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. Core Ideas Legume cover crop N accumulation ranged from 15 to 169 kg N ha–1. Corn yield after legume crops was not affected by poultry litter application rate. Legume cover crops provide opportunity to reduce poultry litter application rates.