Abstract
Cover crops provide a range of well-documented benefits to growers and the environment. However, no single species can deliver all of these benefits, and hence planting mixtures is gaining increasing attention. To the best of our knowledge, there is no comprehensive review on different multi-mix strategies. This article reviews available studies on multi-mixes, focusing on temperate North America, and discusses objective criteria for selecting components of a multi-mix and what future research is needed. Very few peer-reviewed studies on multi-mixes are currently available; a diversity of species compositions is being tested with a wide range of potential benefits but also with various limitations. Selection of species in multi-mixes is based on different criteria that help improve multiple ecosystem services. An emerging concept is the importance of selecting cover crop species with functional complementarity rather than simply increasing the number of species. Based on this concept, objective criteria have been developed to select the species for a multi-mix: grower objectives/primary purpose of planting the cover crop, crop rotation and cropping system compatibility, above and belowground compatibility, complementarity of different ecosystem functions, compatibility with the growing environment, duration for cover crop growth, termination option(s) available, input/labour costs, planting equipment required, persistence/weediness, and potential net economic returns. We propose a step-wise procedure to develop effective multi-species mixtures. The number of species and their ratio in the mixtures will depend on objective criteria, and hence long-term research is required to assess different species compositions and their impacts.
Highlights
Cover crops are considered an important agroecological strategy for field crop production and soil fertility management
Winter wheat is often selected over cereal rye because of greater flexibility for grain harvest; cereal rye seed is becoming more valuable with increased demand for cover cropping seed [43]
Cover crop mixtures can be considered as a key tool for enhancing the multi-functionality, resiliency, and sustainability of cropping systems in temperate regions
Summary
Cover crops are considered an important agroecological strategy for field crop production and soil fertility management. Cover crops are any crops that are planted between periods of normal crop production with an objective of enhancing multiple ecosystem services [1,2]. Cover crops increase plant residues retained on the soil surface [4,5,6], minimize soil disturbance and erosion [7,8,9], improve soil structure and water-stable aggregates [7,8,9,10], help control various pests and weeds [11,12,13], maximize water and nutrient use efficiencies of crop production systems [11,14], and enhance net ecosystem productivity and longer-term carbon (C) sequestration. They further provide forage for livestock [12], support pollinators and beneficial insects [11,12], and reduce water and air pollution [9]
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