Field evaluation of fertigation uniformity in drip irrigation system with pressure differential tank

Abstract: Fertigation with drip irrigation systems have become increasingly popular in agricultural and horticultural production. Irrigation and fertilization uniformity are important parameters to quantify and evaluate the quality of water and fertilizer distributions in the fertigation system. To optimize the design and operation of the drip irrigation system with pressure differential tank, the effects of various differential pressures and piping arrangements on the irrigation and fertilization uniformity were comprehensively evaluated through field experiments. The field experiments were carried out at the Water-saving Station of the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas sponsored by Ministry of Education, at the Northwest A&F University. A sampling tap was installed at the outlet of the fertilizer injector to measure the fertilizer solution changes with time. Treatments were 5 differential pressure levels (0.05, 0.10, 0.15, 0.20 and 0.25 MPa) and 4 piping arrangement types (water supply from one end longitudinally, from the middle longitudinally, from one end transversally, and from the middle transversally). Three replications were conducted for each combination. There were 12 sampling points at spacing of 6 m along the longitudinal direction, and 4 sampling points at spacing of 2 m along the transversal direction. The fertigation uniformity was evaluated with 3 indexes, i.e., Christiansen's uniformity coefficient, distribution uniformity and statistical uniformity. The results showed that: 1) the relative fertilizer concentration rapidly decreased in the form of power function, especially in the beginning 15 min under moderate and high differential pressures (0.15, 0.20 and 0.25 MPa) and in the beginning 30 min under low differential pressures (0.05 and 0.10 MPa). At given time, the higher the differential pressure was, the lower the fertilizer concentration was; 2) For water supply from one end and from the middle longitudinally, differential pressure significantly (P<0.05) affected the fertilization uniformity of the fertigation system. However, for water supply from one end and from the middle transversally, the effects of differential pressure on the fertilization uniformity were not significant, when the increase or decrease in pressure differences would not obviously affect the fertilization uniformity and the fertigation time could be adjusted as needed in practice; and 3) For water supply from one end and from the middle longitudinally, the irrigation uniformity under 0.05 and 0.25 MPa was 1.06 and 1.22, 1.06 and 1.14 times higher than the fertilization uniformity, respectively. Overall, the irrigation uniformity of the fertigation system was better than its fertilization uniformity, both of which decreased as the pressure difference increased. Besides, the irrigation and fertilization uniformity of the fertigation system with transversal water supply was better than that with longitudinal water supply, in which the water supply from the middle was further better than that the water supply from one end. To ensure both high irrigation and fertilization uniformity, the piping arrangement with transversal water supply was highly recommended, and the differential pressure of the fertilizer tank should be minimized to extend the fertilization time of the fertigation system. The research provides a scientific guidance for the design optimization and operational management of the drip irrigation system with pressure differential tank in China.