Abstract
We reported previously that the accumulated amount of absorbed nitrogen increased linearly during the fruit growing stage in the Japanese pear (Pyrus pyrifolia Nakai) 'Kousui.' In the present study, the influence of nitrogen top dressing at the fruit growing stage was investigated in 'Kousui' to develop an efficient method for nitrogen application. With application of 15% of the total amount of nitrogen at both the early (early May) and middle stages (early June) of fruit growing, the fruit weight was increased significantly as compared with cultivation without top dressing. Even with a reduction in amount of nitrogen to 20%, the fruit with the top dressing grew as large as that given the standard amount for Ibaraki Prefecture. In plots with the top dressing, the NO_3-N concentration in the soil solution at the rhizosphere (depth, 20cm) was higher than that without top dressing during the fruit growing stage. These results indicated that the method of nitrogen top dressing conforms to the nitrogen accumulation characteristics of 'Kousui' reported previously, and it is possible to reduce the nitrogen level by 20% as compared to the standard amount using this method. The NO_3-N concentration in the groundwater of the experimental field where the standard amount of nitrogen had been applied ranged from 4.9 to 9.5mg L^<-1>, which was below the environmental standard of 10mg L^<-1>.
