EFFECT OF NITROGEN SUPPLY ON MAIZE YIELD .1. MODELING PHYSIOLOGICAL-RESPONSES

Much of the increase in maize (Zea mays L,) yields in recent decades h as been closely associated with increased levels of N fertilizer appli cation. Although many studies have documented yield responses to incre ased N levels in the soil, a mechanistic description of the physiologi cal responses that influence crop growth under various levels of N has not been fully elucidated. The objective of this work was to develop a relatively simple, mechanistic model of maize growth and development to account for the influence of soil and crop N budgets,The soil N bu dget was simulated for two soil layers that incorporated fertilization , mineralization, denitrification, and leaching, Crop uptake rate of N was simulated by a supply function that depends on cumulative and dai ly thermal units, soil water content, and soil N availability, Compari son of simulated and experimental crop N uptake through the season sho wed especially good agreement for 0 to 12 g N m(-2) fertilizer treatme nts, At 24 and 42 g N m(-2), the simulated crop N uptake was greater t han observed, Nevertheless, comparable seasonal patterns between simul ations and observations at all fertility levels were obtained for accu mulated total biomass and grain. Final grain yields for all fertility treatments were simulated to be within 8% of the observed. A sensitivi ty test was performed with the model to investigate the importance of various physiological parameters on biomass accumulation and yield, Yi eld estimates under low soil N levels tended to be most sensitive to m inimum grain N concentration.