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.  They may also contribute to climate mitigation through enhanced carbon sequestration.  However, it is less clear how cover cropping will impact cash crop physiology during droughts, which are 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 four functionally diverse cover crop treatments and a fallow control.  Maize was grown in rotation with soybean (Glycine max) and wheat (Triticum aestivum) in a full-till organically managed system in central Pennsylvania.

We test 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.  Results indicate that cover crop transpiration did not affect maize available water due to sufficient spring precipitation.  Both drought treatment and N status, as assessed with chlorophyll meter (SPAD) readings, affected maize yields (ANCOVA R² = 0.74, p < 0.001). Relative yield loss from drought was equivalent across cover crop treatments and the fallow control (~20%); cover cropping did not systematically improve drought resistance.  However, N-mineralizing cover crops led to superior yields under both well-watered and drought conditions.  These results suggest that, in the short term, cover crops may improve cash crop yield under drought by enhancing nutrient cycling, at least in organic systems.  Additional research is needed to better understand potential drought mitigation benefits from soil improvements associated with long-term cover cropping.