Influence of anhydrous ammonia rate and band spacing on irrigated corn grain yield and band persistence

Several processes determine the efficiency of applied N fertilizers. In the case of anhydrous ammonia (AA), the rate of nitrification may determine the persistence of the AA retention zone. Moreover, nitrification is of particular interest in the N use efficiency of production systems because it transforms a relatively immobile cation (NH$\sb4$-N) to a highly mobile anionic form (NO$\sb3$-N) which is prone to leaching losses and denitrification. The implications of these losses have agronomic, economic and environmental significance. Field experiments were conducted (1991 and 1992) over four locations in Nebraska to evaluate the effect of AA rate and band spacing on irrigated corn grain yield, persistence of AA bands and subsequent residual soil-N distributions. The fertilizer treatments were (i) N rates (56, 112, 168 and 224 kg ha$\sp{-1}$) plus check (0 N), (ii) N sources (AA and NH$\sb4$NO$\sb3$ (AN)) either knifed at 38, 76 and 152 cm spacing (KS) or broadcast without incorporation (AN). Four N concentration levels (19, 37, 75 and 149 kg N ha$\sp{-1}$ knife$\sp{-1}$) were selected and sampled to evaluate the persistence of AA bands. Residual soil-N (NH$\sb4$-N and NO$\sb3$-N) was sampled in the fall. The experiment was arranged in a randomized complete block and factorial treatment design with four replications. The narrow spacing ($\u3c$76 cm KS) performed better than the wide (152 cm KS) for grain yield although their superiority was confined to coarse textured soils where direct volatile losses were apparently high in the wider spacing and high N rates. Apparent nitrification was overall faster in 1991 averaging 33 days half-life compared to 66 days in 1992 at the highest concentration (149 kg ha$\sp{-1}$ knife$\sp{-1}$) of applied N. Residual soil-N distributions in the fall did not indicate any consistent differences in NH$\sb4$-N or NO$\sb3$-N content of soils regardless of N source and rate. This was consistent with nitrification patterns of AA bands indicating that AA concentration affected the persistence of the bands although apparently not enough to influence residual effects