productivity and radiation use efficiency of four dryland wheat cultivars under different levels of nitrogen and chlormequat chloride

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 2006-07 and 2007-08 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 2006-07, the highest biomass production (431.2 g m-2) and rue (0.99 g mj-1 m-2) were obtained from nicknejad cultivar, ccc application, and using 80kgn.ha-1. during 2007-08, the highest biomass production (333.5 g m-2) and rue (0.76 g mj-1 m-2) were obtained from azar-2 cultivar, ccc application, and 80 kg n ha-1. 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.