Effect of Dificit Irrigation on Sustainable Utilization of Groundwater Resources

The access to fresh groundwater is playing an imporatant role for sustainable crop production and secure livelihood of people living in the Neyshabour plain. Decline in groundwater table and aquifer fractional are the most important challenges in this plain. In the Neyshabour plain about 84 thousand hectares of agricultural land are cultivated annually and more than 90% of groundwater resources are used in the agricultural sector. In this paper, Soil-Water-Atmosphere-Plant (SWAP) model is calibrated and validated using measured field data from six different fields located in the Neyshabour plain. For this purpose, field information and other SWAP requirement data were collected in the six farm conditions. Calibrated and validated SWAP model is then used to quantify the effects of existing irrigation practices on water balance components and different water productivity indicators for wheat, barley, sugar beet, cotton, silage corn and tomato. Also, the effect of applying the two senarios (1. 20-30% reduction of water consumption during growth period, 2. removal of irrigation intervals in the non-sensitive plant growth stage) was estimated on the reduction of exploiting of groundwater resources. The results showed that under the current irrigation practices, soil evaporation reduced WPET (Yact/ETact) over WPT (Yact/Tact) by 24%, 26%, 27%, 21%, 8% and 15% for wheat, barley, sugar beet, cotton, silage corn and tomato, respectively. The reduction in WPETQ (Yact/ETact+qbot) over WPET because of deep percolation was even higher and remains 50%, 44%, 33%, 37%, 14% and 53% for wheat, barley, sugar beet, cotton, silage corn and tomato, respectively. The substantial differences in WP values emphasized the need to control non-beneficial soil evaporation and deep percolation losses, and change traditional irrigation system by a more efficient one. Applying deficit irrigation management for the six major crops in the neyshabour plain resulted in a 27% reduction in the extracting of groundwater aquifer with a change in yield +4 to -17%. This less withdrawal amount is equal 105 million cubic meters of exploiting of groundwater and compensates for 77% of the reservoir fraction in the Neyshabour plain. Removing an irrigation turn for six malor crops in the Neyshabour plain causes a 17.5% reduction in exploiting from groundwater aquifer with a decrease in yield from 4 to 10 percent. This amount of discharge is equivalent to saving 69 million cubic meters of groundwater, thus compensating about 50% of the groundwater aquifer fraction.