A MODEL TO ASSESS NITROGEN LIMITATIONS ON THE GROWTH AND YIELD OF SPRING WHEAT

Under many conditions the availability of soil nitrogen imposes an important constraint on wheat (Triticum aestivum L.) yields. In this paper a simple, mechanistic model of spring-wheat growth and yield was proposed to account for nitrogen uptake and use by the crop. A soil nitrogen balance was developed so that crop nitrogen uptake was restrained when the available mineral nitrogen in the soil was exhausted. The crop nitrogen uptake rate was calculated as a function of cumulative thermal units. Leaf area development and maintenance, radiation-use efficiency, and stem growth were assumed to depend on accumulated nitrogen. Seed growth resulted in nitrogen transfer from leaves and stems to the seeds. The model was compared against data collected in nine years of experimentation at Gilat, Israel. Good agreement between observed and simulated yields was obtained for varying nitrogen fertilizer treatments (r2=0.94) and levels of soil nitrogen following fallow (r2=0.93).