Performance of low-discharge emitters buried in soil as affected by layered-textural soils

Laboratory experiments were conducted using a plexiglass box to investigate the effects of soil layering on discharge performance of a buried emitter. A special SDI emitter with nominal discharge of 1.1 L/h at 10 m pressure was used. Two layered soils, a sandy-over-sandy loam (SL) and a sandy loam-sandy-sandy loam (LSL), and two uniform soils, a sandy loam (L) and a sandy soil (S) were tested. For the SL soil, the thickness of the top layer was 20 cm, and the LSL soil consisted of an upper 20 cm layer of sandy loam soil, a middle 10 cm layer of sandy soil, and a lower 50 cm layer of sandy loam soil (referred to as LSL). The buried depth for emitters for the L, S, SL soils was 15 cm, while three buried depths of 15, 25, and 35 cm were tested for the LSL soil to investigate the effects of the relative positions of emitters to the interface between soil textures on emitter performance. Four inlet pressure heads of 2, 3, 6, and 10 m were tested. The results indicated that the discharge of the buried emitters decreased significantly at the initial period of water application, caused by an increasing back pressure at emitter outlet-soil interface. Then the discharge reached a stable value gradually and the variation of discharge with time could be represented by a power function. Emitter discharge was reduced when the emitter was buried in the soil, especially under low discharge conditions. The sequence and thickness of soil layers had a significant influence on the buried emitter performance. At a given pressure head, a greater discharge was observed for an emitter buried in the uniform soils of L and S than that in the layered soils of SL and LSL. A 20% reduction of emitter discharge from its nominal value was found for the LSL soil as the emitters was buried in the middle layer of sandy soil. A regression equation was established to relate the buried emitter discharge to soil saturated hydraulic conductivity, sequence and thickness of soil layers, and inlet pressure head. The sensitivity analysis demonstrated that the buried emitter discharge was most sensitive to inlet pressure, then to the soil layering, and was insensitive to the soil saturated hydraulic conductivity for the low-discharge emitters tested.