2021 Volume 66 Pages 31-38
Regarding soybean cultivation in the southwestern warm region, cultivation tests, in which four topdressing treatment plots with different timings and amounts and non-topdressing plot were set up, were conducted in order to examine the effect of nitrogen topdressing using slow release nitrogen fertilizer after beginning of the flowering stage on the soybean growth and yield. The above ground dry matter weight, the above ground nitrogen uptake and the total number of pods increased in the treated plots with topdressing compared to the non-topdressing plot after the pod setting period. The dry grain weight and the amount of grain nitrogen in the mature stage showed large values in the early group for the topdressing timing and in the large group for the topdressing amount. However, the grain nitrogen content showed large values in the late topdressing group. Although the total number of pods was the largest in the contribution to the grain yield, no clear tendency was observed in the total number of pods due to the difference in the topdressing timing and the topdressing amount. From these results, the effect of increasing yield by topdressing using slow release nitrogen fertilizer after the beginning of flowering stage was observed in soybean cultivation in the southwestern warm region. In addition, it was suggested that topdressing at the beginning of flowering stage is effective when the purpose is to secure the dry matter weight, nitrogen uptake and the grain yield, and that topdressing 2 weeks after the beginning of flowering stage was effective when the purpose is to increase the grain nitrogen content.