Depth Influence Of Grassland-farmland Boundary Based On The Hydrothermal Coupling

The agro-pastoral ecotone of China distributes from northeast to southwest across northern China,which is an important area of water conservation.Meanwhile,the agro-pastoral ecotone prevents the desert from northwest to southeast,and it is an important ecological barrier if central and eastern regions.The agro-pastoral ecotone has obvious variability and ecological vulnerability,and with the growing number of population and requirement of society,grassland in the agro-pastoral ecotone was converted to farmland.Natural grassland-cropland boundary(Guyuan county,Zhangjiakou)in Hebei Province(northern agro-pastoral ecotone)and cultivated grassland-cropland boundary(Maiping county,Guiyang)in Karst areas of Guizhou Province(southern agro-pastoral ecotone)were chosen as research objects to study(1)Dynamic monitoring soil moisture and soil temperature of different seasons in studied area;(2)Determine the depth influence of soil moisture,soil temperature and hydrothermal coupling of grassland-cropland boundary;(3)According to the depth influence of oil moisture,soil temperature and hydrothermal coupling boundary to divide different functional systems,and compare the variation of soil moisture and soil temperature among different functional systems.This study has reference value in the sustainable development of grassland animal husbandry,and also provided theory references and practical measures for enriching the boundary theory and the project of ―returning cropland to grassland‖.The results showed that:(1)There existed cultivated grassland-cropland compound functional area in southern agro-pastoral ecoton,which was also called the depth influence of boundary.the topsoil moisture of cultivated grassland was higher than that of cropland in studied area,and the change trend of topsoil moisture of four seasons in a year showed as ―high-low-high‖,indicating that the spring,summer,autumn and winter was the storage period,consumption period and recovery period of soil moisture,respectively.It was concluded that the position of soil moisture interface coincided with the position of landscape interface in studied area,the depth influence of soil moisture boundary from spring to winter was 41 m,29 m,24 m and 28 m.And the change rule was ―wide-narrow-wide‖ in a year,the depth of edge influence variation of soil moisture boundary in cropland system was consistent with total width of boundary,while the depth of edge influence was narrower and narrower in cultivated grassland system as seasons passed.(2)The width variation of soil temperature boundary in cultivated grassland-cropland(southern agro-pastoral ecoton)was changing with the seasonal shifts and soil temperature changing,and the width of cultivated grassland-cropland boundary changed from wide to narrow,which was 37,32,27 m and 24 m in spring,summer,autumn and winter,and it also indicated that the width of soil temperature interface in cultivated grassland system was changed consistent with the total width of the cultivated grassland-cropland boundary,which was categorized to gradual changing type boundary.The average soil temperature of the cropland functional area,the cultivated grassland-cropland compound functional area and the grassland functional was 14.0,14.1℃ and 13.9℃,respectively.(3)The soil moisture of grassland in four seasons were 60.7%±0.31,23.6%±0.20,19.7%±0.20 and 70.4%±0.19,respectively,which were higher than in cropland area;Soil temperature in grassland was lower than in cropland in summer and autumn,while it was completely opposite in winter and spring;Depth influence of seasonal edge boundary of cultivated grassland-cropland were 25 m,28 m,34 m and 29 m,respectively,the changes of boundary depth present as ―narrow-wide-narrow‖.(4)The width variation of soil moisture boundary in natural grassland-cropland(northern agro-pastoral ecoton)was changing with the seasonal shifts and soil moisture changing,and the depth influence of soil moisture boundary in spring,summer and autumn was 29 m,12 m and 22 m.It was concluded that the position of soil moisture interface coincided with the position of landscape interface in studied area.We can divide the natural grassland-cropland boundary into 3 functional systems: natural grassland functional system,natural grassland-cropland compound functional system and cropland functional system.(5)Depth influence of soil temperature in natural grassland-cropland(northern agro-pastoral ecoton)in spring,summer and autumn was 24 m,16 m and 30 m,which showed that the width of soil moisture boundary in autumn was widest and in summer was narrowest.(6)Depth influence of hydrothermal coupling in natural grassland-cropland(northern agro-pastoral ecoton)in spring,summer and autumn was 28 m,15 m and 26 m,which showed that the width of soil moisture boundary in spring was widest and in summer was narrowest.(7)Based on above results,we suggest that should set the width of 13-17 m to have grassland-cropland intercropping when regarding the policy of ―returning cropland to grassland‖ in southern agro-pastoral ecotone,while in northern agro-pastoral ecotone the width of 8-14 m to have grassland-cropland intercropping should be set to meet the requirement of soil moisture and soil temperature.