Review of corn yield response under winter cover cropping systems using meta-analytic methods

Extensive research on the use of winter cover crops (WCC) under different agricultural practices in the USA and Canada has shown both negative and positive effects on subsequent corn (Zea mays L.) yield. These contrasting results determine the need for a comprehensive quantitative review. The objective of this study was to use metaanalytic methods to summarize and quantitatively describe the effects of WCC on corn yield based on peer-reviewed published research. Thirty-six studies were included in the analysis representing different regions of the USA and Canada under different agricultural practices (i.e., species, fertilization, kill date, tillage, etc.). The effect-size used to compare studies was the response ratio, calculated as yield of corn following WCC over yield of corn following no cover. Biculture WCC increased corn yield by 21%, but there is greater variation due to the small number of studies in this group. Overall, grass WCC neither increased nor decreased corn yields and this response was not dependent on the use of N fertilizer. Legume WCC increased corn yield by 37% when no nitrogen (N) fertilizer was applied and this benefit decreased with application of N fertilizer.