Long‐term Nitrogen Rates and Sources Influence Sugarbeet Yield and Quality1

Abstract

AbstractApplication of excessive N to sugarbeet‐producing soils has caused a deterioration in sugarbeet (Beta vulgaris L.) quality resulting in decreased sucrose production. The objective of the present work was to determine what rates of N fertilizer would produce maximum sucrose without sacrificing quality. Influences of repeated applications of sugarbeet yield and various quality factors, in a longtime organic and inorganic N sources and rates since 1953 on irrigated sugarbeet‐small grain rotation, were investigated in 1972 at Sidney, Montana. Nitrogen treatments included barnyard manure (22.4 and 67.2 metric tons/ha), green manure (alfalfa and biennial sweetclover), ammonium nitrate (O, 56, 112, 168, 224, 336, 448, and 560 kg N/ha) and a combination organic and inorganic N treatment (67.2 metric tons barnyard manure plus 112 kg inorganic N/ha).Highest sucrose production (7.9 metric tons/ha), obtained with 22.4 metric tons/ha of manure, was accompanied by root yields of 47.5 metric tons/ha, with sucrose percentage of 16.6 and petiole NO3‐N concentration (about 6 weeks before harvest) of 663 ppm. For the inorganic N treatments, highest sucrose yield (7.6 metric tons/ha) was obtained with 112 kg/ha of N, with similar results obtained for the green manure treatments. Inorganic N rates greater than 112 kg/ha caused progressive decreases in sucrose yields, sucrose percentage, and dry matter root weights. Dry matter root/top ratios of two or greater coincide with maximum sucrose yields. Increasing the rate of organic or inorganic N applied decreased dry matter root/top ratios.Results of this study indicate that either barnyard or green manure can be used successfully as a source of N for quality sugarbeet production.