| The animal activity, the plant root system extension or rotten as well as the soil physics and the chemical action, causes the soil pore's nonuniformity, exists many macropores. Water and its solute pass macropores in soil fast migration, which is preferential flow. Macropores in the soil is the universal existence phenomenon, Preferential flow widely exists in the soil, plays the leading role in the process of moisture infiltration. The research preferential flow may deepen understanding the rule of the soil moisture infiltration with the solute migration. The preferential flow can impact further on runoff, supply of soil moisture and soil erosion. So it is important in study on soil and water conservation, soil moisture and groundwater. It has been one major study part of agriculture, environmental science and ecology. Root channels are important component of macropores in the soil. Research on distributing of roots and the preferential flow can strengthen understanding of forming mechanism of the preferential flow, and provide the comprehensive control of water and soil conservation.In this paper, three kind of forest lands in the 0~30cm soil layer under the Populus davidiana forest, the Pinus tabulaeformis forest, and the shrub on Loess hilly region was take as the research object. The method of digging was applied to investigate the plant roots system's spatial distribution. The method of dye was applied to investigate the preferential flow. The relation of roots and preferential flow was analyzed. The findings indicated that:(1)Between three kind of forest lands, roots long density, the root volume and the root system quantity have a bigger difference, which showed that: the Populus davidiana forest > the Pinus tabulaeformis forest > the shrub. The root long density and the root system quantity have the tendency along with the depth which decreases progressively. This kind of change of root system volume in the Pinus tabulaeformis forest land is not certainly obvious. Looked from the different diameter size of root system, the characteristic is that: the proportion of length and quantity of thin root system (< 3 mm diameter size) are much more than that of thick root system (> 3mm diameter size). The proportion of root volume of coarse root is much more than thin root, namely characteristic of the thin root mainly manifests length and quantity of the root system, the thick root manifests the volume.(2)Ecological niche index of root system in three forest lands presents the more obvious drop tendency along with the depth of soil layer. The ecological niche index of thin and thick root are higher than moderate diameter roots under the Populus davidiana forestland and the Pinus tabulaeformis forestland. The shape of ecological niche index of root system presents the obvious U characteristic along with the root system diameter size distribution, but the root ecological niche index of shrub displays the obvious counter- J characteristic along with the diameter size distribution. Ecological niche index of root system of community showed that: the Populus davidiana forest > the Pinus tabulaeformis forest >the shrub.(3)There were obviously differences for the scattered degree of root system in three forestlands. The root scattered indexes of Populus davidiana and shrub were up to the most value at 15 cm soil depth, then the index decreased; but the scattered index had no obviously change for Pinus tabulaeformis. The root scattered indexes were all less than 1 for soil surface or deeper layer, this showed plant root in soil was a cluster distribution.(4)Three forest lands all exists the obvious preferential flow in the soil. As a result of existence of the soil preferential flow, part of precipitation infiltrate quickly to the soil, supplement the soil moisture, and decrease the surface runoff to the certain extent. From the findings, the infiltration depth of preferential flow on loess hilly region generally is about 20～40cm. Macropore is main cause of preferential flow. Macropores formed by root system have obviously influence on soil moisture movement on Loess hilly region. Because the plant root system mainly concentrates in the soil shallow layer, the depth of soil moisture infiltrated is shallower, which has affected the in-depth soil moisture fast supplies.(5)The most depths of infiltration caused by preferential flow are different in different forestland. The finding showed that: the greatest depth is the Populus davidiana forest, next is the Pinus tabulaeformis forest, then the shrub, respectively 44cm, 40cm and 30cm.This is because the Populus davidiana forest form the more plants root system to strengthen the moisture to infiltrate. The depth of infiltration in the bush land is deeper, besides plant root system's influence, but also as a result of influence of deposition caused by the soil upper slope foothill, which cause soil including more broken stones and the sand grains, possibly forming many macropores. Influence of different spraying way on preferential flow is different. When intensity of spraying is bigger, the earth surface has catchment, moisture infiltration is deeper. This explained that intensity of the precipitation has influence on soil moisture infiltration.(6)On vertical section, the more and centralized distribution root system is, the deeper the Brilliant Blue moves, the bigger the dyeing region is. There are obviously different for root system between dyeing region and non-dyeing region. The quantity, the volume and the root long density of root system are much more in dyeing region than in non-dyeing region. This explained root system has obvious impact of enhancement on moisture infiltration.(7)The degree of influence of the root long density, the root quantity and the root volume respectively on the soil moisture infiltration all showed: the Populus davidiana forest >the shrub > the Pinus tabulaeformis forest. In three forest lands, the influence of root density and root quantity on the soil moisture infiltration is more than that of root volume. The influence of root system with different diameter size on infiltration is different. The influence of thin root on the soil moisture infiltration is more than that of thick root. The influence of ecological niche index of root system on infiltration showed that influence of the Populus davidiana forest land and the Pinus tabulaeformis forest land is more than the shrub. |
PDF Full Text Request