Abstract
Maize yield is mainly controlled by nitrogen (N) fertilizers. Failure to predict economic optimum N rate causes over-fertilization of N through traditional application methods. Five field trials were conducted to study soil-crop N relationships in maize under field conditions. Optimum level of N application in this study was much lower than conventional N fertilization in calcareous soils of southern Iran, demonstrating over-fertilization of N fertilizers by farmers. Linear regression equations were found between total nitrogen (TN) and chlorophyll meter readings (CMR) (years 2001 and 2002) in both locations demonstrating that chlorophyll meter might be used in predicting TN in maize shoot. Results indicated that soil sampling location influenced on soil NO3-N concentration at 4–6 leaf stage. In conclusion, N use efficiency can be improved by in-season soil NO3-N testing. It appears that in Kooshkak and Bajgah experimental stations, soil samples for NO3-N testing should be collected from shoulder and bottom of furrows, respectively.
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