Cover Crop Mulches for No-till
Organic Onion Production
By: Emily Volmer (ervollme@ncsu.edu) M.S. Candidate, North Carolina State University
Cover-cropping is an important practice in sustainable organic production of annual vegetables because it replenishes soil organic matter and helps maintain fertile, healthy soil. As mulches, cover crops can conserve moisture, smother weeds, encourage soil life, improve soil structure, and prevent erosion. Grass mulches like foxtail millet are particularly useful for controlling weeds because of their slow rate of decomposition. Leguminous plants such as cowpea capture and fix nitrogen and improve soil fertility.
Winter annual cover crops like rye, hairy vetch, and crimson clover are common varieties and are typically managed by undercutting, mowing or rolling for no-till planting of warm season vegetables. However, their life cycle is not well-matched with production schedules for early spring vegetables. This two year project explores the use of summer annual cover crops—those that are susceptible to winter kill—as mulches for no-till fall planting of onions.
The first year of the project took place on CEFS' Farming Systems Research Unit. Results are preliminary at this time but have raised a number of intriguing ideas about the efficiency of summer annual cover crops in fall cropping systems. Year two of the study is taking place on the Small Farm Unit. Grown separately and as mixtures, foxtail, millet and cowpea cover crops will succumb naturally to cold weather. Onion transplants will then be planted into the residues in the fall. Onions will receive various quantities of organic nitrogen fertilizer in the form of soybean meal. Soil mineral nitrogen will be measured during onion growth from November to June to determine the quantity and timing of nitrogen release from the cover crop residues. The effectiveness of cover crop mulches to control weed growth will also be evaluated.
production of annual vegetables because it replenishes soil organic matter and helps maintain fertile, healthy soil. As mulches, cover crops can conserve moisture, smother weeds, encourage soil life, improve soil structure, and prevent erosion. Grass mulches like foxtail millet are particularly useful for controlling weeds because of their slow rate of decomposition. Leguminous plants such as cowpea capture and fix nitrogen and improve soil fertility. 
Grown separately and as mixtures, foxtail, millet and cowpea cover crops will succumb naturally to cold weather. Onion transplants will then be planted into the residues in the fall. Onions will receive various quantities of organic nitrogen fertilizer in the form of soybean meal. Soil mineral nitrogen will be measured during onion growth from November to June to determine the quantity and timing of nitrogen release from the cover crop residues. The effectiveness of cover crop mulches to control weed growth will also be evaluated.