Critical Threshold Temperatures and Rainfall in Declining Grain Yield of Durum Wheat (Triticum Durum Desf.) During Crop Development Stages

The effects of maximum temperature, rainfall and growing degree day on grain yield of durum wheat (Triticum durum Desf.) were studied during the period of available years (2005-2017) in the study sites. A polynomial equation was described the relationship between grain yield, maximum temperature and rainfall for four growing stages of winter wheat. The nonlinear relationships were used from time-series variations in temperatures, rainfall and yields. The maximum positive effects of rainfall (R2=0.72*) on grain yield was in the mid-season stage (heading, anthesis and grain filling) of the crop. However, there was a negative effect of temperature more than 30°C on grain yield. The highest negative effects (R2=0.31 through 0.86*) of maximum temperatures were in the crop development stages (vernalization and tillering). The yield might decrease about 2.5% for every 1°C increase in the growth period based on the daily mean temperature of 12.4°C for all the study locations. The critical maximum temperatures on threshold values declining yield and positive effects of rainfall on grain yield varied according to the altitudes and longitudes.