Abstract
In order to clarify the yielding performance of no-tillage seeding cultivation of soybean, the effects of field locations and seeding dates on seedling establishment and yield were studied in the staple cropping area of soybean in Ibaraki pref. for five years by using a newly developed system for recording agricultural works with GPS. The failure of seedling establishment tended to occur only in the poor drainage area that received heavy rain 1-3 days after seeding under the conventional seeding condition. In contrast, the field with poor seedling establishment was observed throughout the surveyed area and irrespective of rainfall under the no-tillage seeding condition. The survey for five years revealed a negative correlation between seeding date and the soybean yield in each field, but there was no significant difference in the regression line between the no-tillage seeding and the conventional seeding. The result of multiple regression analysis showed the importance of phytopthora rot of soybean as a cause of yield loss under the no-tillage seeding condition. The relative yield compensated for yield reduction by delaying seeding was calculated by using regression equation of yield and seeding date. The field map, in which the fields were tilled with different colors according to relative yield, indicated that high-risk fields are distributed into the specific area.
