Analysis the effect of planting date on wheat genotypes grain yield by using regression methods

The analysis of plant response to environment changes and field managements such as change of planting date based on mathematical patterns is evaluated an effective technique to predict yield. This research was carried out in with 27 genotypes 2010-11 cropping year and with 15 genotypes in three groups late, mid and early maturity in 2012-13 cropping year in Khuzestan Agriculture and Natural Resource Research Center. Each group in each year was investigated as split plots in an independent experiment using complete randomized blocks statistical design with three replications. In each experiment plantings, the date and the wheat genotypes were placed in the main and sub plots, respectively. The Chamran cultivar was considered as the control for all the three groups. In the first and the second year of research, the first planting date for late maturity group were Oct.12 and Oct.27 and for the early maturity group were Dec.11 and Dec.16 and the other two planting dates in each experiment were applied with 10 days interval and for the mid maturity group the first planting date in the first and second year were Nov.11 and Nov.6, respectively and the other two planting dates were applied in the first year with 10 interval and in the second year with 15 days interval. The changes trend of grain yield in each group was investigated in response to planting date change using regression methods and the optimum point of the planting date was calculated based on the maximum grain yield based on differentiable function compared to planting date(dGY/dX). Results showed that in late and mid maturity genotypes, the function of grain yield followed quadratic polynomial trend with strongly R2. In early genotypes, the variations trend of grain functions was a decreased linear trend as a result of delay in planting. As by distance from the first planting date, the grain yield decreased by the amount of 87 kg per hectare in the day.