As cover crops emerged in agriculture, it slowly became obvious they offer a myriad of benefits beyond their primary role as ground cover. The multifunctionality of cover crops in providing ecosystem services is a well-documented phenomenon, encompassing an array of soil enhancements and agricultural advantages. These green guardians work tirelessly to enhance physical, chemical, and microbial properties of soil, fortifying soil structure, bolstering water retention, and cycling essential nutrients, while also curbing weed proliferation. Therefore, it is important to investigate the aforementioned multifunctionality of cover crops, while optimizing their selection and management for sustainable agricultural practices, particularly focusing on the impact on stored soil water and nitrogen dynamics in semiarid regions.
The lead researcher, Dr. Partson Mubvumba from USDA-ARS, conducted a study to better understand the nuanced differences between cover crop types along with his colleagues, Dr. Paul DeLaune and Dr. Frank Hons, both from Texas A&M University. Their work is published in the peer-reviewed journal, Soil Security. The study took place in Texas A&M AgriLife Research, where they have been using a no-till system, but they introduced conventional tillage as a comparison a little over a decade ago. The soil treatments included different ways of tilling the soil, planting cover crops and grazing. These methods were tested with a cover crop mix consisting of legumes and non-legumes to see how they affect wheat production and soil health. Dr. Mubvumba and his team collected soil samples at various times throughout the study and analyzed them for various soil components, including nitrates, ammonium, carbon, nitrogen, and stored soil water.
“The results presented here show that grazing cover crops under resource-limited semi-arid ecoregions is a potentially viable land management option where integrated crop and livestock production is a common practice,” Dr. Mubvumba concluded. Despite reducing cover crops biomass annually by half, grazing did not consistently affect measured soil parameters compared to ungrazed cover crops. This suggests that grazing could mitigate cover crops production costs, making their implementation more feasible while still reaping associated benefits for sustainable production.
Grass cover crops species in the mix improved physical properties and moisture recharge capacity of the soil, ultimately leading to comparable wheat yields to those following fallow (non-cover crop) treatments in certain years. Additionally, cover crops biomass effectively cycled nutrients in the soil system, contributing significantly more organic nitrogen compared to long-term no-till practices without cover crops.
However, Dr. Mubvumba and his team observed that utilization of cover crops can deplete limited soil nitrogen and water resources, potentially impacting subsequent wheat crops if cover crops residue decomposition is slow. “The multi-species cover crops mixture that was used was formulated to be dominated by legumes in order to mitigate nitrogen immobilization, but due to erratic precipitation, legume species underperformed, resulting in low nitrogen content cover crops residues with high carbon-to-nitrogen ratios,” Dr. Mubvumba observed. This led to nitrogen immobilization and lower wheat yields, despite the addition of nitrogen fertilizer. Therefore, choosing appropriate legume cover crops species tailored to specific areas could be crucial for success.
Different crop types exhibit different carbon-to-nitrogen ratios, which dictate their decomposition rates and nutrient cycling dynamics. The careful orchestration of cover crops selection, seeding rates, termination timings, and management techniques holds the key to harnessing their full potential and ensuring sustainable agricultural practices for future harvests. However, the selection and management of cover crops species entail a delicate balancing act, contingent upon various factors such as environmental conditions, agricultural practices, and economic considerations. Particularly in semiarid regions where rainfall is sparse, the impact of cover crops on soil moisture retention and nitrogen cycling becomes paramount. Overall, this study, conducted by Dr. Mubvumba and his colleagues, underscores how cover crops can help store carbon in the soil, prevent nitrogen loss, and nitrogen reaching our waterways, as well as support sustainable agricultural practices. Farmers considering using cover crops should keep an eye on rainfall forecasts, check their soil’s nitrogen levels, and plan carefully to optimize soil health and ensure long-term productivity.
JOURNAL REFERENCE
Partson Mubvumba, Paul B. DeLaune, Frank M. Hons. “Grazing summer cover crops mix impact on carbon–nitrogen cycling, soil water, and wheat yields.” Soil Security, 2023.
DOI: https://doi.org/10.1016/j.soisec.2023.100107.
