Irrigation schedule for the spring grain corn in Khozestan climate.

One of the most effective factors, which restrict the crop yield, is the environmental stresstimely irrigation can decrease the effects of the environmental stresses. Soil moisture has been considered as a decisive agent for irrigation schedule, while water stress of the crop depends on both factors of soil moisture and climatic conditions. Therefore irrigation schedule should be determined by deficit of soil moisture, air evaporative capacity, plant density and plant sensitivity. The current study intends to investigate the irrigation planning of spring corn (Hybrid S.C.704) in North part of Khouzestan, in 2002 and 2003. this experiment was preformed on the basis of a randomized complete block with five treatments of irrigational interval of 50±5, 70±5, 90±5, 110±5, 130±5, mm on the basis of accumulative evaporation from the evaporation pan with three replications at Safiabad Agricultural Research Center in Dezful. In each irrigation intervalthe volume of water used was calculated on the basis of the soil moisture deficit in the depth of root zone. A day before irrigation, different parameters were calculated such as crop canopy temperature, air temperature, air relative humidity, soil moisture at root zone, sun net radiation, wind velocity, saturated vapor pressure, air vapor pressure and deficit of air vapor pressure with screen box on the experimental field at Safiabad. At harvesting date, five 6-m2 samples were taken from every block treatment. Results of two year study showed that among treatmentscorncob and grain yield were significanly different (at 1% statistical level). The treatments: 50±5 and 70±5 mm in the first year and the treatment 50±5 mm of accumulative evaporation from evaporation pan in 2nd year ranked a level higher than the other treatments. After determining water stress index of plant in each year, correlation test showed that it had a high relation with grain yield especially at the time of flowering. In the end, a multi variation model using the observational date was presented as follows: (Tc-Ta) = 0.1186* RH - 1.633* MD – 0.08008* V +0.0036* Rn –10.941 R2 = 0.811 n=17 In this model parameters are: MD: soil moisture depletion ratio, RH: air relative humidity, Rn: sun net radiation, v: wind velocity and Tc-Ta: air and crop canopy temprature.