Effect of phosphorus fertigation on clogging in drip emitters applying saline water

Abstract

Abstract. Drip irrigation with saline water has been recognized as one effective method to alleviate the current worldwide water shortage. However, emitter clogging risk could be increased substantially by the complex of ions in saline water. Drip fertigation might aggravate the risk when applying saline water. On-site drip irrigation experiments with a daily operation of 8 h applying saline water were conducted using a plain channel emitter and a labyrinth emitter to investigate the effect of the phosphate fertilizers and the water salinity on emitter clogging. Eight fertigation events were conducted with intervals of 2 operation days. Three typical water-soluble phosphate fertilizer of Monoammonium Phosphate (MAP), Diammonium Phosphate (DAP), and Urea Phosphate (UP) and four levels of water salinity of 0.5 (groundwater, G), 2 (S2), 4 (S4), and 6 (S6) dS m-1 were tested. The treatments without fertigation (NP) for each water salinity level were considered as control. The discharge rates of emitters were measured followed by every 2 fertigation events. Several representative emitters were sampled to measure the dry weight of clogging substances (DW) at the end of the experiments. The plain emitters demonstrated significantly better anti-clogging performance than the labyrinth emitters. For the G treatments, emitter clogging occurred gradually with increasing number of fertigation events. Moreover, the decline rates of the discharge ratio (Dra) were in the order of G-DAP > G-NP > G-MAP > G-UP. The average Dra over the two types of emitters at the end of experiments were 0.56, 0.79, 0.86, and 0.97 for the G-DAP, G-NP, G-MAP, and G-UP treatments, respectively. The better anti-clogging performance of the MAP and UP fertigation could be attributed to the relatively lower pH (6.5 for G-MAP and 2.7 for G-UP, respectively) of the fertilizer solution. Emitter clogging increased greatly with increasing water salinity. For the S2 and S4, the Dra of the treatments with MAP or DAP applied generally decreased to less than 0.6 after 4 fertigation events. However, much slighter emitter clogging was observed for the treatments with UP applied while the average Dra over the two types of emitters at the end of experiments were 0.96, 0.90, and 0.79 for the S2-UP, S4-UP, and S6-UP, respectively. The ANOVA results indicated that the phosphate fertilizer type and water salinity imposed significant effect on the Dra at a significance level of 0.05. In addition, the DW were generally negatively correlated with the Dra for all treatments. Therefore, the strategies for protecting emitter clogging should be developed through comprehensively considering water quality and phosphate fertilizer type used. Using acid phosphate fertilizer is a promising way to alleviate the emitter clogging caused by iron components in saline water.