Akio Sumi

Effect of Fertilizer and Fixed Nitrogen on the Water Use Efficiency of Genge (Astragalus sinicus L.)

Abstract To compare the effect of fertilizer nitrogen (N) and fixed N on water use efficiency (WUE), we measured the cumulative evapotranspiration (ΣET) and total dry matter mass (DM) of genge growing in plant growth chambers. When regulating NH4–N application at 11 levels ranging from 0 – 315 mgN flask −1, N concentration of the genge rose from 0.7% to 3.9% as fertilizer N application was increased. Although both DM and ΣET changed on a quadratic curve, their relationship approximated a single regression line, regardless of N concentration. The effects of rhizobial inoculation of genge samples along with NH4–N application rates of 0, 10.5, 105, and 252 mgN flask−1 were also tested. The samples with application rates of 0 and 10.5 mgN flask −1, where both nodulation and fixed N application were confirmed, had lower WUE than un-inoculated samples. These results suggest that the impact on WUE is much greater in fixed N than in fertilizer N.