Carbon and Nitrogen Dynamics: Cover Crop Decomposition during the Following Cash Crop Growing Season
Nitrogen (N) loss from agriculture fields in the Corn Belt contributes to impaired waterways and the development of the “Dead Zone” in the Gulf of Mexico. It has been well established that cover crops can scavenge N, which results in a reduction of N loss via tile drainage. However, the literature suggests that increased C inputs from decomposing cover crop residue may result in N immobilization during the following cash crop growing season andnegative yield impacts. Therefore, the goals of this study were to investigate the dynamics of cover crop decomposition, C release, and N release within common midwestern crop management systems (crop rotation, cover crop selection, and tillage). A litter bag study was established at the Purdue Agronomy Center for Research and Education (ACRE). Treatments considered in this study were crop rotation: Corn/Soybean, Soybean/Corn, and Continuous Corn; cover crop species: hairy vetch (HV, Vicia villosa Roth), cereal rye (CR, Secale cereal), and mixture (20% HV, 80% CR); and tillage: No-till (NT) and reduced tillage (RT). We did not observe a significant impact of rotation on cover crop decomposition. However, cover crop species significantly impacted decomposition rate when averaged across tillage. On average, HV had greater decomposition (K = 0.00420) then treatments with CR (K = 0.00258). Specifically, HV (C:N = 11- 12) increased the rate of decomposition by 1.7 times compared to cereal rye (C:N = 15-20). Additionally, RT significantly increased cover crop decomposition across all cover crop treatments. On average, RT resulted in a 2.9 times greater decomposition rate (K) when compared to NT treatments. The impact of tillage was greatest in CR containing treatments, where RT increased the decomposition rate by 3.1 times relative to the NT treatments. Increased knowledge of factors that influence cover crop decomposition could equip farmers with knowledge to make cover crop management decisions to improve nutrient management and sustainable cash crop yields.