Nitrogen in Sugarbeet Tops and the Growth of a Subsequent Wheat Crop
- John T. Moraghan and
- Larry J. Smith
Nitrogen in sugarbeet (Beta vulgaris L.) tops can influence the yield of subsequent small-grain crops. The objective of this field study was to determine the influence ofsugarbeet tops differing in N concentration on available soil N and plant growth. Responses of spring wheat (Triticum aestivum L.) to fall-applied urea and high-N (34.8 g N kg−1 in 1992 and 25.8 g N kg−1 in 1993) and low-N (14.8 g N kg−1 in 1992 and 12.6 g N kg−1 in 1993) sugarbeet tops were compared on two Calciaquolls in Minnesota during 1993 and 1994. Application of 135 kg N ha−1, the optimal fertilizer rate in both years, increased wheat grain yields by 1832 kg ha−1 in 1993 and by 1518 kg ha−1 in 1994. High-N sugarbeet tops, which contained 271 and 208 kg N ha−1 in the 1993 and 1994 experiments, respectively, increased grain yields by 2108 kg ha−1 in 1993 and by 1579 kg ha−1 in 1994. The corresponding responses with low-N sugarbeet tops, which contained 64 kg N ha−1 in 1993 and 85 kg N ha−1 in 1994, were 424 and 392 kg ha−1. These latter responses were equivalent to only 42 and 51%, respectively, of the 1993 and 1994 increases obtained with 45 kg urea N ha−1. Separate field experiments in fallow microplots indicated that fall-applied, high-N sugarbeet tops mineralized appreciable quantities of NO3-N by the following spring. Most of this mineralized NO3 was located in the upper 30 cm of soil. In contrast, considerable CI added in sugarbeet tops was located in both the 0- to 30-cm and 30- to 60-cm soil depths. Sugarbeet tops can reduce the N-fertilizer requirement of subsequent crops, and must be considered in relation to possible NO3 pollution of groundwater.
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