Simulation of nitrogen rhizodeposition and assimilation back into corn (Zea mays L.) roots

The objectives were to quantify the dynamics of N exchange between corn root and soil under field conditions and to compute the amount of N-rhizodeposition that is recycled back into corn by maturity. In a previous publication the simulation model NCSWAP/NCSOIL was used to quantify the release of organic-C from corn and its incorporation into soil organic matter. In this publication, results from the same simulations but pertinent to N are presented. The model was calibrated against measured N concentration in corn and soil and N-15 enrichment data obtained from a long-term field experiment located near St Paul, MN. Field management included rototillage, the removal of stover-residue and grain and 4 fertilizer N treatments: 200 and 20 Kg N ha(-1) added yearly from 1980 to 1992, with N-15 added with the fertilizer from 1980 until either 1985 or 1992. The same total amount of N-15 was added with the 200 and 20 Kg N ha(-1) fertilizer: 4 and 40 N-15 at.%, respectively. Corn roots released 24 % of total N uptake. This loss was mitigated by the recycling of 14 % of N-rhizodeposition into corn by maturity. N-15 enrichment in corn and soil was higher for the 200 than the 20 Kg N ba(-1) treatment. This resulted from the rapid N mineralization-immobilization turnover that channelled N through the inorganic N pool whose N-15 enrichment was fixed yearly to that of the fertilizer. Tracer N enrichment decreased more rapidly in corn than in soil from 1986 to 1992 when tracer N was no longer added with the fertilizer, and by 1992, N-15 was localized in the stable pool and flushed from the more labile pools. (C) 2004 Elsevier Ltd. All rights reserved.