Supplemental Nitrogen Fertilizer to Soybeans : III. Effects on nitrogen fixation

[摘要] Effects of (NH4)2SO4 top-dressing at the flowering stage to soybeans were investigated in view of its nitrogen fixation and assimilation. Possibility of estimating nitrogen fixation by time course measurement of C2H2 reduction assay was also examined with top-dressed soybeans. Soybeans were grown in soil-N free sand culture. The integrated value over time course of C2H2 reduction activity was calculated and fixed. N was measured with a 15N isotope dilution technique. The conversion factor from C2H2 reduction to nitrogen fixation was determined as 1.05. Supplemental-N at flowering decreased C2H2 reduction activity of soybeans grown in pot with soil. This was mainly because nodule formation and nodule development were checked severely. Their nitrogen fixation was estimated via C2H2 reduction assay with the aforementioned conversion factor in the soybeans top-dressed. Decrease of their nitrogen fixation was considerably high. The uptake of supplemental-N, however, was larger than the decrease of nitrogen fixation due to top-dressing. This gap increased as increasing the rate of supplemental-N. At the rate of 3.78 gN/plant, for instance, the uptake was 1.60 gN/plant in favorable contrast to the decrease of fixed-N of 1.0 gN/plant. The increment in the sum of the fixed-N and absorbed supplemental-N was nearly corresponded to that in the total assimilated-N in the soybeans top-dressed. Thus, this quantitative analysis appeared to provide a good estimation of nitrogen fixation.

[学科分类] 农业科学（综合）

[关键词] Acetylene reduction;アセチレン還元;Glycine max;^<15>N;重窒素;Nitrogen;ダイズ;Nitrogen fixation;窒素固定;Soybean;窒素追肥;Top-dressing