The phosphate state of agrochernozems under soybean crops under conditions of application of mineral fertilizers

The purpose of the research was to assess the phosphate state of agrochernozem in soybean crops using mineral fertilizers. The experimental site was geographically located in the central part of the Krasnoyarsk forest-steppe (N56.430°, E 92.915°) at the field station educational-research-production complex "Borsky" ("UNPK Borsky"). The scheme of the experiment was represented by the following variants: 1) ammophos - AP (20) + Cs (60) - standard (st); 2) ammophos - AP (40) + Cs (60); 3) sulfoammophos - SAP (10) + Cs (60); 4) sulfoammophos - SAP (20) + Cs (60); 5) nitroammophosk - NAPK (10) + Cs (60); 6) nitroammophos - NAPK (20) + Cs (60); 7) phosphorite flour - PF (1 t/ha) + ammonium sulfate - Na (100) + potassium sulphate - Ks (60); 8) phosphorite flour - PF (1.5 t/ha) + ammonium sulphate - Na (100) + potassium sulphate - Ks (60). A deficiency of phosphorus-containing minerals in the studied agrochernozem was revealed. The content of bulk phosphorus indicated a rather high content in the arable layer of all variants of the experiment (0.31 - 0.48 %). A significant proportion of organophosphates in the soil has been suggested. Moderately high inverse dependencies between the rate of phosphorus release (intensity factor) and phosphatase activity on the ratio of Corg:Porg at the beginning of the soybean growing season were found. Phosphatase activity was closely related to phosphorus endowment: the less phosphates available in the soil, the higher the enzyme activity. The assessment of the provision of agrochernozems with mobile phosphorus according to the method of F.V. Chirikov in all variants of the experiment indicated a high level of its content during the entire period of observations. On the contrary, the "intensity factor" data revealed a low level of easily soluble phosphorus compounds in the pre-sowing period (background content). The application of mineral fertilizers was accompanied by the release of phosphates into the soil solution.