Result of Experiment on Planting Density of Rice Plants under the Conditions of Deep Tillage and Heavy Application of Manure and Fertilizer on Paddy Field

The experiment was carried out with variety "Ginmasari" as early season rice culture, and with variety "Kinmaze" as early planting rice culture on the well-drained paddy field of alluvial loam, in 1960. The field was divided into two blocks each differing in depth of tillage and the amount of applied cattle stable manure, with the other. As chemical fertilizer, fused magnesium phosphate and potasium chloride were added as basic dressing, without any nitrogen. To one block which was ploughed to a depth of 25 cm, manure was applied at the rate of 9 tons/10 a (0.1 ha), while the other block ploughed to a depth of 50 cm was applied at the rate of 15 tons/10 a. Besides, planting was carried out according to the following density, having 70, 105 hills, each of which consisting of 3 and 5 seedlings, and 140 hills which consisting of 4 and 7 seedlings per tsubo (3.3m2), respecitively. The result is summarized as follows: 1. During the early part of July, the period between the stage of the maximum number of tillers and the booting stage of variety "Ginmasari", and between the late stage of tillering and the stage of the maximum number of tillers of variety "Kinmaze", the rice plant showed nutrition deficiency which increased remarkably with increasing plant density. This is assumed to indicate that reasonable heavy application of manure is rational in the case of rice culture under the conditions of deep tillage, and dense planting. This phenomenon, however, got naturally disappeared after the end of July, and the rice plant of the block of 50 cm depth tillage showed growth responses indicating the existence of excessive nutrition during the ripening stage after September. 2. The yield of brown rice per 10a showed generally high production varing propo tionately to the increase of planting density; from 566∼606 kg with variety "Ginmasari" and 588∼664 kg with variety "Kinmaze" of the block of 25 cm depth tillage, and 584∼661 kg of the block of 50 cm depth tillage with variety "Kinmaze" respectively. The ratio of increasing yield to increasing plant density was low in variety "Ginmasari", and high in the case of "Kinmaze". 3. The increase of yield to increasing plant density was mainly due to the increase of total number of grains with the increase of number of panicles. The ratio of the weight of fine-husked rice to the weight of coarse-unhusked rice did not give any evidence to recognize the difference among the different planting density plots. 4. In comparing the two depth tillage blocks of the variety "Kinmaze", the block of 50cm depth tillage had a high total number of unhusked grains, and a low ratio of the weight of fine-husked rice to the weight of coarse unhusked rice.