Determining injection strategies of phosphorus‐coupled nitrogen fertigation based on clogging control of drip emitters with saline water application*

Abstract The beneficial effect of fertigation with acidic fertilizers to protect emitters from chemical and biological clogging might be inhibited by improper fertigation modes. An on‐site drip irrigation experiment was conducted to investigate the injection strategies of phosphorus (P)‐coupled nitrogen (N) fertigation and water salinity on clogging of emitters with plain channel and labyrinth structures. The results demonstrated that the H+ in acidic P fertilizer solutions inhibited the precipitation of carbonate and phosphate simultaneously. However, a weak acidic P fertilizer could no longer protect the emitters from clogging effectively under saline water with an electrical conductivity (EC) exceeding 2 dS m−1 because the phosphate sediments accounted for more than 80% of the total clogging substances. A strategy of applying a weak acidic phosphate fertilizer following N fertigation performs better in reducing emitter clogging than fertigation using N and phosphate fertilizers together. The target pH values were obtained as 6.0, 4.0, and 3.0 for protecting emitters from clogging for drip irrigation systems applying irrigation water with an EC of 0.5, 2.0, and 4.0 dS m−1, respectively. An optimal fertigation mode for emitter clogging control should consider water quality, type and pH value of fertilizer, and emitter type comprehensively.