An analysis of the effects of nutrient supply on the growth of potato crops

SUMMARY Fertilizer nitrogen did not delay tuber initiation by the potato variety King Edward in the field, but slowed the early growth of tubers. Later, N hastened tuber growth and the largest amounts prolonged it. Leaf and stem growth were increased by N from an early stage. Leaf area index ( L ) reached maxima of 2.5 to 3.0 with the largest amounts of N, and 1.0 with no nitrogen: L decreased after late July, faster with increased N, and only the largest amount prolonged the life of the haulm. N increased leaf area duration ( D ) by up to 125% in both years. D was 21% greater in 1964 than 1963, and net assimilation rate in August and September was larger; consequently mean yield was 50% more in 1964. Uptake of nitrogen and N % of dry matter were increased by increasing nitrogen. The N % of tuber dry weight remained constant or increased slightly from about 2 weeks after tuber formation, while N % of the leaves and stems decreased rapidly, and much N was transferred from tops to tubers. The 1964 results suggest that tuber growth depends on continued nitrogen uptake by the plant. P and K had small effects compared with those of N. K increased leaf area duration by 9% in 1963 and 3% in 1964, and yield by 11 and 8% respectively. P increased leaf area duration by 17% and yield by 9% in 1964. K had very small effects until the end of the season, when it prolonged the period of growth. P increased growth rates of all parts of the plant up to 4 weeks from emergence, and the differences in dry weight at that time persisted to maturity but did not increase.