The Influence Of The Grassland Enclosure Years On The Soil Infiltration Capacity In Yunwu Mountain

Grassland resources are the important resources in arid and semi-arid areas.The rainfall intensity in the Loess Plateau is much higher,which require higher infiltration capacity of soil transform more rainfall to grassland system.In this study,grasslands with different enclosure years(0,2,13,30,38 years)in Yunwu Mountain of Ningxia were selected.The physical and chemical properties and soil infiltration rate of the soil samples were measured,and the influence of land enclosure on soil physical and chemical properties and infiltration capacity was analyzed.The main factors affecting the soil infiltration capacity in Yunwu Mountain and the correlation between the factors were explored,and the effect of enclosure on Yunwu Mountain was preliminarily evaluated.The results show that:(1)The enclosure measures changed the basic properties of the soil.In the particle composition,the farmland is generally rich in clay,and the soil particle size is small;once the farmland is abandoned,the sand will increase immediately,and the phenomenon of desertification will appear.With the extension of the enclosure time,the silt and clay will increase again.The soil bulk density decreased with the increase of enclosure years.The soil bulk density of farmland before the farmland was the largest,continued to decrease after enclosure,and the 38-year-old sample plot was the smallest,and the total soil porosity showed a completely opposite performance;The water content increased,and the soil moisture content of the grassland was the highest after30 years of enclosure;the content and average particle size of soil water-stable macroaggregates increased with the increase of enclosure years,and the content of water-stable macroaggregates after enclosure for 30 years At most,it has decreased since then.With the increase of enclosure years,the number of soil macroaggregates increased slowly,and the fractal dimension increased.After 30 years,with the decrease of microaggregates,the fractal dimension gradually decreased.The change trend of soil organic matter content and aggregate content was consistent.With a limit of 30 years,after that,the grassland has failed,and the mechanical composition of the soil has been coarsened again.Comparing the plots with different fencing years,many basic properties of grassland with 30 years of fencing were better than other fencing years.(2)With the increase of enclosure years,the root biomass in the 0-30 cm soil layer showed a decreasing trend.Grassland enclosed for 2 years>13 years’>30 years’>38years’>farmland.And with the increase of enclosure years,the root biomass between different soil layers is narrowing.The root length density changed periodically with the enclosure years:grassland enclosure for 13 years>2 years’>30 years’>38 years’>farmland,and decreased with the deepening of soil depth.Under the closed conditions,the root development ability of grassland gradually got weakened.(3)The initial soil infiltration rate of the 5 plots was the fastest in the 13 years’grassland,and the slowest in the 2 years’grassland;the stable infiltration rate and average infiltration rate were the fastest in the 30 years’grassland.The cumulative infiltration was as follows:30 years’grasslands>38 years’>13 years’>2 years’>farmland.In conclusion,the initial infiltration rate of the 30-year-enclosed grasslands was at a relatively high level,and the stable infiltration rate,average infiltration rate and cumulative infiltration amount were all the best.(4)The Horton model(R~2:0.187～0.793)is more suitable than the Kostiakov model(R~2:0.667～0.856)for describing soil infiltration process in the soil of the enclosed grassland in Yunwu Mountain.The most suitable fitting models for the soil infiltration rate curves of five plots are inverse function models which R~2 ranges in 0.796～0.926.(5)In the 0-30 cm soil layer,the greatest influence on the soil infiltration rate of the 30-year-old grassland were the content of water-stable macroaggregates,soil moisture content,and soil organic matter content.There was a very significant positive correlation between soil water content and soil organic matter content,and significant negative correlation with soil bulk density(P<0.01).There was a significant positive correlation between soil organic matter content and soil water content(P<0.01),and a significant negative correlation(P<0.01)with the dimension of soil aggregate.This study showed that the improvement of soil physicochemical properties reached a peak when the enclosure measures were implemented for about 30 years,including soil infiltration.After that,soil water conductivity was degraded too,reflected that the period of enclosure should not be too long.Therefore,the grassland should be used reasonably to prevent the degradation of soil quality.