The Alternation of Direct Sowing and Transplanting as a Counterplan for the Rice Yield Decrease due to Continuance of Direct Sowing Culture

[摘要] In some cases of direct sowing culture (direct sowing of paddy rice under upland condition) in the Kanto district, there is observed a year by year decrease in yield. The purpose of this experiment is to find a counterplan to the rice yield decrease due to the continued culture of direct sowing. This paper deals with the effect of alternation of direct sowing and transplanting on the growth and yield of direct sowing rice. 1. Better growth and better yield were given in the first year of direct sowing culture in the converted plots (converted to direct sowing culture after one or two years of transplanting one), than those in the continued direct sowing plots (direct sowing was continued more than ten years). These tendency was more apparent in well drained paddy field than in ill drained one. 2. No significant differences in the growth and yield of direct sowing rice could be found between the second year plots after converted from transplanting culture and the continued direct sowing plots. 3. Increased amount of total inorganic available nitrogen but decreased amount of nitrate nitrogen in the soil were given in the early stage of upland condition of the first year of direct sowing culture by the conversion from the transplanting culture. 4. The soil in the direct sowing paddy fields (after harvesting) was easier not only to drain but also to harrow and was favoured more porosity than in those of transplanting. Such physical properties of soil in direct sowing field was acquired in the first year after the conversion. 5. From above facts, the alternation of direct sowing and transplanting was concluded to be a promising counterplan to the rice yield decrease due to the continued direct sowing culture.

[学科分类] 农业科学（综合）