evaluation of a model to simulate wheat growth and development under drought stress conditions

modeling is one of the best tools for quantitative analyzing of biological systems that is helpful for understanding physiological basis of crops growth and development especially under limited water. in this study, a model was developed based on fao penman-monteith model to simulate soil water balance (swb) components and linked with wheat growth and development model, which was developed based on basic models sucros and lintul. a field experiment was conducted in order to presented model validation in 2010-2011 at the ferdowsi university of mashhad research field. experimental design was split plots with 5 irrigation treatments (main plot), 2 cultivars (sub plot), and 3 replications. irrigation treatments included irrigation based on full water requirement (fi), without irrigation during spring (ni), irrigation at the rate of 75% of water requirement (75% fi), irrigation at the rate of 50% of water requirement (50% fi) and irrigation at the rate of 25% of water requirement (25% fi) and subplots also included pishgam (drought-resistant) and gascogne (drought-susceptible) wheat cultivars. then simulated results was validated with two methods: fitted linear regression between observed and simulated data and compare with 1:1 line and root mean square error in percent (rmse %). the result of lai-trend simulation was excellent for susceptible cultivar in non-stress condition (fi treatment) and medium for drastic stress condition (ni and 25%fi treatments). the simulation accuracy was good for other treatments. the lai-trend simulation for resistant variety was good in all treatments. the model accuracy in maximum leaf area index (laimax) simulations and its day ripening was excellent for both varieties. dry matter production of susceptible cultivar was simulated excellent only in fi treatment and good for other treatments. but the model accuracy was gained excellent for resistant variety in all treatments. the model accuracy in yield simulations also was excellent for both varieties. the simulated yield for ni, 25%fi, 50%fi, 75%fi and fi treatments was 1285, 3031, 4697, 6137 and 7649 kg.ha-1, respectively. the actual yield of gascogne variety for the mentioned treatments was 1615, 2954, 4483, 5952 and 8132 kg.ha-1, and for pishgam variety was 1758, 3652, 5071, 6064 and 7548 kg.ha-1, respectively. overall, the results suggesting the effectiveness of presented model to predict wheat growth and development variation under different water supplies but should be revalidated with various experiments to reach better results.