Comparative study of ET-based and soil moisture-based irrigation for Al Batinah region in Oman

The agriculture sector in Oman, like in many other countries in the Gulf region, is based on irrigation. While blessed with rich groundwater resources in many parts of the country, Oman's agriculture is plagued with salinity, and most recently sea water intrusion due to excessive pumping in coastal regions, where the main agricultural land is located. In order to address this issue, monitoring and limiting groundwater use for agriculture has been proposed. While a significant amount of extension effort is under way with limited or no success, this paper is an attempt to study how groundwater irrigation could be made more efficient by applying modern technology, especially, sensor-based precision irrigation in Omani agricultural farms. Even though some farms in the Al Batinah region, the largest agricultural area in Oman, have modern irrigation systems installed, hardly any are automated. As such, the operation of various types of irrigation systems are done manually with little or no attention given to water saving. Since the traditional practice of farmers in the country is furrow (flooded) irrigation, the general tendency of them is to apply more water than required to create flooded irrigation conditions. Wherever irrigation controllers are used, the control mechanism has been based on the evapotranspiration (ET) method, which requires the whole water requirement per day to be applied at once and it is inevitable that the soil gets oversaturated causing higher levels of percolation and evaporation loss. In order to prevent this, a soil moisture-based approach is proposed. This paper presents two models developed based on standard relationships for estimating irrigation requirement using both these methods and a comparative analysis showing the application areas where the soil moisture-based method may provide more water saving. It could be seen that the soil moisture-based method saves water at certain soil moisture levels under different field capacities, especially when the ET-based method may incorrectly suggest unnecessarily high water application amounts due to other environmental conditions.