Cover crops have positive and negative effects on soil properties and crop yield over a 15‐year timespan

Abstract Winter cover crops (WCC) have received much attention due to their environmental benefits, particularly improvements to soil health. However, most studies are made less than 5 years after implementation, and there is no consensus about when to soil sample to best quantify a WCC effect. We used a paired, chronosequence approach with 1–15 years since implementation of cereal rye ( Secale cereale ) as a WCC, and analyzed soils collected in spring and autumn. We measured soil bulk density, maximum water‐holding capacity, penetration resistance, pH, total carbon (C) and nitrogen (N), permanganate oxidizable carbon, microbial biomass carbon (MBC), and microbial biomass N, potentially mineralizable carbon (PMC), and potentially mineralizable nitrogen (PMN). We also analyzed maize ( Zea mays ) and soybean ( Glycine max ) grain yield. We found that WCC increased MBC and PMC by 8% each and increased PMN by 11%, regardless of time‐since‐implementation. Furthermore, sampling biological soil health indicators in the spring resulted in more positive, significant treatment effects (12%–19%) compared to sampling in the autumn, where we found no effect. WCC increased soybean yields by 7% after 8–9 years but decreased maize yield by 23% after 15 years. WCC reduced soil penetration resistance by 10% after 8–9 years but increased it by 20% after 15 years. These later contrasting results may be due to management nuances or biophysical changes in cropping systems with time. Overall, WCC have many environmental benefits, and in our study, WCC increase biological soil health indicators quickly, but yield drag and increased soil penetration resistance may occur later in WCC adoption.