EFFECT OF NITROGEN SUPPLY ON MAIZE YIELD .2. FIELD AND MODEL ANALYSIS

Experiments investigating the yield response of maize (Zea mays L,) to applications of fertilizer N are generally analyzed empirically. Whil e the nature of the yield response can be characterized, information o n the effects of various components influencing the soil and crop N bu dgets are unresolved, The objective of this study was to examine the r esults of a series of N fertility experiments with the aid of a mechan istically based crop model. The experiments resulted in grain yields r anging from 99 to 1102 g m(-2), and these yields were well simulated b y the model (r(2) = 0.97). Under high fertility conditions, temperatur e and solar radiation interception explained the variation in yield am ong environments. Under low fertility conditions, mineralization of so il organic N was especially important in explaining yield variations a mong environments, Management practices preceding the experimental cro ps were hypothesized to have large effects on the N availability in th e soil, and consequently influence observed and simulated yields, Sens itivity tests confirmed the importance of defining the initial soil or ganic N levels in simulating crop growth and yield when there is littl e or no applied N fertilizer.