坡度对3种单环法测量坡地饱和导水率的影响

摘要

为探寻坡地土壤饱和导水率(Ks)的田间测量方法,利用基于水平地面发展而来的单环双水头法、单环单水头法和单环BEST法测量3种类型土壤(风沙土、黄绵土和塿土)的Ks,分析坡度(0°、5°、10°、15°、20°)对3种测量方法所测定Ks值的影响.结果表明:3种方法测定的不同类型土壤Ks大小顺序一致,但是单环BEST法显著高于单环双水头法与单环单水头法(P＜0.05);单环双水头法测得Ks值均随坡度的增加而增加,而单环BEST法测量结果与之相反,随着土壤质地由粗变细,坡度的影响程度(回归线斜率)有降低趋势;单环单水头法(10 cm)测量Ks值与单环双水头法完全一致,在土壤水力学参数确定后,可替代单环双水头法.当坡度＜10°时,3种方法测量的Ks与无坡度Ks无显著差异,当坡度＞10°时,差异显著(P＜0.05).因此,坡度显著影响3种测量方法测算的Ks值,单环BEST法不适合测量坡地Ks,当坡度＜10°时,单环双水头法与单环单水头法(10 cm)可测量计算3种类型土壤Ks.%[Background] Soil saturated hydraulic conductivity (Ks) of sloping field is a key parameter to predict soil and water losses,but Ks is mostly measured on the flat land.Therefore,directly measuring saturated hydraulic conductivity on slopes is practically important.The objective of this paper is to study the effect of slope gradient on Ks by three single-ring infiltrometer methods in order to select a suitable method for slope land.[Methods] The slope gradients of 0,5°,10°,15° and 20° in sandy soil,Loessial soil and Lou soil were selected and Ks was measured by three single-ring infiltrometer methods (i.e.,two-ponding depth,one-ponding depth and BEST methods),which usually were used for flat lands.All measurements were conducted on undisturbed soil.[Results] 1) On flat soil surface,all three methods obeyed the same order for Ks of different soils as sandy soil ＞ Loessial soil ＞ Lou soil.The Ks of three soils by single-ring BEST infiltrometer were 2.9,2.1 and 4.5 times,which were larger than those by single-ring two-ponding depth infiltrometer.If cutting-ring infiltrometer was taken as standard,single-ring BEST infiltrometer significantly overestimated the Ks of the Loessial and Lou soil,but the results by single-ring two-ponding depth infiltrometer and single-ring one-ponding depth (10 cm) infiltrometer were close to that by cutting-ring infiltrometer.2) Ks measured by single-ring two-ponding depth infiltrometer increased with the increase of slope gradient and there was a significant linear correlation between them.The Ks of three soils by single-ring BEST infiltrometer decreased with the increase of slope gradients and this method was affected distinctly by slope gradient due to the change of the ponded water area inside the ring.3) Under flat ground condition,the results of single-ring oneponding depth (10 cm) infiltrometer were comparable to single-ring two-ponding depth infiltrometer,but the single-ring one-ponding depth (5 cm) infiltrometer overestimated the results.4) In sandy soil,Loessial soil and Lou soil,there was no significant difference of Ks between slope ＜ 10° and flat land by above 3 methods,but significant while slope ＞ 10° (P ＜ 0.05).[Conclusions] Therefore,single-ring BEST infiltrometer is not suitable for measuring Ks in sloping field.Single-ring two-ponding depth infiltrometer or single-ring one-ponding (10 cm) depth infiltrometer can be used to correctly measure Ks if the slope is ＜ 10°.Furthermore,the calculating equations for saturated hydraulic conductivity by these sing-ring methods should be revised for the three soils in the loess regions if the slope gradient is ＞ 10°.