Impacts Of Vegetation Restoration On Soil Physical And Chemical Properties In The Loess Hilly Gully Region Of Loess Plateau

The ecological environment of the Loess Plateau is fragile.The soil erosion is serious.The ecological environment is improved;the vegetation coverage in the Loess Plateau has increased and the land use and land cover have changed significantly since the implementation of the “grain for green” project in 1999.In this paper,we chose the typical county of returning farmland to forest(grass)In semi arid region-Wuqi County of Shanxi Province as study area.The different abandoned years(5a,15 a,40a)of abandoned land and different abandoned models(forest of Hippophae rhamnoides Linn at15 a,forest of Armeniaca sibirica(L.)Lam at 15 a and 40a)were studied.The research mainly included the following indexes: characteristics of surface communities such as vegetation cover,species and quantity;soil physical and chemical properties such as soil bulk density,mechanical composition,aggregates,water holding capacity,infiltration rate,organic matter content.The effects of plant communities on soil physical and chemical properties and soil infiltration properties were investigated by means of space replacement time.It could provide the theoretical basis for the ecological hydrological process of vegetation restoration in the Loess Plateau,and provide hydrological parameters for model simulation.It can provide scientific support for regional land use planning and ecological environment construction.The main conclusions are as follows:(1)The herbaceous communities in this area are mainly perennial vegetation types,such as composite and rosaceae.The forest of Hippophae rhamnoides grows vigorously,and the herbaceous vegetation under the forest is scarce.The forest of Armeniaca sibirica(L.)Lam had little effect on the growth of herbaceous vegetation.With the increase of the number of years of returning farmland into grassland,the Margalef index(richness index)of herbaceous community increased,and the Shannon-Wiener index(diversity index)firstly increased and then decreased,and the Pielou index(evenness index)changed little.Evenness,richness and diversity index of herbaceous community of the forest of Armeniaca sibirica(L.)Lam was not sifnificant difference with that of natural grassland.(2)The soil texture in the study area is silt loam.There was no significant difference in soil size composition under different cover.With the increase of natural recovery time,the fractal dimension D increased,but there was no significant difference.The grass contains more water than the forest of Hippophae rhamnoides and Armeniaca sibirica(L.)Lam.natural water content with the increase of soil depth increased firstly and then decreased.There was no significant change in soil bulk density under the different vegetation cover.With the increase of years of returning farmland into grass,the content of large particles of water-stable aggregates(> 0.25mm)increased.MWD of woodland was greater than grassland in the 0-120 cm profile.With the increase of depth MWD and the content of water stable aggregates of > 0.25 mm decreased.(3)The change of soil organic matter was consistent with total nitrogen.With the increase of years,organic matter and total nitrogen content decreased firstly and then increased.The order of content of organic matter and total nitrogen under different coverage patterns was: Armeniaca sibirica(L.)Lam>Hippophae rhamnoides> grassland.Except for 5 years,the content of organic matter and total nitrogen decreased with the deepening of soil layer.There was no significant difference in the total phosphorus content under different coverage.(4)In the semi-arid area,under the silt loam background,initial infiltration rate,stable infiltration rate and cumulative infiltration was no significant difference until the conversion of farmland into 40 a.Infiltration rate and cumulative infiltration in woodland was higher than that in grassland but the ratio(initial infiltration rate / steady infiltration rate)was less than that of grassland.The initial infiltration rate and steady infiltration rate)less than 6 plots of grassland;on the whole,the initial the infiltration rate and steady infiltration rate was consistent with the increase of depth,the infiltration rate was fluctuant decline.With the increase of depth,the infiltration rate of 6 plots decreased.In the whole process of infiltration,the changes of Ks occur in 5 hours and it reached stability.Infiltration process simulation results showed it used the Kostiakov formula better.The indexes of correlation analysis indicated that organic matter,bulk density and water-stable aggregates and other indicators were related.The various indicators were response to vegetation restoration process.