| There has abundant water and heat resources in the low hilly area of red soil in Southern China,but the conflict between people and land was fierce and the intensity of agricultural development was high.The extensive forest and fruit development management in the area,the single measure layout,and the lack of optimized design and targeted management measures have led to serious soil erosion.The reasonable layout of soil and water conservation measures on terraced slopes affects runoff generation,rainfall infiltration,and water storage and retention capacity,which are the key factors to promote the development of forest and fruit industries.At present,domestic and foreign researches on the spatiotemporal distribution of moisture on terraced slopes mostly focus on a single land use structure or terrace type,and less focus on the impact of soil and water conservation measures on the hydrological function of slopes.This paper taked the navel orange development demonstration area in the Xiaoyang small watershed as the research area,and selected three types of land use structure slopes(optimize land preparation slope TA;traditional land preparation slope TB;erosion waste grassland,slope CK),four types of land use(optimize land preparation orchard A,traditional land preparation orchard B,waste grassland,and cropland)as research objects.Through topographic factors investigation,field disc infiltration test,lab tests and long-term soil moisture monitoring test by using TDR.After the red soil eroded inferior land was developed into terraced orchards,the effects of topography transformation and soil and water conservation measures on the physical and chemical properties of soil,infiltration performance and the spatial and temporal distribution characteristics of soil moisture in0?100 cm soil layer(0?20,20?40,40?60,60?80,80?100 cm)on slopes were studied,and combined with CCA(canonical correspondence analysis)to evaluated the main environmental factors affecting soil moisture distribution;At the same time,the response mechanism of soil moisture to rainfall on the TA slope was studied,and the feasibility of soil and water conservation measures to control nutrient loss on the slope was analyzed.The research conclusions can provide scientific basis for the rational allocation of land use resources,the optimization of the spatial layout of soil and water conservation measures,and the comprehensive management of soil and water loss.The findings are as follows:(1)Among these 3 slopes,soil properties such as soil saturated hydraulic conductivity in deep layer(K_s),capillary porosity,non-capillary porosity,sand content,and p H were significant(P<0.05)differences in different slope positions(top slope,upper slope,middle slope,lower slope,toe slope)and land use,soil bulk density,non-capillary porosity,and p H were extremely significant(P<0.01)differences between different soil layers.Through correlation analysis,it could be seen that soil bulk density and clay content were significant reduced after the waste grassland preparation,the non-capillary porosity and soil infiltration performance increased significantly,but the difference between the two terrace orchards was very small;Because of the highest soil clay content in cropland,its soil infiltration performance was the worst.(2)The changes of the surface soil saturated hydraulic conductivity and macroporosity between different slope positions was not obvious;under different land use types,the surface soil saturated hydraulic conductivity was represented as orchard A>orchard B>cropland>waste grassland,and the difference between orchard A and orchard B was small;Meanwhile,the surface soil large pores with diameter>0.5 mm of the two types of terraced orchard were higher than the waste grassland and cropland,and these large pores were the key to improving the surface soil water infiltration of orchard.(3)In the rainy season,the soil water content in different land use types was showen as cropland(0.4088 m~3/m~3)>orchard B(0.3227 m~3/m~3)>orchard A(0.3078 m~3/m~3)>waste grassland(0.2739 m~3/m~3),the terrain modification significantly(P<0.05)increased the infiltration performance of the soil to rainfall.CCA results shown that the soil moisture distribution in the rainy season was mainly affected by non-capillary pores,soil and water conservation measures have a weak effect on improving soil infiltration performance;In the dry season,the difference of soil water content between different soil layers was greater than in the rainy season,and the soil moisture content of the same profile showed an increasing trend from top to bottom,the soil water content in different land use types was showen as cropland(0.3524 m~3/m~3)>orchard A(0.1980 m~3/m~3)>orchard B(0.1475 m~3/m~3)>waste grassland(0.1380 m~3/m~3).The water content of the soil in the waste grassland and orchard B was greatly reduced,and the moisture content in the dry season was significantly lower than that in orchard A(P<0.05).The soil moisture distribution in the dry season was mainly affected by the land use types,and the influence of soil properties was weak.Among different slope positions,the soil water content in the rainy season and dry season gradually increased from the top to the bottom of the slope,and the differences between the upper,middle and lower positions of the three slopes were small.The soil water content variability is significantly greater than that in the rainy season.During the whole observation period,the soil water content of the 0?40 cm soil layer was mainly significantly affected by environmental factors such as land use types,porosity,and mechanical composition,while environmental factors had a weaker effect in deep soil.(4)The response range of the soil moisture content to the rainfall on the TA slope gradually decreased from top slope to toe slope,in different land use types was showen as waste grassland>orchard A>cropland,and the soil moisture content was shown as gradual downward trend from top to bottom in different soil layers;Under heavy rainfall(42.0mm/d),the response of soil moisture to rainfall was mainly controlled by the initial soil moisture content,and under small rainfall(24.2 mm/d)was mainly affected by K_s and non-capillary porosity;There was a small soil midstream on the slope-top waste grassland,orchards had a relatively impermeable layer in the 40 cm layer,but no soil midstream occurs.In this study,after the slope of the waste grassland was modified into a terrace,the soil infiltration performance and moisture were significantly improved,and the soil and water conservation measures deployed in the terrace also significantly improved the soil water storage and retention capacity of the terraced soil in the dry season.It showed that the land use structure design of TA slope and the spatial layout of soil and water conservation measures had significantly improved the ecological benefits of forest and fruit industry development. |
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