Oats ( Avena sativa L.), phacelia ( Phacelia tanacetifolia Benth.), oilseed radish ( Raphanus sativus L.), white senf mustard ( Brassica hirta Moench), kale ( Brassica oleracea L.), canola ( Brassica napus L.), turnip ( Brassica rapa L.), and yellow mustard ( Brassica hirta Moench) were evaluated for their ability to grow, accumulate leachable N, and suppress winter annual weeds during the fall following early harvest of vegetables in the northeastern United States. Brassica and phacelia cover crops planted in late August and early September produced 3000-4000 kg·ha -1 in aboveground biomass, and took up 100-120 kg·ha -1 soil N before winter killing in December. Soil inorganic N decreased in all plots through the fall of both years but concentrations in cover crop plots tended to be lower than in bare plots. Analysis of soil surface residues the following April showed that brassicas had lost a greater proportion of aboveground biomass and N during the winter than had oats in 2 years of study. How much of the loss of biomass was due to residue decomposition at the soil surface and how much was due to wind or other off-site losses is not clear. Soil inorganic N concentrations in cover crop plots tended to be higher than in bare plots the following April. Cover crop residues significantly suppressed weed growth in early spring; in several treatments, no measurable weed growth was found in the second year. These results indicate that oilseed radish, white senf mustard, and yellow mustard are well suited for use as fall cover crops in the temperate northeastern United States, but that significant biomass and N may be lost if they are left to winter kill.
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Lydia Stivers-Young (1998) studied this question.