effect of drip tape placement depth and values of applied water on yield and water productivity of potato in dehgolan plain

introduction: water scarcity is one of the primary problems in arid and semi-arid regions such as iran. in these regions, increasing water productivity in agriculture sector is inevitable. water productivity can be increased using the drip irrigation method and application of irrigation strategies such as deficit irrigation. potato is the major crop in dehgolan plain. researches have shown that the potato crops very sensitive to water stress. sprinkler and furrow irrigation systems are common methods for irrigation of potato crop in dehgolan plain. in this plain, the main supply for irrigation water is groundwater resources. due to the falling water table in this plain, high sensitivity of the potato crop to water stress and low efficiency of current irrigation systems in the plain, the use of modern methods such as drip-tape irrigation system is inevitable. drip tape irrigation is one of the efficient methods to increase water productivity of agricultural crops. in this method, determining the optimal drip tape placement in the soil and irrigation water depth are the important factors for obtaining maximum yield and irrigation water productivity of potato crop. the purpose of this study was to investigate the effect of drip tape placement depth and irrigation level on water productivity of the potato crop (agria cultivar) in dehgolan plain of kurdistan province. materials and methods: a field experiment was conducted to evaluate the effect of drip tape placement depth and irrigation water level on water productivity of the potato crop (agria cultivar) in dehgolan plain of kurdistan province in spring season of 2014. the results of water quality analysis showed that the irrigation water has not any limitation to plant growth. the soil texture of the field was silty clay. the experiment was arranged in split plot design based on randomized complete blocks design with three replications. the main plots and subplots included the irrigation water levels (60, 80, 100 and 120 percent of the potato water requirement) and drip tape placement depth (0, 5, 10 and 15 centimeters), respectively. at the end of the growing season, tuber yield of potato was measured. measured data were analyzed using statistical software, r.also, mean comparisons were done using duncan's test. results discussion: the results showed that the effect of irrigation water and drip tape placement on yield and water productivity was significant (p= 0.01%). the maximum yield and water productivity of this crop were related to 120 and 60 percent of crop water requirement, respectively. the results also showed that drip tape placement depth equal 15 cm was the depth when using drip tape irrigation system in dehgolan plain. economic analysis of different treatments showed that irrigation water depth equal 120 percent of the potato water requirement has higher benefit–cost ratio than other treatments, but the water produced related to it is minimized. since the dehgolan plain faced with an intense water deficit and groundwater level of this plain has lost, so maximizing the amount of water produced in dehgolan plain is inevitable. the results showed that the applied irrigation water depth equal 60 percent of potato water requirement and installation of irrigation tape at a depth of 15 cm can be achieved highest irrigation water use efficiency of potato in dehgolan plain. the result of this research indicated that tuber yield and water productivity of the potato crop under subsurface drip irrigation systems is higher than surface drip irrigation. the ability of subsurface drip irrigation in the improving of tuber yield could be attributed to the less water lost from the soil surface through evaporation. subsurface drip irrigation allows maintenance of optimum soil moisture content in the root zone, which improved the water productivity. conclusion: the results show that the maximum tuber yield of potato was related to 120 percent of the potato water requirement. but the maximum irrigation water use efficiency was related to treatment water equal 60 percent of water requirement and drips tape placement depth equal 15 cm. as a result, recommended to increase the irrigation water use efficiency in dehgolan plain, deficit irrigation strategies applied. the results also showed that the yield and water productivity of the potato crop in subsurface drip irrigation method is more than surface drip irrigation method. in this way the growth of weed and water loss through evaporation was very low and therefore the plant uses the greater amount of irrigation water.