Abstract
The rice variety `Koshihikari' was cultivated as the early-season culture in Kyushu (west-southern district in Japan) from 1976 to 1978. The experiments were conducted at 19 plots which had different nitrogenous fertilization in all 3 years. 1) The brown rice productions were about 6t/ha in each year. But the efficiency of absorbed nitrogen on the rice grain varied with the cultivated year and the nitrogen supplied. When the efficiency of absorbed nitrogen was low, rice plant had many ears and abortive grain. 2) Strong negative correlation was observed between the efficiency of absorbed nitrogen on the rice grain and the number of ears. 3) Positive correlation was observed between iron-manganese ratio in the stem and leaf at the early stage and the efficiency of absorbed nitrogen on the rice grain, also the number of grains per head. But the number of ears, nitrogen % in the stem and leaf at heading time and the amounts of nitrogen uptake at maturing stage had negative correlation with iron-manganese ratio. 4) In the high-yielding culture of `Koshihikari,' it was a very useful method that gives priority to the increase of the number of grains per head over the increase of the number of ears. 5) I supposed the relation between the efficiency of absorbed nitrogen on the rice grain yield and the uptake of iron and manganese in the early stage was affected by the soil condition, the character of seedlings and the physiological activity of rice plant's roots.
