Nitrogen Argument for Corn Leaf Area Models
When soil N fertility is low, it should be considered in predicting corn (Zea mays L.) leaf area index (LAI). Measurements of LAI in 1978, 1979, 1983, and 1984 were used to develop an N growth factor (NGF) to reduce daily LAI increase before silking, based on N fertilizer rate (NR) and LAI in a corn LAI model developed for non-N limiting conditions. With the NGF there is no reduction in rate of LAI increase when LAI is below a critical value (LAICNR) determined by NR. After LAI exceeds LAICNR, NGF reduces the rate of LAI increase according to NR. After silking there was no apparent N effect on the rate of LAI decline. A LAI prediction model using NGF was tested against independent LAI measurements in 1985, including data from plots receiving no N fertilizers. The LAI prediction errors were less than 20% for most of the season. This empirical NGF is a method to lower LAI predictions for corn with low N applications in models in which N fertility has not been considered.
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