Summer Cover Crops Fix Nitrogen, Increase Crop Yield, and Improve Soil–Crop Relationships

Abstract

Impact of cover crops (CCs) on winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] yields is not well understood. We assessed crop yield and its relationships with CC‐induced changes in soil properties for a 15‐yr CC experiment in wheat–sorghum rotation at 0, 33, 66, and 100 kg ha−1 of N application in south central Kansas. Hairy vetch (Vicia villosa Roth) was used as a winter CC from 1995 to 2000, while sunn hemp (SH; Crotalaria juncea L.) and late‐maturing soybean [LMS; Glycine max (L.) Merr.] were used as summer CCs in no‐till from 2002 to 2008. Summer CCs increased crop yields particularly at low rates of N application. At 0 kg N ha−1, SH increased sorghum yield by 1.18 to 1.54 times, while wheat yield increased by 1.60 times in the first year (2004) after CC establishment relative to non‐CC plots. At 66 kg N ha−1, SH had no effects on sorghum yield, but it increased wheat yield in 2 of 3 yr. Cover crops increased soil total N pool by 270 kg ha−1 for the 0‐ to 7.5‐cm depth. Crop yield increased with the CC‐induced decrease in soil maximum compactibility (soil's susceptibility to compaction) and soil temperature, and increase in soil aggregate stability, soil organic carbon (SOC) and total N concentration, and soil water content, particularly at 0 kg N ha−1. Principal component analysis (PCA) selected soil compactibility and total N as the best yield predictors. Inclusion of summer legume CCs in no‐till fixes N, increases crop yield, and improves soil–crop relationships.