Effect of drip irrigation frequency on emitter clogging using reclaimed water

Drip irrigation frequency has important impacts on crop growth, soil moisture, nutrient, salinity and substances’ accumulation in the irrigation system as well as drip irrigation emitter clogging. However, previous studies on reasonable drip irrigation frequency merely focused on crop yield and quality, soil water and salinity transporting, neglecting its impact on the high-efficiency operation of the drip irrigation system. Studies on reasonable reclaimed water drip irrigation frequency were more insufficient. Therefore, the drip irrigation emitter clogging experiment using reclaimed water was accomplished in the wastewater treatment plant, and then, the effects of different irrigation frequencies, including once/2 days (IF1/2), once/4 days (IF1/4), once/8 days (IF1/8) and once/16 days (IF1/16), on dynamic emitters’ outflows and biofilms’ growth were studied. The results showed that emitter clogging degrees increased with shorter drip irrigation interval, mainly because that discharge ratio variation (Dra) and Christiansen uniformity coefficient (CU) both decreased. After the system accumulatively run 540 h, the smallest Dra and CU were observed in high-frequency drip irrigation treatment (IF1/2) as 30.98 and 31.97 %, respectively, along with the highest proportion of more serious clogged emitters, due to the effects of drip irrigation frequencies on the comprehensive biofilm growth and detachment inside emitters. The dry weights (DWs), extracellular polymeric substances (EPS) and phospholipid fatty acids (PLFAs) of biofilms all increased with shorter irrigation interval, and showed logarithmic relationships (R2 > 0.92). The max DW, EPS and PLFAs of biofilms in IF1/2 reached 0.124 g, 1459.80 and 96.07 μg, respectively, after 540 h. Combined these with previous studying results, irrigated between once/8 days and once/4 days was believed to be appropriate for planting maize in North China Plain using reclaimed water drip irrigation.