Effects of soil‐moisture tension and fertilisers on the yield, growth and phosphorus uptake of potatoes

Main effects and interactions of nitrogen, phosphorus and potassium fertilisers and soil‐moisture tension on the growth, yield and phosphorus uptake of potatoes were studied in a field experiment. Yield, growth and nutrient uptake increases produced by applied N were interdependent with those produced by lowering soil‐moisture tension and were highly significant at all stages of growth. Increases in P uptake produced by N application at 60 lb. per acre and the lowering of moisture tension were attributed mainly to effects on root development. There was some evidence that the physiologically acid ammonium sulphate reduced the rate of fixation of applied P. Severe damage to roots and stolons by potassium chloride in the early season was reflected in reduced numbers of tubers. High N rates prolonged shoot development and delayed tuber development. Effects of potassium chloride on P uptake were small. The percentage of dry matter in tubers was considerably reduced by N and K applications and by lowering moisture tension, but was increased by applied P. Effects of applied P on P uptake were largely dependent on the presence of applied N and, as in previous work, soil‐P uptake was either depressed or unaffected by applied P. Dry matter yield/fertiliser rate curves were paraboloid in form, particularly in the early season.