温室分层土壤条件下滴头流量和间距对湿润体的影响

Effect on Soil Wetting Pattern Caused by Emitter Discharge and Spacing for Layered Soil in Sunshine Greenhouse

基于温室田间土壤大多容重分层和不均匀的特点,进行了原状分层、分层筛分均质和筛分均质3种土壤对湿润体影响的对比研究。试验地土壤为粉土(中国制分类),原状分层和分层筛分均质土壤0~20 cm容重为1.44 g/cm3,20~40 cm为1.63 g/cm3,40~60 cm为1.55 g/cm3,筛分均质土壤采用0~60 cm平均容重1.54 g/cm3。滴头流量设2.7 L/h和1.4 L/h二种,滴头间距有30,50,70,100 cm四种,采用剖面法观测土壤含水率和湿润体发展。试验结果表明:①湿润体在现场原状分层土壤、分层均质和均质土壤中有很大的区别,分层筛分均质和筛分均质土壤中均为碗状原状,而分层土壤的湿润体形状在灌水量较小时为碗状,随灌水时间的延长,其形状逐渐变为椭柱体;②土壤容重分层情况对湿润锋的运移影响很大,分层土壤由于20~40 cm容重较大纵向湿润锋发展缓慢,灌水历时8 h时最大纵向湿润锋分别为27 cm和25 cm,且原状分层土壤灌水量较大时出现0 cm深度处横向湿润锋小于-7^-13 cm深度处湿润锋现象;而筛分均质土壤中纵向湿润锋明显大于分层土壤,灌水历时8 h时最大纵向湿润锋为32 cm;③原状分层土壤湿润体内平均含水率高于分层筛分均质和筛分均质土壤,但各组均高于田持,土壤含水率均匀度均在82%以上。基于这种结果,建议设计湿润比应根据温室土壤特点和设计灌水量进行现场测试确定,这样更符合实际情况。

A field experiment about wetting pattern effects caused by original layered, layered homogeneous and homogeneous soil was conducted based on the nonuniformity of the layered soil in greenhouse. The soil in the field belongs to silt loam according to Chinese textural designation. The bulk density of original layered soil and layered homogeneous soil is 1.44, 1.63 and 1.55 g/cm^3 in 0 to 20 cm, 20 to 40 cm and 40 to 60 cm soil depth respectively. The bulk density of homogeneous soil is 1.54 g/cm^3 in 0 to 60 cm. Four emitter spacings of 30, 50, 70 and 100 cm which delivered emitter discharge of 2.7 and 1.4 L/h respectively were applied and section plane was taken to measure wetting pattern and soil moisture in wetted volume. The results showed that the shapes of wetting patterns were deeply different in original layered, layered homogeneous and homogeneous soil. the shapes of wetting patterns in original layered soil were like a bowl at the beginning stage and became an ellipse shape with time. But it was always like a bowl in the other two groups. The difference of bulk density deeply affected the wetted radius and depths. The depths in original layered and layered homogeneous soil developed slowly in the 20 to 40 cm soil depth and the depths under 8 h-irrigation duration is 27 and 23 cm respectively. And the wetted radius at 0 cm depth were less than those in --7 to --13 cm depth in original layered soil when more water were applied. Wetted depth in homogeneous soil was 32 cm and it was the biggest in three soil groups. The average soil moisture in wetted volume were lower in layered homogeneous and homogeneous soil than in＇ original layered soil but all of them were higher than field capacity. The uniformity coefficients of soil moisture in wetted volume for three soil groups were all higher than 82%. These result showed that wetted volume should be tested in the field for drip irrigation design, and this would meet the real instance.