PATTERNS OF CHANGES IN THE SPATIAL STRUCTURE OF AGROCHEMICAL PROPERTIES OF ARABLE LIGHT GRAY FOREST SOIL DURING LONG-TERM OBSERVATIONS

The studies were conducted to assess changes in the spatial structure of mobile forms of nitrogen, phosphorus and potassium in the arable layer of light gray forest soil in the Republic of Tatarstan from 1965 to 2021. Long-term data from agrochemical surveys were processed using the method of geostatistical variogram analysis, reflecting changes in the dispersion of indicators with distance. Over the course of almost 60 years, there has been a noticeable change not only in the content of mobile forms of nutrients, but also in their spatial structure. The autocorrelation ranges (the distance of maximum similarity of the indicator in space) of mobile phosphorus in 1965 and 1975 were 185 and 205 m, respectively. By 1980, the value of this indicator increased to 459 m, and in 2011 it reached a maximum (778 m). The autocorrelation range of mobile potassium increased from 213 m (1965) to 439 m (2021), hydrolyzable nitrogen - from 266 m (1975) to 550 m (2021). Variagrams of hydrolyzable nitrogen in 1987 and 2011 indicate a regular change in space (spatial trend). The ratio of variogram elements (nugget/threshold), which is used to estimate the spatial dependence of the indicator (the mutual influence of the indicator based on its location in space), made it possible to conduct a comparative analysis of the spatial structure of the studied properties over time. For hydrolyzable nitrogen, the spatial dependence was moderate from 1975 to 1980 (nugget/threshold within 25...75%), and strong from 1987 to 2011 (nugget/threshold <25%). For mobile phosphorus, it was predominantly strong, with the exception of 1975 (moderate), and for mobile potassium - weak in 1975 (>75%), and moderate in 1965, 1980 and 1987. Compared to hydrolyzable nitrogen, mobile forms of phosphorus and potassium are characterized by a more stable spatial structure, but a tendency to increase the autocorrelation range is noted.