Role of continuous nitrogen fertilization on nutrient composition of leaves sampled at various stages of growth and on yield of yam (Dioscorea rotundata)

Abstract

Abstract White yam (Dioscorea rotundata cv. Olonko) was grown consecutively for three growing seasons, i.e. from February to October of 1975, 1976 and 1977, and treated with six levels of nitrogen, viz: 0, 40, 60, 120, 160 and 200 kg N/ha in the field. Leaf samples were taken at four stages of growth as follows: vegetative, tuber formation, tuber development and tuber maturation, and analyzed for NO3‐N, P, K, Ca and Mg. Increasing nitrogen fertilization consistently increased leaf‐NO3‐N, particularly at the vegetative stages of growth, while no consistent trend was established for leaf‐P. Leaf‐K was increased at low rate of nitrogen fertilization during tuber formation and maturation whereas leaf‐Ca increased only at tuber maturation in the presence of higher rates of nitrogen fertilization. There was a marked increase in leaf‐Mg at all stages of growth when N treatment was increased to 200 kg N/ha. A positive correlation (r = 0.84∗∗∗) was obtained for leaf‐K at the vegetative growth stage with tuber yield, while leaf‐Mg was positively correlated with tuber yield at vegetative (r = 0.46∗), tuber formation (r = 0.50∗) and tuber development (r = 0.67∗∗) stages. All other elements were negatively correlated with yield at all stages of growth. Tuber yield was highest at the 200 kg N/ha treatment.