Cover Crops and Drought: Implications for Climate Resilience.

Cover crops are a potential climate adaptation tool, helping maintain and improve soil quality in the face of more frequent extreme precipitation events.  However, it is less clear how cover cropping will impact cash crop physiology under drought, which is projected to become more frequent and severe in the Northeast US.  We report results from two years of a field study investigating maize (Zea mays) responses to drought imposed following five functionally diverse cover crop treatments.  Maize was grown in rotation with soybean (Glycine max) and wheat (Triticum aestivum) in a full-till organically managed system in central Pennsylvania.

I am testing the following hypothesis: cover crops affect the following cash crop’s physiological responses to drought by a) transpiring soil water in the spring, thereby reducing cash crop available water, and b) altering nitrogen (N) cycling and availability during the cash crop window.  Preliminary results from the first year of the study indicate that cover crop transpiration did not affect maize available water due to sufficient spring precipitation.  However, cover crop effects on N availability exerted strong control over maize drought responses.  Chlorophyll meter (SPAD) readings were used to assess maize N status.  An ANCOVA including early-season SPAD readings and drought treatment explains 74% of the variation in kernel yield for year 1 (p < 0.001), indicating that N availability during cover crop decomposition had a strong influence on yield formation under drought stress.  Cover crops with higher C:N ratio biomass exacerbated corn drought stress due to N immobilization, while cover crops with lower C:N ratio biomass mitigated drought stress due to N mineralization.  These results indicate that it will be important to optimize cover crop N management strategies to mitigate yield losses under climate change-driven drought.