Effect of Pulsed Irrigation on Crop Water Productivity and Efficiency of Watermelon in Sandy Soil

The use of commonly known irrigation methods (especially surface irrigation or even irrigation under pressure) is limited due to the specific physical characteristics of keeping moisture and lowering the water holding capacity. In sandy beaches or desert plains (called sandstones) with mentioned physical characteristics. lack of nutrients necessary for plant growth restrict the commonly known irrigation application. Gravity Drip Irrigation (GDI) is a new method that avoids the use of extra energy (pumping station). The total amount of pressure head required by the GDI for fields with a maximum area of 100 hectares is between 1 and 3 meters height. The main purpose of GDI is to reduce the required pressure by the drippers. The utilization of drip tape irrigation as one of the GDI methods has been considered in Iran in recent years. Several studies have been carried out in this regard, each of which pursues specific goals. The GDI benefits includes: reducing water consumption per unit area while increasing the moisture content of the plant root zone, increasing water use productivity, the possibility of irrigation in uneven terrain, reducing weed, pests and diseases damage, ease of distribution of fertilizer, requires lower pressure which consequences to lower cost and energy in the production process. Pot irrigation method is one of the most effective methods for irrigating in these conditions with rough terrain, coarse texture and light soils with high water penetration and saline water which surface irrigation methods normally cannot be used. The application of methods that can provide optimal irrigation conditions for such soils with their specific characteristics, such as delay in water infiltration and low outflow, can lead to improved physical conditions and optimal management of these soils. This research was carried out in the first four months of 2016 in a sandy field located in a part of the agricultural land of Jihad-e-Tavan Co. in Kashan city. In this research, according to the custom of the region, the local watermelon of Sunbek district in Aran and Bidgol city, were chosen as a study plant. A factorial design in a completely randomized block including three main treatments of localized irrigation and three irrigation treatments (total of nine treatments) with three replications, as well as furrow irrigation treatment as control were applied. In each row, 12 plants were planted with a distance of one meter on a row and three meters between rows, on an area of 1080 (36×30) square meters. The role of pulsed irrigation cycle in providing favorable growth conditions and consequently increasing yield can be achieved by comparing the performance of localized treatments and control treatment. The Duncan's test results for number of fruits and yield comparison using selected irrigation methods showed that there was no significant difference in the number of watermelons and their weight at the probability level of 1% and 5%. For different irrigation methods, there was a significant difference between yield and number of watermelons at same probability level. By the end of the 110 days after planting, the yield in furrow irrigation, pot irrigation, drip tape and GDI were 11426, 1224, 7527 and 11457 kg/ha, respectively. The improvement percentage of yield in comparison with the control treatment, were 85%, 1034% and 1626% in pot irrigation, drip tape and GDI, respectively. This research results revealed that the ratio of water used to yield in furrow treatments, pot, drip tape and GDI were 1.18, 5.55, 0.9 and 0.09 m3/kg. Also, considering the amount of water used for each treatment, 49.7 and 23.4 percent decrement in applied water in drip tape and GDI and 371.2 percent increment in applied water in pot irrigation observed per kilograms of watermelon produced compared to the conventional irrigation method (furrow irrigation). Highest water productivity index achieved in GDI among the four methods studied, as much as 1.7 kg of watermelon produced per cubic meter of water. In this study, the efficiency of more than 80% achieved in furrow irrigation in sandy soil. Improvement in irrigation efficiency in these soils can be achieved by managing parameters involved like furrow length, time and irrigation discharge. The results showed that with the amount of water consumed equal to 6790 cm3/ha in each of the gravity localized irrigation methods and 13452 cm3/ha in the control treatment, the watermelon yield in pot irrigation, gravity drip, drip tape and furrow irrigation methods were 1224, 11457, 7527 and 11426 kg/ha, respectively, and the water productivity index was equal to 0.2, 1.7, 1.1 and 0.8 kg/ha.m3, respectively. In comparison with the one-day irrigation interval, using pulses irrigation in localized irrigation, irrigation efficiency increased from 87% to 98%. In general, by using localized irrigation in comparison with furrow irrigation in sandy soils, in addition to increasing water productivity, high yield could be achieved in plants like watermelon.