Predicting the amount of nitrogen fertiliser needed for sugar‐beet by soil analysis

Abstract

AbstractIn 1961–65, soils from 65 fields were analysed for potentially available nitrogen, and field experiments were carried out to measure the optimum nitrogen dressing for sugar‐beet. The soils were sampled during autumn and spring and incubated either fresh or air‐dry, all aerobically and some anaerobically. All were analysed for organic carbon and total nitrogen, and 35 were analysed for barium hydroxide‐extractable ‘glucose’.The amount of nitrogen mineralised during incubation of fresh spring‐sampled and air‐dry autumn‐sampled soils was significantly correlated to organic carbon and total nitrogen concentrations, also to the amount of ‘glucose’ extracted by barium hydroxide. Correlations were usually better with air‐dry than with fresh samples, and were also better with spring than with autumn samples.The amount of mineral nitrogen in air‐dry, spring‐sampled soil was moderately well related to the optimum nitrogen dressing (r=‐0·48**) and to the increase in sugar yield from the nitrogen fertiliser (r=‐0·49**). Although not tested on all the samples, the nitrogen mineralised during anaerobic incubation was best related (r=‐0·84**) to the optimum nitrogen dressing. The barium hydroxide‐extractable ‘glucose’ concentration was also significantly related to the optimum nitrogen dressing (r=‐0·32*) and to the increase in sugar yield (r=‐0·49**).