An overview of cover crop impacts on nitrogen and phosphorus losses from agricultural systems.1
Cover Crops Reduce Nitrogen Losses to the Environment
Nitrogen can be lost from agricultural fields in runoff water and groundwater. This displaced nitrogen may then travel into waterways and cause imbalances in the nutrient levels of these sensitive ecosystems. Farmers want nitrogen to remain on the land to fertilize their crops and support productive growing systems, and society as a whole doesn’t want excess levels of nitrogen in the water.
- So how can cover crops help? They scavenge soil nitrogen and prevent it from being leached, and they can provide natural sources of nitrogen to cash crops and thus reduce the amount of fertilizer needed for production.
- Cover crops reduced the amount of nitrogen leaving a field by 1% to 89%, with a median value of 48% (across 10 studies and 16 observed reductions).
What About Phosphorous?
Compared to the impact of cover crops on erosion or losses of nitrogen, the impact of cover crops on phosphorus in the field is less studied and the research inconclusive.
- Phosphorus can be transported to waterways by above- or below-ground water flows.
- Some studies report finding no significant effect of cover crops on total phosphorus losses, sometimes because the cover crops may have reduced total phosphorus losses but increased soluble phosphorus losses (often in below-ground, leachate water).
- However, reductions have been observed, showing that cover crops reduced total phosphorus loads in water samples by 15% to 92%.
- The main mechanism by which cover crops may inhibit phosphorus losses is through preventing soil loss by covering the ground and rooting to secure the soil in place.
A Systems Approach to Enhanced Water Quality and Smart Nutrient Management
When faced with problems such as eutrophication and hypoxia in our waterways, we can turn to cover crops and other conservation practices as tools to mitigate this pollution.
- With cover crops, smart fertilizer- and manure-management decisions will also decrease nutrient-loss risks.
- Continuous ground cover paired with no-till management, will successfully prevent erosion and will therefore reduce above-ground nutrient losses to the environment.
About Cover Crops
Cover crops are tools to keep the soil in place, bolster soil health, improve water quality and reduce pollution from agricultural activities.
- They include cereals, brassicas, legumes and other broadleaf species, and can be annual or perennial plants. Cover crops can be adapted to fit almost any production system.
- Popular cover crops include cereal rye, crimson clover and oilseed radish. Familiar small grain crops, like winter wheat and barley, can also be adapted for use as cover crops.
1 Unless otherwise cited, all data comes from a bibliography compiled by SARE and the University of Missouri.
Table of Contents
- Cover Crops: Selection and Management
- Cover Crops: Economics
- Cover Crops: Ecosystem Services from Cover Crops
- 10 Ways Cover Crops Enhance Soil Health
- Cover Crops at Work: Covering the Soil to Prevent Erosion
- Cover Crops at Work: Increasing Infiltration
- Cover Crops at Work: Keeping Nutrients Out of Waterways
- Cover Crops at Work: Increasing Soil Organic Matter
- Cover Crops and Carbon Sequestration
- Cover Crops Improve Soil Conditions and Prevent Pollution
- Impact of Cover Crops on Natural Enemies and Pests
- Cover Crop Impacts on Soil Invertebrates
- Cover Crop Impacts on Pollinators
- Cover Crop Effects on Deer and Other Mammalian Wildlife
- Cover Crop Effects on Songbirds and Game Birds
- Cover Crops: Environmental Impacts
- Cover Crops: Establishment
- Cover Crops: Crop Rotations
- Cover Crops: Soil and Fertility Management
- Cover Crops: Water Management
- Cover Crops: Pest Management
- Cover Crops: No-till
- Cover Crops: Miscellaneous Topics
- National Cover Crop Surveys
- Library of Images, Illustrations and Presentations
- Cover Crops: Additional Resources