Quantitative studies on soil macropores under artificial Chinese pine(Pinus tabuleaformis Carr.)forest in loess hilly region

The radius,number and distribution of soil macropores under artificial Chinese pine(Pinus tabuleaformis Carr.)forest were quantitatively researched by the water breakthrough curve and Poiseulle equation.The radius of soil macropore,which is defined as the pores between field capacity and saturated water content,is 0.2～3 mm,of which the macropores with the radius larger than 1mm account for only 2.2% of total macropore number.And there are more macropres in the upper layers of soil profiles than those in the lower layers.The weighted mean radius of macropores in the upper layers is larger,and is gradually decreased along with the soil depth.The ratio between the macropore area and water through sectional area is 1.27%～18.13%,and the ratio is less than 5% for most samples.The slope position,gradient,shape and direction intensively affect soil macropores.Although soil macropores account for small portion of the soil volumes,there is a remarkable power function relation between the mean radius of soil macropores and water flux,saturated hydraulic conductivity.The mean radius determines 77% and 75% variances of water flux and saturated hydraulic onductivity,respectively.The mechanics of intensifying soil penetration by plants is the effect of preferential flow,which is produced by soil macropores formed by roots.