Irrigation scheduling and winter wheat grain yield estimation under precipitation uncertainty - A case study in Badjgah area (Fars Province, Iran)

Addressing deficit irrigation scheduling (DIS) for strategic crop production (especially wheat) under precipitation uncertainty is a priority for irrigation scheduling in drought conditions. This research investigated the precipitation uncertainty by enacting optimistic and pessimistic scenarios for the next 20 years by considering the statistical record of climate in Badjgah area. DIS was conducted in spring in two ways: (1) reducing the quantity of irrigation water at each irrigation event; (2) reducing the number of full irrigation events. Results indicated that, owing to the effect of precipitation increase on yield enhancement, grain yield in the optimistic scenario was on average 7% higher than those obtained in the pessimistic scenario. Furthermore, grain yields obtained via the second method of DIS was on average 8% higher than those obtained by the first method of DIS and further by increasing the water reduction fraction (WRF) to 0.6, this difference reached about 20% due to the effect of early spring irrigation events on yield enhancement. At low irrigation application efficiency (Ea), the difference between DIS methods was greater at higher WRF. Net income obtained through the second method of DIS was on average 70% higher than those obtained via the first method of irrigation for all conditions due to decreasing the number of irrigation events and thus decreasing the production costs. Eventually, results indicated that in both scenarios of the precipitation uncertainty in drought conditions, the second method of DIS, i. e., application of available water based on growth stage, was more fruitful.