Spatial and temporal variability of available phosphorus content in the arable soil layer according to different methods

The purpose of the article is to highlight the results of assessing the stability in time and space of the content of mobile phosphorus compounds in the soil within the arable layer on the land plots. The studies were carried out during 2018-2020 on two fields of the experimental farm "Grakovskoe" NSC "ISSAR named after O.N. Sokolovsky "in the Kharkiv region. The soil cover of one of the fields is made up of Chernozem podzolized (Chernic Phaeozem) in combination with Dark gray podzolized soil (Luvic Greyzemic Phaeozem), and the second field is Chernozem typical (Haplic Chernozem) with eroded and highly moistened varieties. Each field was divided into 24 plots, from which mixed soil samples were taken from 7 individual samples from a layer of 0–30 cm twice a season – in April–May and in October–November. On the soils of the podzolized row, a high amplitude of fluctuations in the pH values of salt was found during 3-year observations – from 4.4 to 5.2. As a result, the parameters of soil saturation with mobile phosphorus, determined by the methods of Chirikov and Machigin, were significantly different. In a field with chernozem, the typical measurement results for both methods were similar. The results of the analysis of the content of mobile phosphorus in the soils of the field according to the average values of the aggregate of individual samples did not show significant seasonal differences. However, on each of the fields, there were separate locations with higher values both according to the Chirikov method and the Machigin method, regardless of the sampling season. Along with this, in both fields there are locations where two methods of determination show different trends in the spatial distribution of the content of mobile phosphorus, which indicates the artificial nature of such heterogeneity. This confirms the hypothesis about the presence of a stable and temporarily artificial component of the spatial heterogeneity of the phosphate state of soils.