Influence and selection of nitrogen and phosphorus compound fertilizers on emitter clogging using brackish water in drip irrigation systems

Emitter clogging is a major obstacle to the application of brackish water in drip irrigation systems, which can be aggravated with inappropriate fertilizer application. Among the major element fertilizers, nitrogen and phosphorus (NP) trigger a higher risk of clogging. However, the effect and selection of different types of NP compound fertilizers on emitter clogging remain unknown. This study investigated the effects of no fertilizer (CK), two types of industrial grade monoammonium phosphate (I_MAP) and diammonium phosphate (I_DAP), two types of agricultural grade monoammonium phosphate (A_MAP) and diammonium phosphate (A_DAP), and two types of new urea phosphate (UP) and ammonium polyphosphate (APP) on the clogging of three types of emitters. The results showed that the application of agricultural grade A_MAP and A_DAP fertilizers exacerbated emitter clogging compared to industrial grade fertilizers, decreasing the Christiansen of Uniformity (CU) by an average of 18.5%−22.8% and 21.4%−25.6%, respectively, mainly due to an increase in the content of insoluble particulate matter in the clogging material. Application of new UP and APP fertilizers reduced emitter clogging, increasing CU by 29.9%−37.1% and 10.2%−16.4%, respectively, compared to industrial grade fertilizers, mainly by decreasing the chemical precipitate content in the fouling material. Overall, the safe operation time of agricultural grade fertilizer system is about 1.2 years within the safe operation life (CU≥80%) of drip irrigation system, while the safe operation life of industrial grade and new NP compound fertilizers is about 1.6–3.4 times of that of agricultural grade fertilizers on average. It is suggested that in drip irrigation systems using brackish water, A_MAP fertilizer can be applied to annual crops whereas in perennial crops industrial and UP and APP should be applied. This study is of great significance for the application and promotion of brackish water drip fertigation technology.