Determination of first lateral flushing time and period to mitigate risk of emitter clogging in drip irrigation

Flushing the drip tubes (laterals) is one of the simplest, most convenient and effective methods for anti-clogging of emitters. However, it is still unclear whether the lateral flushing lowers the risk of emitter clogging in the drip irrigation system watered by Yellow River. In order to explore the influence of lateral flushing periods on the risk of emitter clogging during the integrated irrigation process of water and fertilizer in Yellow River drip irrigation area, a set of short-cycle indoor drip irrigation simulation tests were carried out under 4 different flushing periods (3, 5, 7 and 10 d) and 2 kinds of water (0.8 g/L sediment concentration without urea and 0.8 g/L sediment concentration with 1% urea) in the study. The mean relative flow rate, the recovery rate of flow after flushing events, the flushing rate of sediment in laterals and the particle composition of the sediment were analyzed. The results showed that after the irrigation of muddy water, the mean relative flow rate in flushing treatments were 14.29%-47.77% higher (P<0.05) than that under the no flushing (CK) treatment, while after the drip irrigation of muddy water drip irrigation with urea, the mean relative flow rate in the flushing treatments were 12.89%-126.67% higher (P<0.05) than CK. It indicated that laterals flushing reduced the risk of emitter clogging in Zhongwei Yellow River drip irrigation area. According to the ability to maintain the flow rate after laterals flushing, the whole operation period of drip irrigation was classified into 3 stages: insensitive, sensitive and ineffective flushing period. And the first flushing event should be performed before the end of the insensitive flushing period. Analysis of variance results showed that the effect of applying urea and flushing period on the relative flow of emitters was extremely significant either in a separate way or in an interactive way, which indicated that within a certain concentration range of sediment, the application of urea would affect the risk of emitter clogging, and the flushing periods had a great influence on the relative flow of emitters. The treatment group with the flushing period of 5 d had the highest rate of recovery flow, and the recovery flow rate of the other flushing periods were about 0.36%/time to 0.41%/time. Under the 2 kinds of water drip irrigation conditions, the flushing rate of sediment under different flushing periods showed a decreasing trend with increasing flushing periods, indicating that the accumulation of sediment mainly occurred in the initial stage of irrigation. The variance analysis of the particle size composition of sediment showed that flushing period had a great influence on the sediment, and the effects of different flushing periods on the composition of sediment were different. Fine sediment was easy to settle in the laterals during the irrigation process. And the application of urea increased fine particles settled in the laterals. In Yellow River drip irrigation area of Zhongwei, Ningxia, lateral flushing could reduce the amount of sediment deposited in the capillary, restore the cross-sectional areas of the emitter, and maintain emitters flow at a high level for a long time. The first flushing should be taken before the end of insensitive flushing period. When drip irrigation system reached the ineffective flushing period, the laterals need to be replaced or the other anti-blocking measures should be taken. During the dripping process of the Yellow River in Zhongwei, Ningxia, the first flushing measure should be carried out after the first 2 times of irrigation for muddy water drip irrigation system, and 9 times of irrigation for muddy water drip irrigation system with urea. In addition, suitable flushing periods were 5 and 7 d for muddy water drip irrigation system and muddy water drip irrigation system with urea, respectively. The proposed suitable lateral flushing period for drip irrigation is expected to improve the adaptability of drip irrigation technology in the Zhongwei, Ningxia Yellow River drip irrigation area.