Abstract
To examine the effect of the method of nitrogen fertilizer application (incorporation into plow layer, surface layer application and side dressing) on the recovery rate of applied nitrogen and its distribution in rice plant, we investigated the absorption of 15N-labeled (ammonium sulphate) in Hokkaido Kamikawa Agric.Exp.Stn. (Humic Brown Lowland soil). The average recovery rate of nitrogen incorporated into the plow layer (4, 8, 12, 16 g N m-2) ranged from 32 to 41%. The distribution of applied nitrogen in the plants fertilized with 8 g m-2 incorporated into the plow layer was 36.5% to leaves and stems, 63.5% to ears and 45.4% to polished rice. The surface layer application method (combined with incorporation into plow layer) of nitrogen reduced the recovery rate and protein content of polished rice and yield. The side dressing combined with incorporation into the plow layer increased the recovery rate of nitrogen and grain yield compared with incorporation of all of the fertilizer into the plow layer. However, side-dressed nitrogen was mainly absorbed by the plants before the flag leaf stage, and was less distributed to ear and grains resulting in a low protein content of polished rice. The recovery rate of nitrogen incorporated into the plow layer ranged from 2 to 4% in the next year, and from 1 to 2% in the third year. The amount of applied fertilizer nitrogen remaining in the soil after the third year of harvest was about 20% on the average. We concluded that the combination of side dressing and incorporation into the plow layer could be a valuable method for the production of low protein-content rice in high yields.
