Interaction and adaptation of phosphorus fertilizer and calcium ion in drip irrigation systems: the perspective of emitter clogging

Emitter clogging is a major challenge for phosphorus drip irrigation systems (PDIS). Calcium ions (Ca2+) play an important role in PDIS clogging. However, the effects of Ca2+ and phosphorus fertilizer interactions on emitter clogging are largely unknown. This study investigated the emitter clogging behaviors with four Ca2+ concentrations (25, 50, 100, and 200 mg L−1) and three phosphorus application strategies (no-fertilization, urea phosphate, and mono-ammonium phosphate). Results show that Ca2+ concentrations, phosphorous fertilizer, and their interaction significantly affected emitter clogging. At low concentrations of Ca2+, phosphorus fertilizer applications reduced emitter clogging when compared to no-fertilization. When Ca2+ concentration was 25 mg L−1, phosphate fertilizer reduced the dry weight of clogging substances by 25–45%. Because the phosphate ions (PO43-) hydrolyzed from phosphate fertilizer competed for Ca2+ with carbonate ions (CO32-), which reduced the formation of calcium carbonates. In contrast, phosphorus fertilizer applications increased emitter clogging at high Ca2+ concentrations. When Ca2+ concentration was 200 mg L−1, phosphate fertilizer increased the dry weight of clogging substances by 18–36%. Because abundant Ca2+ interacted with PO43- to form phosphate precipitations. Furthermore, urea phosphate posed fewer clogging risks than mono-ammonium phosphate, and the demarcation Ca2+ concentrations (i.e., no increase or decrease in emitter clogging after fertigation) for urea phosphate and mono-ammonium phosphate were approximately 150 mg L−1 and 50 mg L−1, respectively. Lastly, phosphate fertilizer application and a rise in Ca2+ concentration significantly increased the deposition of water particles. To mitigate emitter clogging of PDIS, it is suggested that phosphorus fertilizer types and suitable Ca2+ concentrations be adapted, as well as water filtration should be enhanced. This study clarified the effects of phosphate fertilizer and Ca2+ coupling on emitter clogging, with implications for resolving the PDIS clogging issue and promoting the application of phosphorus drip irrigation technology.