Field evaluation of drip irrigation and fertigation performance as affected by lateral layout of subunits

摘要

It has been an accepted practice in China to reduce installation and operational costs by increasing controlled area of an individual drip irrigation system. But the adequate uniformity was always the concern of designers and users. Field evaluationsof system performance were conducted in a drip irrigation system of 153 ha. Three typical subunits with lateral lengths of 96, 64, and 68 m were selected and referred to as Ul, U2, and U3. In Ul and U2, water was fed from both ends of laterals while water was fed from one end of lateral in U3. During the measurement for each subunit, the pressures at the lateral inlet, the middle and the end of each five laterals selected were measured. Besides, water volume and electrical conductivity of fertilizer solution discharged from individual emitters with spacing of 6 m along the five laterals were also determined. The electrical conductivity of fertilizer solution was converted to fertilizer concentration by a pre-calibrated electrical conductivity to solution relation to determine the amount of fertilizer applied by each emitter tested. The evaluation showed that the actual operating pressure for all subunits tested was substantially lower than the target value of 0.1 MPa. The pressures averaged over all the 15 locations measured along the five laterals selected in a subunit were 0.012 MPa, 0.005 MPa, and 0.012 MPa for Ul, U2, and U3, respectively. Similar Christiansen uniformity coefficients (Cu) for the irrigation water were observed for Ul (0.84) and U3 (0.83) although the lateral length in Ul was 1.4 times of that for U3, indicating a better performance offeeding water from both ends of the laterals than feeding water from one end. A relative lower Cu for the irrigation water (0.68) was observed forU2, which could attributed to its extremely lower lateral pressure. A substantially lower Cu for fertilizer applied than irrigation water, roughly lower than 0.55, was found for all the three subunits. Special management practices should be adopted to improve system fertigation performance.