US Midwest may provide more sustainable use of resources, reduce the documented environmental impacts of current C-S systems, and improve production efficiency and ecosystem services. Innovative management practices are needed to offer producers options to increase farm resilience to variable weather conditions and offset negative environmental impacts. In response to this need, the Upper Mississippi River Basin Long-Term Agroecosystem Research network site at Ames, IA, established a cropland experiment in 2016 to investigate an alternative crop management system that includes reduced tillage, cover crops, and right source, right rate, right time, and right place (4R) nitrogen (N) management. The experimental site is located on the Iowa State University Kelley Research Farm in Boone County, IA. Crop, soil, air, and tile drainage water measurements are made throughout the year using published methods for each agronomic and environmental metric. Our goal is to provide quantitative information to farmers, consultants, agribusiness partners, and state and federal agencies to help guide decisions on the effective use of alternative management practices. Future changes in experimental treatments will adopt a knowledge co-production approach whereby researchers and stakeholders will work collaboratively to identify problems, implement research protocols, and interpret results.

Improving Cover Crop Interseeding in Northern Climates

AbstractExtensive research has found that cover cropping can increase the overall health of agricultural systems by scavenging excess nutrients, increasing water infiltration, reducing surface runoff, increasing biodiversity, and building organic matter. Furthermore, cover cropping can help enhance the benefits of other farming practices such as no‐till planting, creating synergies that increase farm financial and environmental sustainability. In northern climates, there are significant challenges to establishing cover crops due to the short growing window following corn silage harvest. The authors of this article share their experiences, challenges, and successes of integrating cover crops into northern climates. Earn 0.5 CEUs in Crop Management by reading this article and taking the quiz at https://web.sciencesocieties.org/Learning‐Center/Courses.

Modeling soil organic matter changes under crop diversification strategies and climate change scenarios in the Brazilian Cerrado

In Brazil, land conversion and agricultural management have historically accounted for the largest share of the country's greenhouse gas (GHG) emissions, with the Cerrado region being one of the most affected areas. Although cropping diversification has been proposed as a potential strategy to mitigate GHG emissions through soil organic carbon (SOC) sequestration, the long-term effects of these systems in the Cerrado are unknown. The DayCent model was used to simulate the impact of crop diversification and tillage on SOC dynamics until 2070 (∼50 years), including common crop succession systems and crop rotations associated with cover crops under climate change scenarios. First, we calibrated and evaluated the DayCent model using plant and soil observations from three sites in the region, where Pearson coefficients (r values) ranged from 0.50 to 0.94 (calibration sites) and 0.53–0.99 (validation site) for crop yields, SOC, and nitrogen. We then used the model to investigate how cropping systems and climate interact to control SOC levels. Results indicate that SOC stocks would decrease under the long-term (∼50 years) soybean-cotton succession, regardless of soil management (-0.04 to −0.17 Mg C ha−1 year−1). Crop diversification with crop rotation and cover crops (i.e., millet, ruzigrass, sunn hemp) had the highest SOC accrual potential (∼0.71 Mg C ha−1 year−1), resulting in SOC stocks of up to 130 Mg C ha−1 by 2070. Ruzigrass, either single or intercropped with maize on crop succession systems, showed substantial potential for SOC sequestration (∼0.55 Mg C ha−1 year−1) and could be a viable strategy if implementing more complex rotations is not feasible. The SSP2 – 4.5 and SSP5 – 8.5 climate change scenarios increased SOC stocks by 6.3 and 8.2 % in SOC across treatments by 2070, respectively. Results suggest that diversified cropping systems are a promising strategy for increasing SOC sequestration, and they offer valuable guidance for enhancing current management practices in the region.

Mapping of soil erosion risk in Ezeagu Local Government Area of Enugu State, Nigeria

This study centres on mapping soil erosion risk in Ezeagu Local Government Area of Enugu State, Nigeria. A multi-criteria research design was adopted in carrying out this study by using remote sensed images, topographic, soil and rainfall data. K Factor, R Factor, P Factor, K Factor and Digital Elevation Model were generated. SWAT model was used to generate surface runoff and sediment yield and AHP model were used to identify and map levels of soil erosion risk in the study area. Loamy sandy soil with a K Factor value of 0.23 – 0.34 (t h MJ-1 mm-1) and loam soil with a K factor Value of 0.08 – 0.14 (t h MJ-1 mm-1) dominates the study area. The organic matter contents for all the soils were rated low with an average measured organic matter of 0.97 (%). The rainfall erosivity factor (R-factor) results showed variations across the study area from 1029.295 to 1343.092, 1343.092 to 1589.713, 1589.713 to 1744.922, 1744.922 to 1965.777, and 1965.777 to 2060.864 MJ mm ha year-1, h-1 year-1. Areas with dense vegetation had lower P-factors indicating better protection against erosion, while areas under cultivation, especially those with poor management practices and without cover crops show higher P-factors. Almost all the area has a moderate (0.5-0.6) C factor which means moderate protection, areas with higher protection (0.6-1) C factor occupied a small portion towards the east while patches of low C factors are found scattered in the north, west northwest, south and eastern part of the study area. The eastern part of the study area are more susceptible to soil erosion with value ranging from 3.2-5.8, 5.9-9.9 and 10.0-19. Slope steepness and slope length is lower in the northern, western and south-west of the study area. Areas with annual soil loss between 0 to 10 grams, 10 to 20 grams and 30 to 40 grams dominates the northern, western and southern parts of the study area. The erosion risk map depicts that very low-risk area coverage of 24.06%, low risk covers 20.29%, moderate risk occupies 17.75% and high risk erosion risk covers 21.30% while very high risk occupies 16.61% of the total area. This study recommends terracing and gabions in areas identified at risk of erosion, promotion and adoption of agronomic soil conservation methods of mulching, cover cropping and planting plants to enhance soil stability and reduce erosion.

Cover crop characteristics modulate amount and timing of nitrogen supply of fertilized sugar beet (Beta vulgaris L.) in temperate climate

For temperate climate, there is little information on the effects cover crops grown in fall (CCs) on the nitrogen (N) supply for next year’s sugar beet (SB). Four field trials were conducted on silty soils to establish the CC N effect (Neff) compared to bare fallow separately for the periods sowing-summer and summer-autumn harvest. Biomass characteristics of radish (Raphanus sativus L.), spring vetch (Vicia sativa L.), saia oat (Avena strigosa Schreb.), and winter rye (Secale cereale L.) CCs before winter, soil mineral nitrogen in spring (SMN), and SB N accumulation and sugar yield (SY) were measured. In the period sowing-summer, characterized by a high SB N demand, Neff of overwintering, high biomass yielding rye CC was negative up to -50 kg N ha-1 at three site/years and varied around zero for the other CCs except vetch, for which Neff was positive. At SB autumn-harvest, Neff was negative up to -100 kg N ha-1 except for vetch in one trial. SY was lowest after rye CC. Regression analyses indicated a negative impact of CC biomass, C:N ratio and the difference in SMN between fallow (high SMN) and CCs (low SMN) on Neff. To conclude, if CCs yield a high amount of biomass surviving until spring and thus remove SMN from the soil which otherwise remains available for SB, early season mineralization of CC biomass N can be too low to ensure a N supply sufficient for maximum SB yield. Choosing leguminous CCs or early termination of CCs might alleviate this constraint.

Investigating the Role of Cover-Crop Spectra for Vineyard Monitoring from Airborne and Spaceborne Remote Sensing

The monitoring of grape quality parameters within viticulture using airborne remote sensing is an increasingly important aspect of precision viticulture. Airborne remote sensing allows high volumes of spatial consistent data to be collected with improved efficiency over ground-based surveys. Spectral data can be used to understand the characteristics of vineyards, including the characteristics and health of the vines. Within viticultural remote sensing, the use of cover-crop spectra for monitoring is often overlooked due to the perceived noise it generates within imagery. However, within viticulture, the cover crop is a widely used and important management tool. This study uses multispectral data acquired by a high-resolution uncrewed aerial vehicle (UAV) and Sentinel-2 MSI to explore the benefit that cover-crop pixels could have for grape yield and quality monitoring. This study was undertaken across three growing seasons in the southeast of England, at a large commercial wine producer. The site was split into a number of vineyards, with sub-blocks for different vine varieties and rootstocks. Pre-harvest multispectral UAV imagery was collected across three vineyard parcels. UAV imagery was radiometrically corrected and stitched to create orthomosaics (red, green, and near-infrared) for each vineyard and survey date. Orthomosaics were segmented into pure cover-cropuav and pure vineuav pixels, removing the impact that mixed pixels could have upon analysis, with three vegetation indices (VIs) constructed from the segmented imagery. Sentinel-2 Level 2a bottom of atmosphere scenes were also acquired as close to UAV surveys as possible. In parallel, the yield and quality surveys were undertaken one to two weeks prior to harvest. Laboratory refractometry was performed to determine the grape total acid, total soluble solids, alpha amino acids, and berry weight. Extreme gradient boosting (XGBoost v2.1.1) was used to determine the ability of remote sensing data to predict the grape yield and quality parameters. Results suggested that pure cover-cropuav was a successful predictor of grape yield and quality parameters (range of R2 = 0.37–0.45), with model evaluation results comparable to pure vineuav and Sentinel-2 models. The analysis also showed that, whilst the structural similarity between the both UAV and Sentinel-2 data was high, the cover crop is the most influential spectral component within the Sentinel-2 data. This research presents novel evidence for the ability of cover-cropuav to predict grape yield and quality. Moreover, this finding then provides a mechanism which explains the success of the Sentinel-2 modelling of grape yield and quality. For growers and wine producers, creating grape yield and quality prediction models through moderate-resolution satellite imagery would be a significant innovation. Proving more cost-effective than UAV monitoring for large vineyards, such methodologies could also act to bring substantial cost savings to vineyard management.

Does a native and introduced cover crop species differ in their ability to suppress weeds? A study in a table grape vineyard

This study compared the weed suppression ability of a native cover crop species phacelia (Phacelia tanacetifolia), an introduced cover crop species rye (Secale cereale L.), and a no cover crop (herbicide‑managed) system in a vineyard. Cover crops were sown in the interrow spaces of the grapevine rows. Percent weed cover after the cover crop termination was lower in the interrow of the phacelia than the no cover crop plots. During the cover crop growing season, phacelia suppressed weeds more than rye. However, the weed seedbank of the cover crop plots was greater than that of the no cover crop plots.

Mapping predicted biomass in cereal rye using 3D imaging and geostatistics

Abstract Cover crops are becoming an increasingly important tool for weed suppression. Biomass production in cover crops is one of the most important predictors of weed suppressive ability. A significant challenge for growers is that cover crop growth can be patchy within fields, making biomass estimation difficult. This study tested ground-based structure-from-motion (SfM) for estimating and mapping cereal rye (Secale cereale L.) biomass. SfM generated 3D point clouds from red, green, and blue (RGB) videos collected by a handheld GoPro camera over five fields in North Carolina during the 2022 to 2023 winter season. A model for predicting biomass was generated by relating measured biomass at termination using a density–height index (DH) from point cloud pixel density multiplied by crop height. Overall biomass ranged from 320 to 9,200 kg ha−1, and crop height ranged from 10 to 120 cm. Measured biomass at termination was linearly related to DH (r2 = 0.813) through levels of 9,000 kg ha−1. Based on independent data validation, predicted biomass and measured biomass were linearly related (r2 = 0.713). In the field maps generated by kriging, measured biomass data were autocorrelated at a range of 5.4 to 42.2 m, and predicted biomass data were autocorrelated at a range of 3.4 to 12.0 m. However, the spatial arrangement of high- and low-performing areas was similar for predicted and measured biomass, particularly in fields with greatest patchiness and spatial correlation in biomass values. This study provides proof-of-concept that ground-based SfM can potentially be used to nondestructively estimate and map cover crop biomass production and identify low-performing areas at higher risk for weed pressure and escapes.

Long-term effects of agronomic practices on winter wheat yield and NUE in dryland regions of USA and China: a long-term meta-analysis

Dryland agriculture is fundamental to global crop production and vital to food security. Conservation tillage is extensively practiced in USA wheat cultivation. Meanwhile, the adoption of conservation tillage by Chinese farmers is limited. This meta-analysis compared the yield and nitrogen use efficiency (NUE) between conservation tillage and conventional tillage (CT) with different types of cropping systems, mulching methods, levels of nitrogen fertilizer (NF), and addition of manure. The meta-analysis presented that conservation tillage at high-NF enhanced the yield and NUE, and reduced the yield and NUE at low-NF, compared to CT. The interaction of conservation tillage with leguminous cover crops (LCC) and manure application increased the yield and NUE at low-NF, compared to CT. Non-leguminous cover crops (NLCC) increased the yield and NUE under high-NF than low-NF. The interaction of conservation tillage with management practices showed that the no-tillage (NT) with leguminous cover crops (LCC) significantly increased wheat yield by 58% and NUE by 47% under low-NF compared to CT. However, increasing the rate of NF did not increase the yield under such interaction. Cropping systems, mulching types, and manure application mainly determined the effects of conservation tillage on wheat yield and NUE. The adverse impact of CT on yield and NUE could be alleviated with the application of LCC and manure under moderate NF. We demonstrate that adding LCC and manure have a generally substitutive relationship with N fertilizer, resulting in a significant increase in wheat yield and NUE at low-NF doses as at high N fertilizer dosages. Therefore, based on the obtained results, moderate NF with LCC and manure application is recommended for growing winter wheat in dryland regions of the USA and China.

No-Till and Crop Rotation Are Promising Practices to Enhance Soil Health in Cotton-Producing Semiarid Regions: Insights from Citizen Science

This on-farm study was conducted to assess the impact of six prevalent crop management practices adopted by growers in West Texas on various indicators of soil health. This study is a part of a citizen science project, where we collaborated with cotton growers who helped with standardized sample and data collection from 2017 to 2022. This project aimed to identify soil management practices that increase carbon sequestration, enhance biological activities, and improve overall soil health. We monitored soil moisture, soil organic matter (SOM), inorganic nitrogen (NH4+-N and NO3−-N) and other exchangeable nutrients, and soil microbial abundances as obtained via fatty acid methyl ester (FAME) in 85 fields, incorporating different management practices during the cotton growing season. In our study, volumetric moisture content (VWC) was increased by no-till, irrigation, and crop rotation, but the addition of residue decreased VWC. No-till, irrigation, and crop rotation increased SOM, but a cover crop decreased SOM. No-till and residue retention also increased microbial biomass carbon (MBC). Tillage, irrigation, and crop rotation influenced the abundance of the main microbial groups, including bacterial, fungi, and arbuscular mycorrhizal fungi (AMF). Additionally, water content, SOM, and microbial abundances are correlated with clay percentage. Our results indicate that no-till and crop rotation are the two most crucial soil management approaches for sustainable soil health. As such, implementing both no-till and crop rotation in the cropping systems has the most promising potential to increase the soil resilience in dryland cotton production in semiarid regions, thereby helping growers to maintain cotton production.

Surface soil sampling underestimates soil carbon and nitrogen storage of long-term cover cropping

Cover cropping is a promising management practice for soil health and climate change mitigation by improving soil organic carbon (SOC) and total nitrogen (TN) stocks. However, limited studies focused on deeper soil layers (>30 cm depth) where soil C is more stable than that in surface soil (≤30 cm depth). Here, deep soil sampling was conducted in a 15-year cover cropping experiment, in a horticulture-grain system on sandy loam soil. The SOC and TN stocks were expressed on an equivalent soil mass basis using a cubic spline model. Overall, long-term cover cropping had significantly greater SOC and TN stocks by 22 % (95 %CI: 5–43 %) and 26 % (95 %CI: 6–49 %), respectively in the 0–120 cm depth, compared to no cover cropping. Additionally, the mean SOC and TN sequestration rate (0–30 cm depth) was 0.53 Mg C ha−1 yr−1 and 0.06 Mg N ha−1 yr−1, respectively. However, if only 0–15 cm depth was evaluated, long-term cover cropping did not significantly affect SOC and TN stocks. These results indicated that shallow sampling (<15 cm depth) may not provide comprehensive information on the effect of long-term cover cropping on soil C and N storage. To better understand the mechanism of bulk soil C and N storage, we investigated their distribution between particulate and mineral-associated organic matter pools (POM and MAOM). We found POM pool was the main store of bulk SOC and TN stocks in surface soils while it was the MAOM pool in deeper soil layers, without soil texture change with soil depth. These findings indicated that soil C and N sources for bulk SOC and TN accrual differed in surface and deeper soils. Our study demonstrated that long-term cover cropping can facilitate SOC accumulation in the soil below 15 cm deep, which calls into question carbon capture protocols that focus on shallow soil depths.

The Impact of Winter Cover Crops on Soil Nematode Communities and Food Web Stability in Corn and Soybean Cultivation.

There is increasing adoption of winter cover crops (WCCs) in corn and soybean production in Canada, primarily to reduce erosion and increase soil organic matter content. WCCs have the potential to influence nematode communities by increasing free-living nematodes and decreasing plant-parasitic nematodes or vice versa. However, the mechanism by which WCCs change nematode community assemblages still remains a key question in soil food web ecology. We tested the hypothesis that the long-term use of rye (Secale cereale), barley (Hordeum vulgare) and oat (Avena sativa) as monocultures or mixtures promotes nematode communities and improves overall soil health conditions compared to winter fallow. The results from this study revealed that the use of WCCs generally promoted a higher abundance and diversity of nematode communities, whereas plant parasitic nematodes were the most abundant in winter fallow. Moreover, the mixtures of WCCs had more similar nematode communities compared to rye alone and winter fallow. The structure and enrichment indices were higher with WCCs, indicating higher nutrient cycling and soil suppressiveness, which are signs of healthy soil conditions. Furthermore, WCCs significantly reduced the populations of root lesion nematode Pratylenchus, although their numbers recovered and increased during the main crop stages. Additionally, mixtures of WCCs promoted the highest abundance of the stunt nematode Tylenchorhynchus, whereas winter fallow had a higher abundance of the spiral nematode Helicotylenchus during the fallow period and the main crop stages. The results show that the long-term use of cover crops can have a positive impact on nematode communities and the soil food web, but these changes depend on the type of WCCs and how they are used.

Agricultural practices influence soil microbiome assembly and interactions at different depths identified by machine learning

Agricultural practices affect soil microbes which are critical to soil health and sustainable agriculture. To understand prokaryotic and fungal assembly under agricultural practices, we use machine learning-based methods. We show that fertility source is the most pronounced factor for microbial assembly especially for fungi, and its effect decreases with soil depths. Fertility source also shapes microbial co-occurrence patterns revealed by machine learning, leading to fungi-dominated modules sensitive to fertility down to 30 cm depth. Tillage affects soil microbiomes at 0-20 cm depth, enhancing dispersal and stochastic processes but potentially jeopardizing microbial interactions. Cover crop effects are less pronounced and lack depth-dependent patterns. Machine learning reveals that the impact of agricultural practices on microbial communities is multifaceted and highlights the role of fertility source over the soil depth. Machine learning overcomes the linear limitations of traditional methods and offers enhanced insights into the mechanisms underlying microbial assembly and distributions in agriculture soils.

Reduced nitrogen rate sustains malt barley yield and quality in malt barley‐pea rotation

AbstractRotational benefit of pea (Pisum sativum L.) may reduce N fertilization rate and sustain malt barley (Hordeum vulgare L.) yield and quality in the malt barley‐pea rotation. This study examined the effect of cover crop [oat (Avena sativa L.) cover crop vs. none] and N fertilization rate (0, 40, 50, 60, 70, and 80 kg N ha−1) on malt barley growth, yield, and quality in the malt barley‐pea rotation from 2012 to 2019 in the northern Great Plains. Cover crop biomass yield and N accumulation were greater in 2016 than other years. Compared to fallow, malt barley plant density with cover crop was 9%–13% lower from 2013 to 2015, but 10% greater in 2017. Malt barley straw yield was 38% greater in 2017 and grain yield 15%–39% greater in 2017 and 2018, but grain plumpness was 5%–10% lower in 2014 and 2017 with than without cover crop. Increasing N fertilization rate linearly increased grain yield and N uptake, but reduced grain test weight and plumpness in most years. Straw N concentration and uptake and grain protein concentration varied by year. Because of the similar grain yield, protein concentration, plumpness, and test weight between 60 and 80 kg N ha−1, 60 kg N ha−1 can be recommended to sustain malt barley yield and quality in the malt barley‐pea rotation, regardless of cover crops. This helps to reduce N fertilization rate by 20 kg N ha−1 for malt barley in dryland cropping systems of the US northern Great Plains.