Probabilistic nature of humus content and estimation of heterogeneity at mapping of soils on basin principle

Abstract

Estimation of the probabilistic nature of humus content, its spatial heterogeneity and dynamics of changes are made on the example of Chernozem ordinary in the system of four watersheds in the river basin of Aidar in Lugansk region of Ukraine. It was used for the calculations humus content for two periods - 1970 and 2011. It was found that the loss of humus content for 41 years is 0.015 and 0.020 % within the limits of Bilolutsky and Starobilsk watersheds and 0.024 and 0.029 % in the watersheds areas of Kuryachivsky and Bakhmutovsky. The stabilization of humus content in the upper part of the basin (4.5 %) and its decrease below the current from 6.13 → 4.79 → 4.10 % (1970) to 4.08 → 4.07 → 3.55 % (2011). As a whole, in the soils of the Aidar River basin since 1970 there was a decrease in the content of humus from 4,58 ± 0,13 % (1970) to 4,03 ± 0,05 % (2011). The statistical analysis of the data was carried out according to the following indicators: number of observations (n); mean value (хmean); dispersion (S2); standard deviation (S); variation coefficient (Cv); absolute error (Sxmean); median (M); asymmetry (A); excess (E). The analysis of the probability of the nature of the humus content is performed according to the following criteria: humus content index ‒ the ratio of actual humus content in the control point to the arithmetic mean; theoretical curve of theoretical probability curve (Pearson type III curve), constructed by arithmetic mean, coefficient of variation (Cv) and coefficient of asymmetry (Cs). It was found that the probability of displaying average (typical) values of humus content on the investigated objects is determined by the system of catchments and does not exceed 50 %. At the same time, in the case of values of the coefficients of variation Cv = 10,5 and 12,1 % (Starobilsk and Belolutsky watersheds, respectively), the deviation of the probabilities from the average content of humus (4.05 and 4.38 %) in the direction of decline does not exceed 40 % of the territorial distribution, and in the case of values Cv = 18.6 and 19.7 %, the probability and deviation from the typical level (3.50 and 4.05 % humus in the Bakhmut and Kuryachiv watersheds) is 60 %. The spatial variability of the humus content in the soils of all four catchments does not exceed the average (CV = 10.47 ‒ 19.65 %). According to the results of the analysis of the spatial distribution of soils by groups of humus content in four catchment areas, an integrated map of humus content in the basins of the Aidar River in general was constructed and the area of soils with different parameters was determined.