Cover crops in cereal rotations: A quantitative review

The use of cover crops in conventional agriculture is not fully accepted. This is probably due to the substantial variability in outcomes reported and is complicated by the conflation of a host of techniques under the same umbrella term, often without the appropriate benchmarking. This review addresses these issues with a quantitative synthesis of the last 11 years of research on cover crops in cereal rotations in temperate climates. Strict inclusion criteria focus the scope of the review to studies offering comparisons with an equally treated bare fallow control. Coded variables included duration, fertiliser, irrigation and tillage regime, cover and cash crop type and termination mode. The result is a quantitative review of 100 parameters covered by multiple publications, with an additional overview on 124 parameters covered by single studies. The investigated response variables range from microbiology and chemical parameters to hydrology, soil structure, weed and pest control and crop performance. Relevant trends were identified regarding strengths and weaknesses of cover cropping, with predictions formulated about the conditions necessary for their successful implementation. Additionally, trade-offs specific to cover cropping are discussed, together with the variables at play in determining the final balance of net gain or loss. The main findings are that cash crop performance is best enhanced by legume cover crops and in low-tillage regimes, and the soil biotic effects of cover crops tend to be short-lived, fading by the end of the season. Most importantly, a positive effect of cover cropping on soil carbon is potentially offset by increased GHG emissions.