Predicting soil moisture distribution, dry matter, water productivity and potato yield under a modified ‎gated pipe irrigation system: SALTMED model application using field experimental data

The use of gated pipes in surface irrigation helps to reduce water losses commonly associated with the use of the traditional furrows. This study focused on predicting soil moisture content‎, total dry matter, crop yield and water productivity of potato crop using traditional and modified, self-compensating gate outlet (SCGO) gated pipe using the SALTMED model to explore the model suitability to identify the optimum and economic gate spacings. The traditional gated pipes are known to exhibit a range of pressure head variations along the pipeline causing a non-uniform discharge from orifices while the modified gate pipe system, known as compensating gated pipes (SCGO) stabilizes the pressure heads and produce more uniform water discharge along the pipe line. The effect of three gate spacings (0.7, 1.0 and 1.5 m) was studied in a field experiment that has been conducted for two successive seasons, 2011-2012 and 2012-2013. The SALTMED model has been applied and showed excellent agreement between the simulated and observed soil moisture, dry matter, yield and water productivity. Similar to the field results, the simulated values indicated that the modified (SCGO), with the 1.5 m gate spacing, gave the highest yield and water productivity. The modified gated pipe received less water than the traditional gated pipe, due to its high application efficiency. In addition to water saving, there is an economic benefit for using 1.5 m gate spacings as its cost is low (14 gates per 21 m pipe length) in comparison with 1.0 m and 0.7 m spacings. The results confirmed SALTMED ability to simulate with high precision, soil moisture, dry matter, water productivity and yield for potato under gated pipe irrigation. Therefore, the model can be used for design purposes to identify the optimum and economic gate spacings without the need to conduct expensive, costly and labor intensive field trials.