Temperature effect on yield of winter and spring irrigated crops

Extreme weather conditions, such as low and high air temperature changes during the growing season, play a significant role in irrigated crop yield. In this study an iterative chi-square statistical method was used to determine the relationship between air temperature and yield of dominant winter and spring irrigated crops in Shahrekord, Iran. Long term daily weather (1991-2016) and annual crop yield (wheat, barley, potato, alfalfa) data were analyzed and the relationships between low and high crop yield years with maximum and minimum air temperatures was evaluated. Our results indicated that higher temperature during tillering, dormancy breaking and stem elongation (fewer number of days with T-max <= 5 degrees C and greater number of days with Tmax > 20 degrees C) and colder temperature in short time before dormancy breaking led to wheat yield loss. Cold weather during germination, seedling growth and tillering (greater number of days with T-max <= 0 degrees C and excess nights with T-min <= -20 degrees C) as well as cold temperature during breaking dormancy and kernel dough development (fewer days with T-max > 25 degrees C) caused to reduce the barely grain yield. Warmer nights during potato flowering, development of fruit and mid-stage of tuber formation (excess days with T-min > 10 degrees C) and cooler days during potato senescence (greater number of days with T-max <= 20 degrees C) reduced potato tuber yield. Cool weather during emergence of first flower buds and first flowering stages (greater number of days with T-max <= 20 degrees C) led to forage yield loss of alfalfa. Determination of critical periods when these crops are most sensitive to air temperature extremes provides important information for modifying management practices, such as adjusting planting date in order to reduction the negative effects of temperature extremes on crop yield. This information will also be useful for predicting crop yields in different years.