Influence of Fertilizer Systems on the Content of Mobile and Highly Mobile Phosphorus and Potassium in Sod-Podzolic Light Loamy Soil

In a two-factor long-term field experiment in the vetch-oatmeal–winter wheat–barley crop rotation, the effect of fertilizer and liming systems on changes in the content of mobile (according to Kirsanov) and lightly mobile (according to Scofield) phosphorus and potassium in sod-podzolic light loamy soil was studied. The effect of various fertilizer systems was studied: organic (cattle manure), mineral and 2 organomineral fertilizer systems on a limed background and without liming. According to the effect on crop yields, fertilizer systems were arranged in the following ascending order: organic ≥ mineral ≥ organomineral (half doses) > organomineral (full doses). In the 2nd rotation, the aftereffect of liming at a dose of 1.0 А_g at an initial pH_KCl value of 5.1–5.2 units was statistically insignificant. The use of an organomineral fertilizer system (manure at a dose of 50 t/ha + N150P120K225) made it possible to increase the productivity of the crop rotation link to 3.84–4.07 t feeding units (f.u.)/ha, which was 1.57–1.75 t f.u./ha more than in the control without fertilizers. At the same time, the content of mobile phosphorus (capacity factor) increased by 13%, the degree of mobility (intensity factor) increased by 2.6 times compared with the control. The content of mobile potassium increased by 65%, the degree of its mobility increased by 2.0 times. The difference utilization rate was 18–21% P₂O₅ and 41–46% K₂O. The specific phosphorus removal was 9.5–9.9, potassium – 32–33 kg f.u./t and did not depend on the level of soil acidity. The phosphorus balance had a positive average correlation (r = 0.58) with the change in the content of readily available phosphorus determined by the Scofield method. The potassium balance had an average strength correlation (r = 0.46) with a change in the content of mobile potassium determined by the Kirsanov method. We believe that in agrochemical practice, these methods should be used together, mutually complementing each other, most fully characterizing the mobility and availability of phosphorus and potassium in the soil for plants.