Legume cover crops reduce poultry litter application requirements in organic systems

Organic farmers are challenged by increasing soil P levels resulting from the use of manure to meet cash crop N needs. The use of a legume cover crop may address this challenge. In a 2-yr study at three organic production sites in Maryland, we examined the combination of a winter annual legume cover crop (hairy vetch, crimson clover, Austrian winter pea, and a no-cover control) at three poultry litter (PL) application rates (to meet the N requirement of corn, to replace P removed by corn grain harvest, and a no-PL control). Cover crop biomass varied by site and by year, ranging from about 600 to 6100 kg ha^–1 for crimson clover. Cover crop N accumulation ranged from 15 to 169 kg N ha^–1. Corn yields, which ranged from 2.9 to 14.2 Mg ha^–1, tended to be lowest in the control (0 PL) no-cover treatments and similar in the N-based and P-based treatments irrespective of the cover crop species. These results indicate that when legume cover crops are used, PL can be applied at a P-replacement rate on sites with a history of PL application to meet crop production and environmental stewardship goals.