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 (∑ET) 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 ∑ET 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.