Geographical Research

Crop development is qualitative changes planned that led the plant to ripening. Under irrigated conditions expected only climate elements able to change of plant growth and development and under these conditions, temperature and day length have more effective than the other elements. Data from planting dates trials conducted over the Kabootar-Abad Agricultural Research Station during 2003-2009 were used to develop models for estimating development rate of three varieties, Arak, Zendehrud and Goldasht. To calculate of developmental rate of every stage, duration of every stage was nversed. For determining model of development rate of every stage, development rate considered as dependent variable and day length, thermal ariables and combination of these considered as independent variables in step wise regression. A step of regression was considered appropriate if the highest R2 was accompanied by the significant (p≤0.05) regression coefficient. Evaluation of model accuracy and sensitivity was performed, using the data of 2008-2009 that there was not any role in forming of models. No. of days from planting to emergence, emergence to heading, emergence to flowering, emergence to ripening and flowering to ripening were affected by planting dates. By increasing temperature, developmental stage periods decreased. Day length had the most effect on emergence to heading and emergence to flowering period and by increasing it, decreased. Tmean was the only variable that entered to model and explained about 76% of development rate of emergence period. About 83% of development rate of emergence to heading stage was determined by Tmax×DL. T2 max×DL2 explained about 92% of development rate of emergence to flowering stage. T2 max×DL2 with T4 max xplained about 81% variations of developmental rate of emergence to ripening stage.T3max was the only variable that entered the model of development rate of flowering to ripening stage and expressed about 47% variations of it. Contribution of thermal and day length parameters in determining of rate of different developmental stages is not constant. This may be related to different physiological nature of developmental stages and differences reactions of these stages to climatologic, edaphic and agronomic elements and interaction among them and with genotype of plant. Contribution of thermal and day length parameters in determining of rate of different developmental stages is not constant