Growth and yield of sugar beet on contrasting soils in relation to nitrogen supply: I. Soil nitrogen analyses and yield

SUMMARY Nine field experiments with sugar beet in 1968–70 tested eight amounts of nitrogen fertilizer (0–290 kg N/ha) on a shallow calcareous loam (Icknield Series), on a deep sandy loam (Newport Series) and on a heavy clay loam (Evesham Series). Top soils and subsoils, sampled during autumn, winter and spring before the experiments, were analysed by several methods for available and potentially-available nitrogen. The largest increases in potentially-available mineral-nitrogen shown by incubation occurred in the calcareous loams every year in both top soil and sub-soil, and the sandy loam, particularly the sub-soil, generally produced least. Attempts to forecast the optimum nitrogen fertilizer dressing from the soil analyses were moderately successful, the best technique being anaerobic incubation of air-dry soil; the date of sampling had little effect. The optimum dressings were always between 0 and 125 kgN/ha, the calcareous loams generally needing least nitrogen fertilizer and the loamy sands most.