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.