Heterogeneity of Soil Properties within a Single Plot: A Case Study of Black Soils in the Dry Steppe Zone of Stavropol Krai, Russia

Soil resources are natural strategic resources and national wealth. Stavropol Krai is an important agricultural region of Russia, which produces 8% of grain, 4% of sunflower, 5% of sugar beet, 1% of fruits and berries, 3% of meat and 2% of dairy products. It is necessary to examine the lands of the Stavropol Krai, in order to consider the main directions of strategic land management in facing the challenge of sustainable development of agricultural environmental management. The object of the study is a field with a total area of 241 ha, located in the dry zone—northern part of Stavropol Krai, the contours of the field completely lie in the area the predominant black soil contour (Calcic Kastanozem). The land management was the rotation of winter wheat with fallow. Arable horizon of black soils sampling was carried out on a square grid with a step of 100 m. According to the soil organic matter (SOM) content in the studied field, there is a progradation, the revealed degradation of pHKCl belongs to the 1st and 2nd degrees of degradation. Research has shown that taking the spatial variation of soil properties into account it is possible to determine the degree of soil properties indicators worsening in space within a field, herewith, it is insufficient to consider soil properties worsering or improving only by comparing average values. We compare the two approaches using pHKCl indicator: (1) comparing the average value with the reference—Kastanozems of the Ciscaucasia zone, (2) comparing the interpolated data using the ordinary kriging; and then calculate the relative amount of investment for improving soil properties. The investments when comparing the average value with the reference—Kastanozems of the Ciscaucasia zone, three times higher than investments considering natural variation of soil properties in space by interpolated kriging data. Our example showed that there is uncertainty in determining the quality of land due to the natural variation of soil properties in space: in the natural environment, everything is unevenly distributed; any soil property has variation within one soil contour in agricultural systems, therefore to consider soil degradation by comparing average values allows to improve the estimates.