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 15N 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 20KgNha−1 added yearly from 1980 to 1992, with 15N added with the fertilizer from 1980 until either 1985 or 1992. The same total amount of 15N was added with the 200 and 20KgNha−1 fertilizer: 4 and 40 15Nat.%, 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. 15N enrichment in corn and soil was higher for the 200 than the 20KgNha−1 treatment. This resulted from the rapid N mineralization–immobilization turnover that channelled N through the inorganic N pool whose 15N 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, 15N was localized in the stable pool and flushed from the more labile pools.