Large-scale farmer-led experiment demonstrates positive impact of cover crops on multiple soil health indicators.

Cover crops are touted for their potential agronomic and environmental benefits, and are currently incentivized through state, federal and private investment in the USA. There is a need to quantify the impact of on-farm use of cover crops at spatial (2-5 years) and temporal (regional-to-national) scales aligned with such investment programmes. Here we report soil health data from a farmer-led trial of cover crops on 1,522 strip-years, from 78 farms across 9 US states over 5 years. We found that up to 5 years of cover crop use had small but increasing impacts on four of six selected soil health indicators, with active carbon concentration responding the most rapidly. Soil texture, the length of time a field was in the trial and a farm-level random effect were also strongly related to soil health properties. Our results fit with evidence from controlled trials and suggest that the use of cover crops can begin to influence soil health within several years after adoption.