Variation and dynamics of soil properties of ordinary chernozem in the Saratov region

Based on data from an agrochemical survey using GIS technologies at test site No. 2 in 2009-2016 within the framework of the general scheme of soil-ecological monitoring of the Saratov region, an assessment was made of the dynamics and spatial variation of soil properties of ordinary chernozem, depending on the steepness and exposure of the slope. Soil and agrochemical characteristics in conditions of a pronounced relief demonstrate a certain dependence on the location and are very variable over time. Soil sampling on an area of more than 2000 hectares using navigation equipment made it possible to obtain agrochemical cartograms in GIS and analyze them using zonal statistics, taking into account a digital elevation model. The spatial variability of soil properties is often lower in leveled areas or short transition sections of the slope, while the maximum variability is noted on steeper slopes. The highest values of indicators are typical for flat watershed surfaces, which are the most fertile, however, the closest relationship between humus and other agrochemical indicators was noted just on steeper slopes. The variability of fertility indicators on differently directed slopes was within 28–36 % for P2O5, 20 % for K2O, and 4–6 % for pH. The greatest differences in the variability of the polar slopes along the survey tours are noted for the content of humus in the soil. In 2009, the coefficient of variation was 19 and 30 %, and in 2016, 11 and 24 % on the slope of the northern and southern exposure, respectively. A retrospective analysis showed that the highest rates of decline were noted for the content of humus in the soil and the reaction of the environment on gently sloping slopes (by 2 and 1.5 times, respectively) relative to the average change in the massif. For mobile forms of phosphorus and potassium, the maximum decrease was noted on gentle slopes.