NITROGEN-TILLAGE-RESIDUE MANAGEMENT

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Abstract
Changes in nitrogen, tillage, and residue management influence N dynamics, soil moisture availability, soil temperature, and corn (Zea mays L.) yields. The magnitude of the effect of these parameters on the soil/crop system is determined by initial soil and climatic conditions and can be described by field and simulation experiments. The objectives of this research were to determine the influence of depth to gravel and autoclave-extractable N on corn yields within a nitrogen-tillage-residue field experiment and to compare field data with simulated results. Several techniques were used to evaluate the corn/soil system including: a field experiment consisting of N rates, tillage and residue treatment combinations, spatial variability analysis of pertinent soil parameters, and computer simulation of the corn/soil system. Spatial variability analysis enabled weighting of initial parameter values on an area basis for each of the experimental units within the field experiment. These weighted values were then used to determine the influence of the initial conditions on corn production. This study showed that benefits derived from the corn plant from deeper soil depths depended on the interaction between available water, microbial activity, and the ability of the plant to avoid drought. Corn yields for the simulation system were comparable to observed yields, and the NCSWAP model predicted many of the observed responses.