| Studying the changes of soil physical properties in the process of grassland restoration has important scientific value for the ecological environment construction and soil quality evaluation of the Loess Plateau.In this paper,the Ansaifang lacustrine basin in the forest steppe zone and the Shenmu Liudaogou in the grassland zone were selected as the study area.Based on the combination of field test and laboratory analysis,the effects of restoration process of grassland on soil physical properties such as soil porosity,bulk density and agglomerate etc.were studied.Based on statistical methods,the key soil physical properties indicators driving grassland restoration changes were screened.The soil physical quality comprehensive index was used to quantitatively evaluate the impact of grassland restoration on soil physical properties,aiming to provide scientific basis for vegetation construction on the Loess Plateau.The main conclusions are as follows:(1)The restoration grassland can significantly change the structural characteristics of the soil.There was no significant difference in soil texture in the forest steppe zone,all of which were silty loam.Soil bulk density and capillary porosity decreased with the increase of recovery period of grassland.Total porosity,aeration porosity,the content of water stable aggregate >0.25 mm and MWD increased with the recovery period of grassland.The content of water stable aggregate>0.25 mm and MWD reached a steady state after 30 years of restoration of the grassland.The soil bulk density ranged from 1.04 to 1.45 g/cm3.Compared with farmland,soil bulk density decreased by 4.2?2.6?2.2 and 5.3 percent.Capillary porosity decreased by 12.1%,32.4%,23.9% and 29.5%.Total porosity increased by 1.2%,1.2%,3.8% and 6.2%;Aeration porosity increased by 9.9%,13.1%,16.7% and 20.9%.The content of water stable aggregate >0.25 mm increased by 49.4%,24.6%,80.2% and 83.6%.The MWD increased by 108.1%,63.1%,289.0% and 271.2%.The soil in the steppe zone was silt loam and loam.The soil bulk density was significantly reduced and the total porosity,aeration porosity,the content of water stable aggregate >0.25 mm and MWD increased significantly.The capillary porosity shown the increased-decreased-increased trend with the grassland restoration.The bulk density,the content of water stable aggregate >0.25 mm and MWD tended to be stable after 30 years of grassland recovery.The soil bulk density in the steppe zone ranged from 1.26 to 1.62 g/cm3,and the soil bulk density decreased by 3.4%,6.0%,6.1% and 11.6%;the total porosity increased by 10.9%.13.2%,12.1%,and 24.9%;aeration porosity increased by 1.8%,3.1%,11.8%,and 24.5%,and the content of water stable aggregate >0.25 mm increased by 27.5%,48.8%,72.1%,and 63.7%.The MWD increased by 107.3%,125.5%,155.5% and 167.8%.(2)The restoration process of grassland significantly changed the hydrological and physical characteristics of soil.The soil saturated water content and field water holding capacity in the forest steppe zone increased with the increase of the recovery period.The soil water holding capacity and specific water capacity of the grassland showed the characteristics of decreasing first and then increasing with the increase of the recovery period.The soil water holding capacity reached a steady state after the grassland recovered for 20 years.In grassland zone,the saturated soil moisture content and field water holding capacity of restoration grassland fluctuated with the increase of grassland restoration years.Soil water holding capacity and specific water capacity increased first and then decreased,and peaked in the 10 th year of restoration of grassland.The saturated soil moisture content of grassland in the 10,20,30 and 40 years increased by 15.4%,22.5%,10.4% and 30.5%,respectively,and the field water holding capacity changed by 22.7%,18.3%,-4.7% and-0.6%.(3)Restoration of grassland significantly improved soil infiltration capacity.Compared with farmland,the saturated water conductivity of grassland in the forest steppe zone increased by 109.9%,25.9%,148.1% and 121.8% in 10,20,30 and 40 years respectively.The grassland zone increased by 83.6%,234.7%,35.1% and 73.2% in 10,20,30 and 40 years respectively.The soil saturated hydraulic conductivity and stable infiltration rate in the forest steppe reached a stable state after 30 years of restoration.The Horton model had the best simulation effect on the infiltration process in the two zones.The order of the infiltration rate of the forest steppe zone was: 40 years grassland(2.089mm/min)>10 years grassland(1.997mm/min)>20 years grassland(1.786mm/min)>30 years grassland(1.777mm/min)>farmland(1.729mm/min);stable infiltration rate of grassland zone: 40 years grassland(1.542mm/min)> 30 years grassland(1.246mm/min)> 20 years grassland(1.181mm/min)>farmland(0.923mm/min)>10 years grassland(0.740mm/min).(4)A saturated hydraulic conductivity transposition function was constructed.Soil total porosity,non-capillary porosity,the content of water stable aggregate>0.25 mm,clay content and silt content were the main factors affecting soil saturated hydraulic conductivity.The transposition function of soil saturated hydraulic conductivity in forest steppe zone can be derived from aeration porosity(AP),water-stable aggregate >0.25 mm content(WSA),and silt content(Silt): Ks1=0.005 WSA + 0.016 AP-0.015 Silt + 0.544(R2=0.534,P<0.01);the transposition function of soil saturated hydraulic conductivity in grassland zone can be derived from total porosity(TP),water stable aggregate >0.25 mm content(WSA),clay content(Clay): Ks2 = 0.005 TP + 0.004 WSA-0.011 Clay-0.022(R2 = 0.439,P < 0.01).(5)Restoration of grassland significantly improved soil physical quality,and soil bulk density,aeration porosity,the content of water-stable aggregate >0.25 mm,field water holding capacity and soil saturated hydraulic conductivity were key soil physical property indicators in response to restoration of grassland in loess area.Compared with farmland,the soil physical quality index of 10,20,30 and 40 years forest steppe zone increased by 657.4%,928.1%,936.9% and 957.4% respectively;the grassland zone increased by 5139.2%,4613.5%,11004.5 % and 17438.6%. |
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