Cover Crops and Water Quality

Abstract

Core Ideas Cover crops increase time to runoff start and reduce runoff sediment loss. Grass cover crops can be effective at reducing nutrient leaching. Cover crops may have limited effect on reducing losses of soluble nutrients. Use of cover crops may reduce the amount of herbicide used by suppressing weeds. Reducing runoff sediment and nutrient loss as well as nutrient leaching from croplands is a high priority to mitigate nonpoint‐source pollution (NPSP) of water sources, maintain soil fertility, and improve overall soil and water quality. Adoption of cover crops (CCs) can be a reemerging strategy to address these concerns. This article reviews the state‐of‐knowledge of CC impacts on water quality parameters, discusses factors that affect CC impacts, and identifies research areas. The review indicates that CCs increase time to runoff start by 10 to 40 min, and reduce both runoff volume by 10 to 98% and sediment loss by 22 to 100%. The few studies indicate that CC effects on total and dissolved nutrients in runoff are not generally significant. Grass CCs such as rye (Secale cereale L.) can reduce nitrate leaching between 18 and 95%. Cover crop effectiveness can be in this order: nitrate leaching ≥ sediment > runoff > dissolved nutrients in runoff, indicating that CCs are highly effective at reducing nutrient leaching but can have limited effects on reducing transport of dissolved nutrients. More measured and modeled data evaluating CC effects on water quality under different CC management factors including planting and termination dates, CC species, CC mixtures or single species, and tillage systems are needed. Additionally, specific data on CC belowground biomass and their relations with soil erodibility are scanty. In conclusion, CCs can reduce runoff, sediment loss, and nitrate leaching, but may have smaller effects on reducing dissolved nutrients in runoff.