Residual inorganic soil nitrogen in grass and maize on sandy soil

Nitrogen (N) remaining as inorganic ('mineral') soil N at crop harvest (N-minH) contributes to nitrate leaching. NminH data from 20 (grass) and 78 (maize) experiments were examined to identify main determinants of N-minH. N-rate (A) explained 51% (grass) and 34% (maize) of the variance in N-minH. Best models included in addition crop N-offtake (U), offtake in unfertilised plots (U-0), and N-minH in unfertilised plots (N-minH,N-O) and then explained up to 75% of variance. At low N-rates where apparent N recovery p keeps to its initial value P-ini, N-minH keeps to its base level N-minH,N-0. At N-rates that exceed the value A(crit) where rho drops below rho(ini), N-minH rises above N-minH,N-0 by an amount proportional to (rho(ini) - rho)A. About 80% of (rho(ini) - rho)A was found as N-minH, in grass as well as in maize. The fraction (1 - rho(ini))A does not appear to contributeto N-minH at low N-rates (A <= A(crit)) or at high N-rates (A > A(crit)). (c) 2006 Elsevier Ltd. All rights reserved.