土壤层状质地对小流量地下滴灌灌水器特性的影响

以均质壤土（L）、均质砂土（S）、上砂下壤（SL）和壤土中有砂土夹层（LSL）4种土壤质地结构为对象，利用室内土箱试验，研究了土壤质地及其层状结构对灌水器流量的影响，估算了灌水器出口正压值。试验选用10 m水头压力下额定流量为1.1 L/h的地下滴灌专用灌水器。土壤为层状结构时，上层土壤厚度为20 cm，砂土夹层的厚度为10 cm。L、S、SL试验的灌水器埋深为15 cm；为了探讨灌水器埋深与土壤质地变化相对位置对灌水器性能的影响，LSL的灌水器埋深设计为15、25和35 cm。试验采用的工作压力为2、3、6和10 m水头。结果表明：灌水开始后，出口正压的迅速增大致使灌水器流量迅速减少，而后逐渐趋于稳定。灌水器流量随时间的变化可近似用幂函数表示。灌水器在土壤中的流量比在空气中的自由出流流量有所减小，灌水器自由出流流量越小，减小幅度越大。土壤层状质地对灌水器流量影响明显，一定压力下，灌水器在层状土壤中的流量小于在均质土壤中的流量，尤其当灌水器位于LSL的砂土夹层中时，流量比在均质壤土中减少13%，比自由出流流量减少20%。利用试验结果建立了地下滴灌灌水器流量与土壤饱和导水率、层状土壤结构、灌水器工作压力的经验关系，对各影响因子的敏感性分析结果表明，对地下滴灌灌水器流量影响最明显的是灌水器工作压力，其次是层状土壤结构，饱和导水率的影响较小。

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.