Spatial variability of soil properties in the floodplain of a river oasis in the Mongolian Altay Mountains

Abstract

In Mongolia, recent national policy pushed for the expansion and intensification of land use for crop and forage production, which may adversely affect soil quality of river oases. A better understanding of the small-scale variation of soil properties and the driving factors of soil quality are important for developing and refining site-specific agricultural management practices and for maintaining soil fertility. The current study hypothesized that spatial variability structure of ancient sedimentary processes override the actual variation of soil properties caused by land-use and environmental effects. The objectives were (i) to determine the small-scale variability of major topsoil properties within an exemplary river oasis in Western Mongolia, (ii) to assess the spatial structure of this variability (heterogeneity), and (iii) to identify factors driving the heterogeneity of soil biological properties. Within a four ha plot, 130 topsoil samples were collected in a constant 20 m grid and analyzed for major physico-chemical and microbial properties. The soil variability was assessed by descriptive statistics, the heterogeneity of properties by semivariogram model parameters, and heterogeneity driving factors by multiple linear regression analysis. Soil parameters showed a relatively high variability, particularly of CaCO3-C and EC (86% and 163%, respectively). In contrast to that, both parameters showed a relatively low heterogeneity (nugget to sill ratio of ≥0.67) whereas most soil parameter were characterized by a moderate or strong spatial dependency (nugget to sill ratio down to 0.2 as for microbial biomass C) and by relatively low range values (down to 37 m as for ergosterol and microbial biomass C), respectively. This small-scale heterogeneity with relatively many small patches reflected inherent soil factors of the floodplain, which had a strong influence on soil properties as the extensive land use in the river oasis Bulgan Sum Center did not lead to a homogenization of the fluvial depositions. Besides the minor salinization, which had a positive effect on ergosterol and basal respiration, SOC determined biological soil properties. This underlines the significance of SOC to preserve the scarce and susceptible agro-ecological resources of the river oasis in Western Mongolia and likely many similar ones across Central Asia.