Effect of soil type and nutrient management on potato after-cooking darkening

After-cooking darkening (ACD) is a common undesirable trait of potato tubers, caused by the oxidation of the chlorogenic acid-iron compound after cooking, which includes boiling, frying and dehydration. The degree of the darkening is known to be cultivar-dependent and to vary with climatic conditions. However, there is limited information on the effect of different management practices and long-term storage on ACD. In this study, we used three independent experiments to investigate the effects of soil type, different management practices and storage on the susceptibility of ACD. Experiment I compared two soil types, two planting dates, and two rates of nitrogen (N), phosphorus (P) and potassium (K) fertilization in two years for 'Russet Burbank' potato. Experiment 2 compared seven rates of N fertilization in two years for Russet Burbank and 'Shepody' potato. Experiment 3 compared five rates of K fertilization in two years on Russet Burbank potato. In general, the degree of darkening was reduced when climatic conditions and management practices resulted in conditions favorable for crop growth. The degree of ACD generally increased under drier climatic conditions, in soil that was more susceptible to drought, and with delayed planting; however, these effects were not measured in all cases. Similarly, the degree of ACD increased under N deficient conditions. However, N fertilization did not reduce darkening in all trials, and the benefit of N fertilization was not apparent as storage duration was increased. There was a small benefit to K fertilization in Experiment 3; however, K fertilization had no effect on ACD in Experiment 1. There was no effect of P fertilization on ACD. Although significant, the magnitude of the effects of soil type and management practices on ACD was small in comparison to the effects of cultivar and storage duration on ACD.