Effects of fertilizer type and concentration on the clogging characteristics of emitters and anti-clogging strategies

Water-saving irrigation area has increased steadily in China, with the rapid development of mechanized farming and land transfer. Among them, drip irrigation can greatly contribute to agricultural water-saving and high efficiency in northwest and northeast China. Drip irrigation can directly transport the fertilizer with water to the root zone of crops, and then effectively improve the fertilizer utilization rate. But the improper fertilization can lead to emitter blockage and a decrease in fertilization uniformity, resulting in crop yield loss. It is a high demand to implement chemical blockage in the field, due to the high requirements. In this study, the clogging performance was tested using commonly-used emitters (Inlaid cylindrical labyrinth emitter, E1; Inlaid patch labyrinth emitter, E2; Flanking labyrinth emitter, E3) with the Urea (UREA), Sulphate of potassium (SOP), Muriate of potash (MOP), Monoammonium phosphate (MAP), Diammonium phosphate (DAP) under different concentrations (0, 0.4, 0.8, 1.0, 1.2 g/L). The morphology and composition of clogged substances inside the emitter were analyzed to combine with field emission scanning electron microscopy (FESEM), surface energy spectrum analysis (EDS), and X-ray diffractometer (XRD). The sensitive fertilizer and emitter were then determined for the reasonable suggestions of fertigation. A theoretical basis was provided to inhibit the chemical clogging by an indoor simulated irrigation acceleration experiment. The results showed that there were different effects of fertilizers on the hydraulic properties and clog development of drip irrigation tape. There was no influence of potassium fertilizer on the hydraulic properties of E1 and E2, but little effect was found on the clogging degree of E3. Little influence was found in the mono-ammonium phosphate on the hydraulic performance of E1, but there was a slight blockage to E2 and E3. Diammonium phosphate was irrelated to the hydraulic performance of E1, but there was a slight blockage to E3, and a serious blockage to E2. Urea did not affect E1 and E2, but there was a clogging risk to E3. Therefore, the UREA and DAP were recommended to be avoided in irrigation. The uniformity increased with the increase of urea concentration in the range of 0.4-0.8 g/L, while the uniformity decreased in the range of 1.0-1.2 g/L. By contrast, the relative average discharge and irrigation uniformity of E3 decreased with the increase of irrigation times, whereas, the decrease rate increased with the increase of fertilizer concentration, as the diammonium phosphate concentration increased. Thus, the fertilization concentration of diammonium phosphate should not exceed 1.2 g/L. The local bulges on the surface of clogged substances were gradually higher than the initial state in the process of irrigation. The attached fouling was thinner, whereas, there was an increase in the scaly structures and the surface roughness. After irrigation, the attached fouling layer thickened, the surface roughness developed completely, and the structure was encrypted gradually from wide-scale structure to fine-scale structure. The dry weight of the clogged substance increased with the increase in the irrigation time. There was the consistency with the trend that the relative average discharge and uniformity of the emitter decreased with the increase in irrigation times. The more chemical fouling increased, the less the effect of water shear force on it, as the concentration of fertilizer solution increased. It is necessary to further improve the filtration efficiency of irrigation water, and reduce the content of suspended solids in irrigation water. A reasonable and perfect evaluation of water quality can also be conducted to reduce the occurrence of chemical blockage in fertigation systems.