Abstract
Sources of the variation of wheat yield in paddy-upland rotational fields (rice-wheat-soybean) were examined during the wheat seasons from 2002 through 2004 to evaluate the possibility of the variable rate management that implements the site-specific input of agricultural materials, e.g. fertilizer and seed, in proportion to the variation of these sources in the field for maximum yield. The number of panicles was the largest source of variation contributing to wheat yield among the three yield components (number of panicles, thousand-grain weight and number of ripened grain per panicle). This result proposed the number of panicles as the criterion of variable rate management for maximizing the yield. The number of panicles was effected by the seeding rate via the number of establishment, the amount of nitrogen accumulated in aboveground biomass at spikelet-initiation stage and the number of stems, and in addition, it seemed to be effected by the soil moisture percentage at seeding via the emergence depth. Therefore, the proper management of variable rate seeding in proportion to the soil moisture percentage on dried soil basis at seeding in the field may be able to control the number of panicles in the field to bring the adequate average yield. This variable rate management may control 42.7% of the controllable proportion to total variation of wheat yield in the field.
