Modeling nitrate leaching and organic-C build-up under semi-arid cropping conditions of N India

Nitrate leaching, overall N balance, and organic-C build-up in a semi-arid agro-ecosystem in NW India was estimated from the results of a long-term manurial trial with farmyard manure (FYM) and mineral-N fertilizer in operation since 1967 at the Research Farm of CCS Haryana Agricultural University, Hisar, India. The model LEACHN was calibrated for the wheat-growing period November 2000 to April 2001 and the leaching of nitrate during this period was predicted to 48 kg N ha -1 without mineral-N fertilization and 59kg N ha -1 with addition of 120 kg mineral-N fertilizer, both with the addition of 15 t ha -1 FYM. The N balance for the simulation period showed that the 120 kg N ha -1 -mineral N fertilization compared to zero mineral N, both plus FYM, resulted in only slightly higher crop uptake, leaching losses, and NH 3 volatilization, and a negligible increase of N in organic matter. The largest amount remains as an additional build-up of mineral N in the profile (84.3kg N ha -1 ) which is prone to losses as ammonia or nitrate. The model was used to simulate organic-C build-up with FYM and a decrease of organic C without FYM for a period of 33 y (1967-2000). The simulated C build-up to about 0.1 gkg -1 agreed very well with the measured values and showed that additional mineral-N fertilization will not have any significant effect on organic-C content. Simulations with the assumption of no FYM application showed a gradual decrease of organic C from its starting value of 0.046 gkg-1 in 1967 down to almost half of this. This agreed well with the observed organic-C values of 0.028 g kg-1 as measured for unmanured plots.