SPATIAL VARIABILITY IN SOIL FERTILITY RELATED TO THE "FERTILE ISLANDS" EFFECT OF VITEX NEGUNDO

Vitex negundo shrubs serve as both windbreaks and soil stabilizers and can aid in soil water retention and improve soil nutrients in the soils of arid and semi-arid regions. To reveal the factors underlying these functions of Vitex negundo, this study analyzes the total nitrogen, organic matter and available phosphorus contents of soil exposed to the "fertile islands" effect of Vitex negundo and investigates the correlating variability in spatial structure. The results show significant differences in soil nutrients at varying horizontal distances from the main stem of the shrub, and the richness of soil nutrients gradually declines with increased distance from the main stem. The results also demonstrate that total nitrogen and soil organic matter typically decrease from the surface to the lower levels. Analysis by Kriging interpolation indicates that soil strata nearer to the surface contain greater nutrient richness than deeper soil. Hence, the results indicate that Vitex negundo's "fertile islands" effect causes great variability in spatial structure. Analyzing this variation will contribute to efforts to improve local ecological sustainability.