Nitrogen in Sugarbeet Tops and the Growth of a Subsequent Wheat Crop

Abstract

AbstractNitrogen 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 Cl 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.