Does cover crop diversity increase the stability and sustainability of N dynamics in cover cropping systems? A meta-analysis
The use of cover cropping as a sustainable management tool increases biodiversity in agricultural systems both above and below ground. While different cover crop species provide specific ecosystem services that can be selected for particular management goals, the use of bicultures and multicultures is becoming more common in an effort to sustain complex systems. Due to these changes in management, new questions have arisen regarding mixtures of species diluting or amplifying the ecosystem services of individual species.
A meta-analysis was conducted to examine the effects of cover crops in monoculture and mixtures. Specifically, the meta-analysis was designed to address the effects of leguminous and non-leguminous cover crops grown in mono-, bi- and multiculture systems on leachable soil N, total soil N, crop yield, and microbial biomass. We also examined the relationships between cover crop diversity and other sustainable management practices including conservation tillage, synthetic fertilizer reduction, and pesticide inputs. A comprehensive search of the literature resulted in 68 relevant manuscripts. Effect sizes were calculated using the response ratio.
Preliminary analyses show the importance of cover crops as an effective tool for increasing supporting ecosystem services. Specifically, cover crops increase the biodiversity of agricultural systems and may increase nutrient recycling, soil stabilization, and primary production. These supporting ecosystem services can translate into increased provisioning services in the form of crop yield in some cases. The ecosystem services provided by cover crops varies by their functional group. Grasses tend to reduce soil leachable N while legumes increase total soil N by fixing nitrogen from the atmosphere. Cover crop mixtures tend to have intermediate benefits of the supporting and provisioning ecosystem services compared to monocultures. In the face of climate change, diversification of cover crop mixtures may be an important adaptation strategy to ensure cover crop establishment and primary production even under variable and extreme weather conditions. Mixtures of three or more cover crop species are becoming increasingly popular with farmers. However, there has been a limited number of papers to date that report their impacts.