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Washington State University - Puyallup Organic Farming Systems and Nutrient Management

Cover Crops


Cover crops are used to supply fresh organic matter to soils, improve soil structure, fix nitrogen, cycle nutrients, protect soil from erosion, and as a tool to manage weeds and other pests. Choice and management of cover crops depends on which benefits are most important, and on the cropping system.

Our research has been focused on fall-planted and relay-planted cover crops.  We have evaluated the effects of different fall-planted rye vetch blends, planting dates, and incorporation dates on ground cover, winter weed competition, and nitrogen supply to the subsequent crop.  Relay planting is the planting of cover crops between rows of the cash crop during the summer or early fall. Our relay cover crop research was focused on establishment, survival, ground cover, and N supply capability of legumes interseeded into standing vegetable crops.  Recent research is focused on cover crop management in reduced tillage organic systems.

Cover Crops Photo Essays:

Interseeded cover crop demonstrations over various dates:

Organic Systems Experiment over various dates:


Nitrogen Contribution of Rye-Hairy Vetch Cover Crop Mixtures to Organically Grown Sweet Corn (PDF-Online).  Lawson, A., A. M. Fortuna, C.G. Cogger, A.I. Bary, and T. Stubbs.  2012.  Renew. Ag. Food Sys. 28:59-69.  Available on CJO doi:10.1017/S1742170512000014.

Influence of Seeding Ratio, Planting Date, and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance Under Organic Management (PDF-Online). Lawson A., C. Cogger, A.Bary, A. Fortuna. 2015. PLoS ONE 10(6): e0129597. doi:10.1371/journal.pone.0129597

Cover Crop Effects on Light, Nitrogen, and Weeds in Organic Reduced Tillage (PDF-Online) Wayman, S., C.G Cogger., C. Benedict, D.P. Collins, I Burke, and A.I Bary. 2015. Agroecology and Sustainable Food Systems, 39:647-665. doi: 10.1080/21683565.2015.1018398

The Influence of Cover Crop Variety, Termination Timing, and Termination Method on Mulch, Weed Cover, and Soil Nitrate in Reduced-Tillage Organic Systems (PDF-Online). Wayman, S. C. Cogger, C. Benedict, I. Burke, D. Collins, and A. Bary. 2014. Renewable Agric Food Sys. doi: