Soil physical-chemical properties and plant biomass in relation to microtopography spatial variability in saline-sodic soil area

In arid and semi-arid regions, microtopography is one of the important factors affecting saline soil properties and plant distribution.In order to further understand the spatial variation characteristics of soil physical and chemical properties and plant response to the saline-sodic soil under microtopography in Northeast China, the spatial variation characteristics of relative elevation, soil physical properties(bulk density, total soil porosity, soil mass water content), soil chemical properties(pH, electrical conductivity, sodium adsorption ratio) and plant biomass in the saline-sodic soil with typical microtopography characteristics were studied by combining classical statistics and geostatistics.The spatial distribution map was drawn by spatial interpolation.The classical statistics showed that the coefficients of variation of soil physical and chemical properties under the microtopography were less than 0.7, indicating moderate and weak spatial variation; The geostatistical analysis demonstrated that the nugget coefficients of soil physical and chemical properties were smaller than 75%, indicating moderate and strong spatial autocorrelation.In addition, soil physical indexes(mass water content) had a stronger spatial autocorrelation than soil chemical indexes(pH, electrical conductivity, sodium adsorption ratio).In other words, microtopography had a more intense effect on soil moisture.The spatial interpolation map exhibited that the spatial distribution of soil indexes was striped or patchy.The measured soil physical and chemical properties were significantly correlated with relative elevation, while plant biomass and relative elevation was negatively correlated.The correlation coefficient of microtopography to soil moisture was greater than that of soil physical and chemical properties, while the correlation coefficient was the least between microtopography and plant biomass.Therefore, it is suggested that the microtopography leads to the difference of soil moisture at different elevations on the slope, and then changes the soil physical and chemical properties, which indirectly affects the plant changes.The regression analysis showed that there was a quadratic function relationship between the soil physical and chemical indexes and the relative elevation, and the soil salinity reached the highest threshold with the lowest plant biomass when the elevation of the microtopography was 50~60 cm.The discovery of elevation threshold provides a theoretical basis for differential remediation and tillage management of saline-sodic soils.