With the advent of agricultural cover crops, it is clear that they offer numerous benefits beyond their primary role as ground cover. The versatility of cover crops that provide ecosystem services is well documented, including a range of soil enhancement and agricultural advantages. These green guardians work tirelessly to enhance the physical, chemical and microbial properties of the soil, strengthen soil structure, enhance the essential nutrients for moisture retention and cycling, while also inhibiting weed proliferation. Therefore, it is important to study the versatility of the above-mentioned cover crops while optimizing their selection and management of sustainable agricultural practices, especially focusing on the impact on soil water and nitrogen dynamics stored in semi-arid areas.
USDA-ARS lead investigator Dr. Partson Mubvumba conducted a study to better understand the nuances between cover crop types between colleagues from A&M University of Texas, Dr. Paul Delaune and Dr. Frank Hons. Their work was published in the peer-reviewed journal Soil Safety. The study was conducted at Texas A&M Agrilife Research, where they have been using a farm-free system, but they introduced routine farming as a comparison more than a decade ago. Soil treatment includes different farming methods, growing crops and grazing. These methods were tested by a cover crop mixture consisting of legumes and non-glucose to see how they affect wheat yield and soil health. Dr. Mubvumba and his team collected soil samples at different times throughout the study and analyzed various soil components, including nitrate, ammonium, carbon, nitrogen and stored soil water.
“The results presented here indicate that crops grazing in semiarid eco-regional areas with limited resources are a potentially viable land management option, where integrated crop and livestock production is a common practice,” concluded Dr. Mubvumba. Although The biomass of cover crops is reduced by half each year, but grazing does not consistently affect the measured soil parameters compared to ungrazed cover crops. This suggests that grazing can reduce the production costs of the crop, making its implementation more feasible while still bringing the relevant benefits to sustainable production.
Grass-covered crops in the mixture improve the physical properties of the soil and moisture recharge capacity, ultimately resulting in a yield comparable to the wheat yields treated in fallow (non-covered crops) under certain years. Furthermore, cover crop biomass effectively circulates nutrients in the soil system, and organic nitrogen contributes significantly more significantly compared to long-term till-free practices without crops.
However, Dr. Mubvumba and his team observed that the utilization of cover crops could deplete limited soil nitrogen and water resources, and could affect subsequent wheat crops if the collapse of cover crop residues is slow. “The crop mixture used for multiple species covers was formulated as legumes to mitigate nitrogen immobilization, but the poor performance of legumes due to precipitation instability leads to low nitrogen content, resulting in low carbon to nitrogen crop residue ratios of low carbon to nitrogen ,” Dr. Mubvumba observed. Despite the addition of nitrogen fertilizer, this resulted in nitrogen fixation and lower wheat yields. Therefore, choosing the right legume species suitable for a specific region is crucial to success.
Different crop types exhibit different carbon-to-nitrogen ratios, which determine their decomposition rate and nutrient cycle kinetics. Careful orchestration of cover crop selection, seeding rate, termination time and management techniques are key to leveraging its full potential and ensuring sustainable agricultural practices. However, the selection and management of crop species requires subtle balancing behaviors, depending on various factors such as environmental conditions, agricultural practices and economic considerations. Especially in semiarid regions with sparse rainfall, the effect of cover crops on soil moisture retention and nitrogen circulation becomes critical. Overall, this study, conducted by Dr. Mubvumba and colleagues, highlights how cover crops can help store carbon in soil, prevent nitrogen loss and nitrogen reaching our waterways, and support sustainable agricultural practices. Farmers considering using cover crops should pay close attention to rainfall forecasts, check soil nitrogen levels, and plan carefully to optimize soil health and ensure long-term productivity.
Journal Reference
Partson Mubvumba, Paul B. Delaune, Frank M. Hons. “Impact of grazing summer cover crop mix on carbon-nitroso cycle, soil water and wheat yield.” Soil Safety, 2023.
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