Productivity and Stability of Multi‐Species Cover Crop Mixtures in the Northern Great Plains

Abstract

Core Ideas Multi species cover crops provided more stable biomass yield than single species.Grass components of cover crop mixtures were more productive than legume components.Cover crop mixtures did not use water or nitrogen differently than single species cover crops.Warm and cool season species within a functional group complemented each other.Relative LER was useful criteria to select cover crops for mixture construction. Mixed species cover crops are a relatively recent crop management method for improving soil health and cropping system sustainability. This 2‐yr study assessed the productivity and stability of cover crop mixtures with multi‐species functional groups compared with single species cover crops. Selection criteria were developed to identify suitable cover crops for a semiarid region. The study was conducted in south‐central Montana and evaluated 11 cover crop treatments which consisted of six individual species, four mixtures of these species, and a chemical‐fallow check. Biomass of cover crop mixtures was greater than single species cover crops in 2014 (p = 0.04). However, land equivalent ratio (LER) showed that cover crop mixtures did not over‐yield single species cover crops (LER ≤ 1). Cover crop mixture productivity increased where grass and taproot species were included. In contrast mixtures with legumes resulted in low overall productivity. Coefficient of variability (CV) of the functional groups was in the order of 62% > 51% > 33% for grass, taproot, and legume, respectively. Spring soil NO3–N and soil water content following cover crop mixtures were not different from single species cover crops (p > 0.05) in both years. Cover crops that produced greater biomass generally consumed more nitrogen and water. Identifying single species or mixtures with stable but acceptable biomass yield that leave greater water and soil nitrogen for the following crop is more important than maximizing biomass productivity. Species with relative LER ≥ 1 performed well within a mixture and provided a useful criterion for mixture construction.