Search

In this study, we use classical and geostatistical methods to identify characteristics of some selected soil properties including soil particle size distribution, soil organic carbon, total nitrogen, pH and electrical conductivity and their spatial variation in a 5-year recovery degraded sandy grassland after two different grazing intensity disturbance: post-heavy-grazing restoration grassland (HGR) and post-moderately grazing restoration grassland (MGR), respectively, in Horqin steppe, Inner Mongolia, northern China. The objective was to examine effect of grazing intensity on spatial heterogeneity of soil properties. One hundred soil samples were taken from the soil layer 0–15 cm in depth of a grid of 10 m×10 m under each treatment. The results showed that soil fine fractions (very fine sand, 0.1–0.05 mm and silt + clay, <0.05 mm), soil organic carbon and total nitrogen concentrations were significant lower and their coefficients of variation significant higher under the HGR than under the MGR. Geostatistical analysis of soil heterogeneity revealed that soil particle size fractions, organic carbon and total nitrogen showed different degree of spatial dependence with exponential or spherical semivariograms on the scale measured under HGR and MGR. The spatial structured variance account for a large proportion of the sample variance in HGR plot ranging from 88% to 97% for soil particle fractions, organic C and total N, however, except for organic C (88.8%), the structured variance only account for 50% of the sample variance for soil particle fractions and total N in the MGR plot. The ranges of spatial autocorrelation for coarse-fine sand, very fine sand, silt + clay, organic C and total N were 13.7 m, 15.8 m, 15.2 m, 22.2 m and 21.9 m in HGR plot, respectively, and was smaller than in MGR plot with the corresponding distance of 350 m, 144.6 m, 45.7 m, 27.3 m and 30.3 m, respectively. This suggested that overgrazing resulted in an increase in soil heterogeneity. Soil organic C and total N were associated closely with soil particle fractions, and the kriging-interpolated maps showed that the spatial distribution of soil organic C and total N corresponded to the distribution patterns of soil particle fractions, indicating that high degree of spatial heterogeneity in soil properties was linked to the distribution of vegetative and bare sand patches. The results suggested that the degree of soil heterogeneity at field scale can be used as an index for indicating the extent of grassland desertification. Also, the changes in soil heterogeneity may in turn influence vegetative succession and restoration process of degraded sandy grassland ecosystem. [ABSTRACT FROM AUTHOR]

Horqin Sandy Land is one of the serious desertification areas in the semiarid zone of north China. Shrubs are the dominant plant species in this region and they play an important role in the wind erosion-prone fragile ecosystem. This study deals with the differences of some chemical properties in the soils under shrub canopies and from adjacent open spaces and analyses their characteristics in the shrub rhizospheric soils and bulk soils. The results showed that: (1) the concentrations of organic C, total N, and total P, and the value of electrolytic conductivity (EC) in the soils under the canopy of shrubs increased by 56%, 51%, 37%, and 51%, respectively, compared with those of the soils in open spaces, but there was no significant difference in pH between the soils under shrub canopies and open spaces; (2) shrub rhizosphere soils exhibited significantly higher contents of organic C, total N, and values of EC as well as a lower value of pH compared to the bulk soils, but there was no significant difference in total P between rhizosphere and bulk soils; (3) there were close relationships between the properties in soils under shrub canopies and the rhizosphere soils, indicating that the development of "fertile islands" are favorable to root growth and induce greater amount of rhizodeposition, and vice versa; and (4) soils under Artemisia frigida and Caraganda microphylla canopies and rhizospheres had significantly higher organic C and total N contents than those of Artemisia halodendron and Salix gordejevii. The results suggested that shrubs were of vital importance for the sequestration and accumulation of nutrients and maintenance of soil fertility in the Horqin Sandy Land ecosystem. [ABSTRACT FROM AUTHOR]