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| DOI：10.13522/j.cnki.ggps.2019316 |
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| Effect of Phosphorus and Nitrogen Fertigation on Clogging in Drip Emitters Applying Saline Water |
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YANG Xiaoqi, WANG Zhen, LIU Hongquan, LI Jiusheng
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1. Institute of Urban and Rural Construction, Agricultural University of Hebei, Baoding 071001, China; 2. State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin,
China Institute of Water Resources and Hydropower Research, Beijing 100048, China
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| Abstract: |
| 【Objective】Drip irrigation has been regarded as one of the most effective ways to apply saline water to crops as the water could be irrigated at a high frequency and low discharge rate, resulting in relatively low salinity levels in the soil due to leaching. However, the diverse ionic composition (Na+, Ca2+, Mg2+, HCO3-, SO42-, etc.) in saline water may accelerate the formation of clogging sediments, thus obstructing the emitters, has been considered as a major problem in drip irrigation systems. Besides, emitter clogging risk might be increased by the fertigation practice for the drip irrigation system applying saline water. The objective of this paper was to evaluate the clogging process and mechanisms in drip emitters during the application of saline water with combined P and N fertigation. 【Method】On-site drip irrigation experiments applying saline water were conducted using a plain channel emitter (E1) and a labyrinth emitter (E2) to investigate the effect of the phosphorus and nitrogen fertigation and the water salinity on emitter clogging. In the test, four combined phosphorus and nitrogen fertigation practice were produced by integrating one typical phosphorus fertilizer (Monoammonium Phosphate (MAP) or Diammonium phosphate (DAP) ) with one typical nitrogen fertilizer (Urea (U) or Ammonium Sulphate (AS)). Besides, three saline water qualities with electricity conductivity of 2 (S2), 4 (S4), and 6 (S6) dS/m, respectively, were tested with the groundwater (G) that was considered as the control. The discharge rates of emitters were measured followed by each fertigation event. Several representative emitters were sampled to measure the dry weight (DW) and the chemical constituents of the clogging substances in the emitters at the end of the experiments. 【Result】 The mean discharge ratio (Dra) averaged over the E1 treatments with an operation of 96 h was 19% higher than that for the E2 treatments. The plain emitters demonstrated significantly better anti-clogging performance than the labyrinth emitters. Under groundwater irrigation, a relatively slighter decrease of Dra with time was observed for the G treatments while emitter clogging increased obviously with water electricity conductivity. A greater DW represents more severe clogging in emitters while a significantly negative correlation was found between the DW and the Dra. Phosphorus and nitrogen fertigation produced rapid clogging of emitters in the drip irrigation system applying saline water with electricity conductivity larger than 4 dS/m. Phosphate sediments account for more than 85% of DW for the S4 and S6 treatments. The emitter clogging occurred more easily for treatments with DAP fertigated than those for the treatments with MAP fertigated. The averaged DW of the clogging substances over the treatments with MAP applied were 76% and 41% lower than those for the treatments with DAP applied under groundwater and saline water (S2) application, respectively. 【Conclusion】The phosphorus-coupled nitrogen drip fertigation should be applied with cautious applying saline water with electrical conductivity higher than 4 dS/m. Using acid phosphate and nitrogen mixture fertilizer is a promising way to alleviate the emitter clogging caused by iron components in saline water. |
| Key words: drip irrigation; emitter; fertigation; saline water |
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