Determining Actual Evapotranspiration of Silage Maize using Soil Water Balance Method under Different Drip Irrigation Levels with Pulsed and Continuous Management (Case Study: Varamin Region)

The proper irrigation scheduling reduces deep percolation losses, saves water and increases crop yield and water productivity. For this purpose, the crop water requirement must be determined carefully. In the present study, the water requirement of silage maize (ZP 606 cultivar) was determined using soil moisture monitoring method in the field conditions. An experiment in the form of split-strip plots based on a randomized complete block design with three replications was conducted in 2019 in Varamin region. The main factor included three levels of irrigation, supplying 120, 100 and 80% of maize water requirement (I2, I1 and I3, respectively) and the sub-main factor included two types of irrigation management: pulsed (P) and continuous (C). The actual evapotranspiration of silage maize under pulsed and continuous management in full irrigation treatment was 364-341 mm, in deficit irrigation treatment was 348-336 mm and in over-irrigation treatment, was 383-352 mm, respectively. The estimated evapotranspiration of silage maize using FAO-56 method was 400 mm that was 13.5% higher than the average actual evapotranspiration for full irrigation treatment in pulsed and continuous management determined by water balance method, which indicated the importance of using local crop coefficient to estimate crop water requirement accurately. The results also showed that the amount of deep percolation in over-irrigation treatment under pulsed irrigation management had decreased by 30% compared to the over-irrigation treatment with continuous management. Therefore, it is suggested to use pulsed irrigation management in order to save water consumption and to reduce deep percolation under drip irrigation system in the study area.