POSTANTHESIS NITROGEN LOSS FROM CORN

Published research has shown relatively large amounts of NH3 being lost from aboveground vegetation during grain development for various grain crops For corn (Zea mays L.), maximum net N accumulation usually occurs during early reproductive development (R1-R3) and a subsequent decline is often observed. Two recently completed N fertilizer recovery studies on irrigated corn utilizing isotopic techniques were re-examined to quantify post-anthesis N losses from aboveground biomass of irrigated corn under different N regimes. These studies were conducted at different sites, in different years, with fertilizer rates ranging from 50 to 300 kg N ha-1. Measured losses of labeled N from aboveground plant material ranged from 7 to 34 kg N ha-1. Isotopic dilution suggests that apparent real N losses from aboveground biomass ranged from 45 to 81 kg N ha-1, assuming there is no selectivity for N source (i.e., N-15 vs. N-14). Plant N losses accounted for 52 to 73% of the unaccounted-for N in N-15 balance calculations. Failure to include direct plant N losses when calculating an N budget leads to overestimation of losses from the soil by denitrification, leaching, and ammonia volatilization. Proper accounting for volatile plant N losses may improve management strategies that affect N fertilizer use efficiencies.