Sugarbeet Nematode-Resistant Trap Crops for Recovery of Residual Soil Nitrates

Residual soil nitrates following the main crop harvest, if not recovered, can result in environmental problems, loss of nutrients, and reduced efficiency of irrigated sugarbeet (Beta vulgaris L.) rotations. Sugarbeet nematode (SBN)-resistant crops, also known as trap crops, grown in sugarbeet rotations to control sugarbeet cyst nematode (Heterodera schachtii Schmidt) were evaluated as cover crops (CC) for soil nitrate recovery. Cultivars of the trap crops, oil radish (Raphanus sativus L. spp. oleifera) and yellow mustard (Sinapis alba L.), as well as winter wheat (Triticum aestivum L.), were planted in early August 1996 and late July 1997 following a previous crop of winter wheat. Five nitrogen fertilizer rates were applied following soil sampling to 0.9 m. Soil samples were taken in late fall after active CC growth had ceased. Radish and mustard quickly established and produced as much as 5 to 8 Mg dry matter ha -1 . Radish and mustard above-ground biomass accumulated greater amounts of N, leaving less residual soil nitrate-N, particularly at the 0.6- to 0.9-m soil depth, than winter wheat, the standard cover crop in the region. Both trap crops winter-killed, reducing need for herbicide and lessening the likelihood of N immobilization and negative impact on the following crop.