Effects Of Vegetation Types On Soil Aggregates And Infiltration Characteristics In Loess Plateau Gully Region

The soil physical parameters,soil aggregates characteristics and soil infiltration capacity under different vegetation types in Loess Plateau have significant differences,the paper is due to provide the basis for the selection of vegetation types to keep soil and water and the reasonable spatial layout in Loess Plateau Gully Region.In this paper,Changwu County of Shaanxi province in Changwu Tableland Gully Region was choosen as the study area,mainly local vegetation types were selected as objects,the 20-year locust forestland,the 20-year oriental arborvitae forestland,the 20-year apricot forestland and the abandoned grassland which is 20-year were chosen as plots.This paper was aimed to study the soil physical properties,root characteristics and soil aggregates properties under different vegetation types,and measure infiltration properties,the number of macropore and contribution of macropore to total flow of surface soil by the disc-permeameter.There were the results:(1)The soil physical properties and root characteristics under different vegetation types had significant differences.The water-stable aggregates,root biomass,root length density and root area index of the abandoned grassland were higher than those of the forestlands.For the factors affecting water conductivity of the 0-30 cm soil under the four vegetation types,the physical properties and root characteristics of the abandoned grassland were better than those forestlands.(2)The dry sieving 0.25-5 mm aggregates content of the 0-30 cm soil in four plots showed: the abandoned grassland > the apricot forestland > the locust forestland > the oriental arborvitae forestland,the wet sieving aggregates content showed: the abandoned grassland > the locust forestland > the apricot forestland > the oriental arborvitae forestland;the dry sieve aggregate mean weight diameter(MWD)and geometric mean diameter(GWD)showed: the oriental arborvitae forestland > the apricot forestland > the locust forestland > the abandoned grassland,the wet sieve aggregate MWD and GWD showed: the oriental arborvitae forestland> the locust forestland > the abandoned grassland > the apricot forestland,the dry sieve aggregate fractal dimension(D)showed: the locust forestland > the abandoned grassland > the apricot forestland > the oriental arborvitae forestland,the wet sieve aggregate D showed: the apricot forestland > the locust forestland?the abandoned grassland > the oriental arborvitae forestland.The results showed that the development of the soil aggregate structure and the stability of the soil aggregate were favorable to water conduction in the abandoned grassland,and the oriental arborvitae forestland showed the advantage of shaping large aggregates.The maximum value of organic carbon content in each particle dry sieving aggregate appeared in the <0.5 mm aggregate,it indicated that the smaller particle size aggregates were more conducive to the accumulation of organic carbon.(3)The infiltration capacity of four vegetation types were: the abandoned grassland > the locust forestland > the apricot forestland > the oriental arborvitae forestland,the result showed when the vegetation restoration year was 20,the infiltration capacity of the abandoned grassland was better than those forestlands,the abandoned grassland and the locust forestland could be more conducive to rainfall infiltration to maintain soil and water.The infiltration capacity of the oriental arborvitae forestland was obviously weak,which was related to the large aggregates content and the average size of the soil aggregates,it indicated that the large diameter aggregates had poor water conductivity.The Gardner exponential function can be used for fitting the hydraulic properties of the four plots surface soil by the pressure dependences.The porosity of the >0.5 mm pore of the four plots was 1.11%-1.61%,it showed the abandoned grassland > the locust forestland > the oriental arborvitae forestland > the apricot forestland.The contribution rate to the saturated infiltration of the >0.5 mm pore of the four plots is 55.4%-70.7%,it showed the apricot forestland > the oriental arborvitae forestland > the abandoned grassland > the locust forestland,it demonstrates the macropores can play important contribution to the infiltration.When the waterhead was 0 cm and-1 cm,the four types stable infiltration rate showed a significant positive correlation with the clay content,0.25-5 mm aggregates content,volumetric water content and root length density.The results of this study showed that the vegetation restoration in the Loess Plateau Gully Region should adhere to the combinationn of forestlands and grasslands.The grasslands and the locust forestland can rapidly improve the soil physical properties and hydraulic conductivities.The oriental arborvitae forestland has a certain effect to the formation of >5 mm aggregates,the water storage capacity of the apricot forestland is the best,but the soil and water conservation of the apricot forestland and the oriental arborvitae is insufficient.So the apricot forestlands and the oriental arborvitaes need be planted with locust forestlands and grasslands,taking into account the ecological,economic,and social benefits.