Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2004
Publication Date: 1/1/2005
Citation: Molina, J., Clapp, C.E., Allmaras, R.R., Layese, M.F. 2005. Nitrogen rhizodeposition and assimilation back into corn (zea mays l.) roots. Journal of Soil Biology and Biochemistry. 37:93-100. Interpretive Summary: The objective of this paper was to use the model NCSWAP/NCSOIL to obtain information about the soil-plant system that cannot be obtained by direct measurements and to analyze the carbon and nitrogen dynamics documented by a long-term field experiment with continuous corn. Models are crucial for organizing knowledge and predicting the behavior of complex phenomena such as carbon and nitrogen transformations in soil, but their development and testing requires field data. Data from a long-term USDA-ARS field experiment at Rosemount, MN were used to improve a model, NCSWAP, developed by collaborators at the University of Minnesota. This allowed quantification of the importance of corn roots and root exudates on soil organic carbon and nitrogen. As a result the model will be accurately predict carbon and nitrogen dynamics in corn and corn/soybean systems, making it more useful to scientists exploring the impact of management on soil carbon and nitrogen levels.
Technical Abstract: 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 in SOM. In this publication, results from the same simulations but pertinent to nitrogen 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, Minnesota. 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 15N added with the fertilizer from 1980 until either 1985 or 1992. The same total amount of 15N was added with the 20 and 200 kg N ha-1 fertilizer: 40 and 4 15N atom%, respectively. Corn roots released 24% of total N uptake. This loss was mitigated by the recycling of 14% of rhizodeposition-N into corn by maturity. 15N enrichment in corn and soil was higher for the 20 than the 200 kg N ha-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.