H. Miranzadeh - Department of Crop Production and Plant Breeding, College of Agriculture, Shiraz University, P. O Box: ۷۱۴۴۱-۶۵۱۸۶, Shiraz, Islamic Republic of Iran.
Y. Emam - Productivity and Radiation Use Efficiency of Four Dryland Wheat Cultivars under Different Levels of Nitrogen and Chlormequat Chloride
H. Seyyed - School of Geography, University of Southampton, Southampton, SO۱۷ ۱BJ, UK.
S. Zare - Department of Water Engineering, College of Agriculture, Shiraz University, Shiraz, Islamic Republic of Iran.

The impact of climate change in the next few decades will increase risks of wheat production under dryland conditions. Therefore, it is important to find cultivars that are tolerant to these conditions and can provide reasonable yield under future climates. Radiation use efficiency (RUE) is the key factor determining the crop yield and is related to crop biomass and leaf area index (LAI). To obtain a high yield from a given cultivar under dryland conditions, it is necessary to achieve optimum RUE. In this study, the effects of different levels of nitrogen fertilizer (N) and plant growth retardant (chlormequat chloride= CCC) on LAI, dry matter accumulation, biomass yield, and RUE of four dryland wheat cultivars were examined. The field experiment was carried out during ۲۰۰۶-۰۷ and ۲۰۰۷-۰۸ growing seasons at the experimental agriculture research station of Shiraz University, Iran. The results suggested that different cultivars varied significantly in LAI, biomass and RUE under similar conditions and demonstrated the dependency of RUE on LAI and biomass yield. During ۲۰۰۶-۰۷, the highest biomass production (۴۳۱.۲ g m-۲) and RUE (۰.۹۹ g MJ-۱ m-۲) were obtained from Nicknejad cultivar, CCC application, and using ۸۰kgN.ha-۱. During ۲۰۰۷-۰۸, the highest biomass production (۳۳۳.۵ g m-۲) and RUE (۰.۷۶ g MJ-۱ m-۲) were obtained from Azar-۲ cultivar, CCC application, and ۸۰ kg N ha-۱. Based on the results of this study, application of N and selecting cultivars resistant to late season drought stress could be considered for improving RUE in dryland farming.

Nitrogen, LAI, Biomass, Chlormequat chloride, Dryland wheat cultivars, RUE