impact of subsurface water management on drainage water, crop yield, root distribution pattern, evapotranspiration and water use efficiency (case study: maize - karaj)

abstract one of the ways to increase economic and environmental efficiency of drainage systems is water table management. water table management consists of, controlled drainage and subirrigation. this study examines the effect of controlled drainage on yield, root distribution pattern and water use efficiency of maize (sc 704) in karaj. the experiment was performed as a randomized complete design with three replicates including three treatments: free drainage (fd) and controlled drainage with 40 cm (cd40) and 60 cm (cd60) controlled water tables. lysimetric station is equipped with drainage system and water table control system. irrigation intervals in all of the lysimeters were based on mad = 0.65 in fd treatment. for all treatments, irrigation depths were determined based on deficiency of soil moisture from field capacity with 70 percent application efficiency. the results showed that 30 percent irrigation losses during implementation of treatments in cd treatments did not cause rise of the water table to the desired control levels, due to extra consumption of plant. so between two water table control treatments there was no significant difference. in free drainage treatment which drainage water discharge was facilitated lower plant consumption were noted. effect of water table management on yield, irrigation amount, root dry weight and water use efficiency was significant (p<0.01). volume of drainage water in fd treatment was 34.8 percent of total gross irrigation and in cd treatments was zero percent. despite the fact that amount of gross irrigation in fd treatment was more than cd treatments, but useful consumption was higher in cd treatments. dry weight of silage in fd, cd40 and cd60 treatments were 3.94, 6.38 and 6.56 kg/m2, respectively. total root dry weight of fd treatment compared to cd treatments was 43.7 percent more. also water table management led to remarkable changes in root distribution pattern in cd treatments compared to fd treatment. lowest water use efficiency was in fd treatment with 5.32 kg/m3 while in cd40 and cd60 treatments were 9.87 and 10.16 kg/m3, respectively. finally results showed that management strategies of drainage water discharge using controlled drainage, in addition to control of amount of drainage water can be effective on water use efficiency of plants.