The relationships between the amounts of nitrogen fertilizer applied and taken up by sugarbeet crops and the concentrations of sugar and α-amino-N in the storage root were examined using data obtained from fertilizer-response trials on different soils in the UK and Belgium between 1974 and 1985. On unmanured mineral soils, crop uptakes of N without fertilizer ranged from 65 to 190 kg/ha and increased linearly with the amount of fertilizer N applied. On organic soils or mineral soils that had received large applications of organic manure, crop uptakes of N were very large (295–383 kg/ha) and were not increased by applications of fertilizer N.
The amino-N contents of harvested beet increased with crop N uptake. The distributions of crop N to the storage root and of storage-root N to amino-N differed, especially in manured, diseased and drought-affected crops. Greater proportions of crop N were present in the storage roots of manured crops than in conventionally fertilized crops, and more of the storage-root N was present as amino-N in crops affected by virus yellows or drought than in healthy, unstressed crops.
The fresh weight concentrations of sugar in the storage root also differed between sites and years but were not consistently reduced by applications of fertilizer N at individual sites. However, when compared across sites, concentrations were negatively correlated with crop N uptakes and the amounts of N in storage roots. This was because particular crops grown on mineral soils with large applications of manure or on organic soils had large N uptakes and exceptionally low concentrations of sugar.
The physiological implications of these relationships between N uptake and amino-N and sugar accumulation are discussed.