Yield Reaction to Evapotranspiration of Maize, Under the Effect of Water Stress at Different Growth Stages (In Qazvin Plain)

In this research, the yield and evapotranspiration of maize were investigated under water stress at different growth stages. The experiment was performed as factorial in a randomized complete block design. Treatments included m water stress at growth stages of 4-leaf, 12-leaf, flowering, grains doughing and a control treatment under full irrigation. Daily plant evapotranspiration was measured based on soil water balance in the root zone. The total amounts of evapotranspiration in the control and the proposed treatments (water stress at growth stages of 4-leaf, 12-leaf, flowering, grains doughing) were estimated to be 462, 401, 322.5, 304.5 and 355 mm, respectively. Similarly, the dry biomass of maize was equal to 15025, 14422, 11384, 7746 and 13416 (kg. ha-1), respectively. Descending amounts of evapotranspiration and yield were correspond to control, 4-leaf, doughing, 12-leaf and flowering treatments, respectively. The reason was the sensitivity and different need of plant to transpiration, at different growth stages. To evaluate the yield response to maize evapotranspiration, the value of  coefficient in the mentioned growth stages was determined to be 0.3, 0.8, 1.42 and 0.46, respectively. At the flowering stage, the value of  coefficient was higher than one, which indicates that the yield of maize is reduced more than the evapotranspiration. The amount of water productivity in the control and stress treatments were calculated to be 3.25, 3.6, 3.53, 2.54 and 3.78 (kg.m-3), respectively. The highest to lowest values were corresponded to seeds doughing, 4-leaf, 12-leaf, control and flowering treatments, respectively. The results showed that the full irrigated plant (control treatment) was not a guarantee to increase the water productivity. Rather, by refusing to achieve the maximum yield and accepting the low reduction in yield, water productivity can be increased. Under these conditions, selecting the suitable plant growth stage for low irrigation was also important.