Irrigation scheduling is determining the appropriate time and quantity of irrigation to reach maximum production. In this research the irrigation scheduling was determined using a computer program CROPWAT , developed by FAO . The program used the climate , crop , and soil data for calculation the irrigation scheduling .The climate data represents average years (1971-2007) of pan evaporation to Mosul city for calculating the reference evapotranspiration , maize crop and light soil data , were used to input data . The program was used cases include three different irrigation timing levels are 100%, 70% and 50% of the readily soil moisture depletion(critical depletion and belowcritical depletion) with refill soil moisture content to field capacity . The results of irrigation scheduling from the program were applied to the field experiment in the Mosul Technical Institute during the summer of 2010. The grain yield and components were measured at harvest to improve the best irrigation scheduling for maize crop in semi arid regions .
The results showed that the depth of irrigation added to three different irrigation levels 100% and 70% and 50% of the readily soil moisture depletion reached 860 and 881 and 900 mmrespectively, the number of irrigations 15, 21, 29 . The results also showed that the best irrigation scheduling for higher water use efficiency was0.55 kg/m3 and highest production356g/m2 for the treatment of 70% of the readily soil moisture depletion. Therefore the CROPWAT is aneffective tool for planning and management of irrigation maize in semi arid regions .