Effect of cover crop termination timing on pools and fluxes of inorganic nitrogen in no-till corn

Authors: OTTE, BRIANA - University Of Maryland; Mirsky, Steven; Schomberg, Harry; DAVIS, BRIAN - University Of Maryland; TULLY, KATHERINE - University Of Maryland

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2019
Publication Date: 8/30/2019
Citation: Otte, B., Mirsky, S.B., Schomberg, H.H., Davis, B., Tully, K. 2019. Effect of cover crop termination timing on pools and fluxes of inorganic nitrogen in no-till corn. Agronomy Journal. 111:1-11. https://doi.org/10.2134/agronj2018.10.0699.
DOI: https://doi.org/10.2134/agronj2018.10.0699

Interpretive Summary: Cover crops are used to provide agroecosystem benefits like reduced soil erosion and enhanced nitrogen (N) cycling. Cereal rye, a widely used cover crop in the US, can provide N to a following crop. However, timing of its termination (when it is killed prior to corn planting) may influence the quantity of N cycled. Delaying cereal rye termination increases overall N scavenging and typically results in greater cover crop biomass. We evaluated impacts of termination timing on N availability and corn performance (growth and yield) at Beltsville, MD. We expected larger quantities of biomass for cereal rye terminated 7 days (late) compared to 40 days (early) before corn planting. This was observed only the second study year when there was sufficient spring rainfall to promote cereal rye growth. Similar to other studies, higher rates of decomposition and N release were measured from early- compared to late-terminated cereal rye which was related to lower C:N ratio of the former. Delaying termination increased biomass but reduced overall residue quality, which plays a large role in driving the rate of residue decomposition and N release. Slower decomposition rates observed for late-terminated cereal rye appeared to balance N release with corn N demand which can buffer against N losses. As the northeastern US is expected to experience greater precipitation (during spring and summer growing seasons) due to climate change, we conclude that planting cereal rye cover crops will help retain and more efficiently cycle N while maintaining corn yields. This information will be useful to scientists devising strategies for cover crop integration into cropping systems.

Technical Abstract: Cover crops are used across the world to enhance nitrogen (N) cycling and provide agroecosystem benefits. Nitrogen scavenging capacity of cover crops during winter months is well documented, but less has been done to document the implications of cereal rye management on water and nitrogen availability in the subsequent growing season. We characterized cover crop termination management effects on cereal rye (Secale cereale L.) biomass quantity and quality; decomposition, and N release rates; soil inorganic N and soil water dynamics; and corn (Zea mays L.) performance (biomass and yield) at Beltsville, MD. The three cover crop management scenarios were: no cover crop; early-termination (~40 d before corn planting); and late-termination (~7 d before corn planting). Cereal rye biomass remaining after termination was tracked during and after the corn growing season (24-week). Low spring precipitation in 2016 resulted in similar amounts of cereal rye biomass following early- and late-termination. However, the late-terminated cereal rye had lower quality (greater carbon:N) in both years leading to slower decomposition and N release rates. Over the corn growing season, late-terminated cereal rye plots consistently had the smallest soil N pools, suggesting more efficient N cycling (better synchrony of N release from cover crop residues with corn N demand) than early-terminated cover crops. Corn yields were smallest following the late-terminated cereal rye in 2016, but there was no difference in yields among cover crop treatments in 2017. Overall, we determined that planting cereal rye cover crops and delaying termination until later in the season will help retain and efficiently cycle N while maintaining corn yields.