Effects of cover crops on multiple ecosystem services: Ten meta-analyses of data from arable farmland in California and the Mediterranean

Gorm E Shackelford,Rodd Kelsey,Lynn V Dicks

doi:10.1016/j.landusepol.2019.104204

Gorm E Shackelford, Rodd Kelsey + Show 1 more

Open Access

https://doi.org/10.1016/j.landusepol.2019.104204

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Abstract

Cover crops are considered to be beneficial for multiple ecosystem services, and they have been widely promoted through the Common Agricultural Policy (CAP) in the EU and Farm Bill Conservation Title Programs, such as the Environmental Quality Incentives Program (EQIP), in the USA. However, it can be difficult to decide whether the beneficial effects of cover crops on some ecosystem services are likely to outweigh their harmful effects on other services, and thus to decide whether they should be promoted by agricultural policy in specific situations. We used meta-analysis to quantify the effects of cover crops on five ecosystem services (food production, climate regulation, soil and water regulation, and weed control) in arable farmland in California and the Mediterranean, based on 326 experiments reported in 57 publications. In plots with cover crops, there was 13% less water, 9% more organic matter and 41% more microbial biomass in the soil, 27% fewer weeds, and 15% higher carbon dioxide emissions (but also more carbon stored in soil organic matter), compared to control plots with bare soils or winter fallows. Cash crop yields were 16% higher in plots that had legumes as cover crops (compared to controls) but 7% lower in plots that had non-legumes as cover crops. Soil nitrogen content was 41% lower, and nitrate leaching was 53% lower, in plots that had non-legume cover crops (compared to controls) but not significantly different in plots that had legumes. We did not find enough data to quantify the effects of cover crops on biodiversity conservation, pollination, or pest regulation. These gaps in the evidence need to be closed if cover crops continue to be widely promoted. We suggest that this novel combination of multiple meta-analyses for multiple ecosystem services could be used to support multi-criteria decision making about agri-environmental policy.

Highlights

Cover crops are grown as an alternative to leaving the soil bare or fallow, often over the winter, and often in rotation with cash crops that are grown over the summer
We analysed the effects of cover crops on five ecosystem services: food production, soil regulation, water regulation, climate regulation, and weed control
Two or fewer publications had relevant data on pollination, pest regulation, soil biodiversity, soil erosion, sediments in water, pathogens or pesticides in water, or other forms of biodiversity

Summary

Introduction

Cover crops are grown as an alternative to leaving the soil bare or fallow, often over the winter, and often in rotation with cash crops that are grown over the summer. The remains of cover crops are often retained on the surface of the soil, and the soil is only minimally tilled or is not tilled at all. Cover crops are referred to as “green manures”. When they are used to increase soil fertility (incorporating organic carbon and nitrogen into the soil), or as “catch crops” when they are used to retain nitrogen (“catching” nitrate before it leaches out of the soil), but they are most strictly referred to as “cover crops” when they are used to cover bare soil and to reduce erosion and control weeds Cover crops have a long history that goes back over 2,000 years in Europe, where legumes were ploughed into the soil by the ancient Greeks and Romans (Pieters 1927).

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