The Content of Various Forms of Potassium in the Soil Profile of the Sod-Podzolic Soil of the Pre-Urals

The effect of long-term use of nitrogen, phosphorus and potash fertilizers and their combinations (N, P, K, NP, NK, PK and NPK) on chang in sod-podzolic heavy loamy soil (Albic Retisol (Abruptic, Aric Loamic)) was studied the content of gross potassium and its easily exchangeable, exchangeable and non-exchangeable compounds. The research was carried out in a meter layer of soil under the conditions of a long-term stationary experiment laid down in the Perm Region in 1978. In the experiment, ammonium nitrate or urea, double or simple superphosphate and potassium chloride were used. The dose of fertilizers was 90 kg/ha in the primary plant food. Long-term application of potassium chloride in pure form and in combination with superphosphate and nitrogen fertilizers (K₉₀, (PK)₉₀, (NK)₉₀, (NPK)₉₀) provided an increase in the gross content of potassium in the arable soil layer by 1.1–1.2 times and its various compounds by 1.1–2.8 times (relative to the control variant). A narrowing of the ratio of non-exchangeable forms of potassium to exchange forms is noted here. Changes in the meter layer of soil depended on the combination of fertilizers, the studied form of potassium compounds in the soil. The introduction of only nitrogen and phosphorus fertilizers (N₉₀, P₉₀, (NP)₉₀) without compensation for potassium removal during five rotations of the eight-field field crop rotation led to a decrease in the reserves of exchangeable and non-exchangeable potassium compounds in the 0–40 cm layer by 15–20%. The minimum level of potassium exchange compounds in sod-podzolic heavy loamy soil in a layer of 0–20 cm was 108–112 mg/kg.