Effects of phosphorus-fertigation on emitter clogging in drip irrigation system with saline water

Abstract Phosphorus (P) is an essential element for crop production. Drip irrigation (DI) system, mainly because of its high precision, allows effective application of water-soluble P-fertilizers. However, consecutive input of P-fertilizer would react with ions in the water source, especially when using the saline water containing high concentration of ions. Consequently, the integration of P fertilizer and saline water results in more complicated and serious DI emitter clogging, which may damage the whole irrigation system. Therefore, an in-situ field study was conducted to study the impacts of saline water concentrations (2 g L−1 and 4 g L-1) and water-soluble P-fertilizer types (urea phosphate, UP; and mono-potassium phosphate, MKP) on DI system performance. The results indicated that both UP and MKP application aggravated the emitter clogging process, and decreased the system discharge variation ratio (Dra) and Christiansen coefficient of uniformity (CU) by 2.62 %–11.7 % and 1.89 %–7.94 %, respectively. UP treatments performed better than MKP treatments in anti-clogging abilities, as it increased the DI system Dra (4.81 %–5.78 %) and CU (2.98 %–3.59 %). Besides, the impacts were significantly enhanced by higher water salinity. The system performance indicators were closely related to the chemical precipitations inside emitters, especially the relative contents and variations of the primary components (carbonates, quartz and silicates). UP performed better than MKP mainly because it lowered water pH and thus significantly reduced precipitation. Overall, clogging parameters (Dra and CU), clogging substances and the components of fertigation treatments all showed positive linear correlations with controlled treatments that without fertilizer applied (CK_2 and CK_4). The slopes of the fitting curves and significance analysis results combined demonstrated that, the water salinity had larger impact on emitter clogging process than fertilizer types. Present study offered references to fertilizer application using saline water to maintain drip irrigation system’s benefits.