Sugarbeet Growth as Affected by Wheat Residues and Nitrogen Fertilization

Little is known about how low-N, mature wheat (Triticum aestivum L.) straw and high-N, postharvest volunteer wheat growth from the previous year influence N fertilizer requirements for sugarbeet (Beta vulgaris L.). This 2-yr field study examined how wheat straw (3.36 and 6.72 Mg ha^-1; 3.5 g N kg^-1 in 2000 and 8.0 g N kg^-1 in 2001), preflowering wheat residues (2.1 to 4.2 Mg ha^-1; 29.1 to 44.7 g N kg ^-1), and urea (0 to 225 kg N ha^-1), fall-applied and incorporated, affected sugarbeet growth. The previous crop was wheat, and wheat straw was removed from the experimental sites subsequent to the grain harvest. Sugar yields were decreased 10% by application of 3.36 Mg ha^-1 straw and 25% by 6.72 Mg ha^-1 straw in 2000. The corresponding 2001 sugar decreases were 13 and 19%, respectively. Application of 45 kg ha^-1 urea N largely overcame the detrimental effect from 3.36 Mg ha^-1 straw but only partially overcame the detrimental effect from 6.72 Mg ha ^-1 straw in both experiments. Plant N, petiole NO₃-N, and soil inorganic N (NH₄-N + NO₃-N) data all indicated that incorporation of low-N mature wheat straw decreased availability of soil N, probably due to net N immobilization associated with straw decomposition. In contrast to mature wheat straw, application and incorporation of high-N, preflowering wheat residues increased recoverable sugar yields in both years. Removal of straw after a wheat crop reduces the N fertilizer requirement for a subsequent sugarbeet crop.