Influence of the supply and uptake of nitrogen on the quality of potato tubers

Abstract

Potato processors impose strict quality criteria in assessing the suitability of tubers for processing. One of the more critical criteria is the dry matter concentration, [DM], in the tubers at harvest time when, generally, [DM] should exceed 20%. The [DM] of developing tubers increases with time and has been shown (Jefferies et al., 1989) to be related to the passage of thermal time qualified by soil moisture deficit at harvest. There are also reports that potato crops grown with higher N supply produce tubers with lower [DM]. The work to be reported here was conducted in two series of experiments, over the four years 1984, 1985, 1990, 1991 and using two varieties, Maris Piper and Cara. The treatments were level of nitrogen supply ranging from 0 to 240 kg N / ha and two of the experiments included split applications of (80+80) kg N / ha, applied at planting and tuber initiation. There were four replications in all experiments and all were irrigated. Harvests were taken at 10, 8, 5, and 5 intervals during the growing seasons of the four years, respectively, when full sets of growth analysis measurements were made, including [DM], [N], and the partitioning of N within the plants between tuber, leaf, and stems. The results show that rate of N-supply modifies the development of tuber [DM] by delaying the maturity of the crop. The use of thermal time removed the most of the non-linearity observed in the course of development referred to normal time. The differences in [DM] between crops given differing rates of N supply were statistically significant. Relating tuber [DM] to N-uptake in the tuber provided a useful means of combining data from the several harvests and nitrogen treatments. In contrast, there was no useful relation between [DM] and the total N-uptake. Further analysis of the results is designed to quantify the delay in maturity by reference to N-uptake rather than N-supply and to provide generality across years.