Abstract
The differences in growth of corn varieties were examined on the first year field and eighth year field after conversion from ill-drained paddy field. Three varieties, P3715, Takanewase and G4553 were grown in 1981 under three conditions of nitrogen level, i.e. none, standard and heavy (1.5 fold) applications on each year field. The yields and contents of total nitrogen (T-N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were investigated in each organ at the stages of heading and yellow-ripening. Since the growth and yield of corn varieties under the no-nitrogen application plots on the first year field after conversion were markedly poor, that the characters related to growth and yield were statistically analyzed only between the standard and heavy nitrogen application plots. Length and weight of ear, yield and TDN yield on the first year field were lower than those on the eighth year field, significantly, but culm length and diameter were not affected. In Takanewase, the rate of growth depression on the first year field was greater than that of the other varieties, i.e. evidently short in ear length and low in ear ratio. Many dead leaf blades were also observed at the yellow-ripening stage. Inorganic contents, especially T-N, P and K in leaf blades on the first year field were lower than those on the eighth year field in the all three varieties. In Takanewase, the contents of T-N, P, K and Ca in leaf blades were particularly low, but P, K, Ca and Mg were high in stems. The pattern of nutrient absorption of Takanewase was differed from that of other varieties, such as it decreased nitrogen absorption amount at the yellow-ripening stage in stead of the heading stage on the first year field. The growth and yield of the no-nitrogen application plots on the first year field were much lower than that of the nitrogen applied plots and that of the no-nitrogen application plots on the eighth year field. The yield increase of the heavy nitrogen application on the first year field was greater than that on the eighth year field, which shows that the yield on the first year field after conversion depends strongly on the application of nitrogen.
