Changes in the Potassium Regime of Soddy-Podzolic Heavy Loamy Soil During Long-Term Extensive Cultivation of Agricultural Crops and the Use of Fertilizers

The change in the gross content of potassium its easily mobile (extract 0.01 M CaCl₂), mobile (according to Kirsanov) and non-exchangeable (according to Gedroits) compounds in a meter-long layer of soddy-podzolic heavy loamy soil (Albiс Retisol (Abruptic, Aric, Loamic)) during long-term extensive cultivation was studied crops and fertilizer application. The studies were carried out in a long-term stationary experiment established in 1968 in the Perm region. We experimentally studied organic (cattle manure), mineral and organomineral fertilizer systems, leveled by nutrients (control – without fertilizers, manure 10 and 20 t/ha per year, NPK equivalent to 10 and 20 t of manure, manure 5, 10 and 20 t/ ha + NPK equivalent to manure). Eight-field fallow-grain-row crop rotation. An assessment of changes in the potassium regime of arable soil was carried out in comparison with a virgin analogue (grass-forb meadow). It was established that long-term cultivation of agricultural crops (almost 50 years) without the use of fertilizers led to a decrease in the gross reserves of potassium (by 13%), its mobile compounds (by 43%) in the 0–20 cm layer, and the reserves of easily mobile compounds (by 40%) in a meter layer. The saturation of arable land with fertilizers and the type of fertilizer system influenced the direction of changes in the potassium regime of the soil. The accumulation of easily mobile, mobile and non-exchangeable potassium compounds as a result of long-term use of fertilizers was noted maximum in the 0–40 cm layer; in deeper layers (40–100 cm), on the contrary, a tendency was observed to decrease the content of these forms of potassium (relative to the option without fertilizers). Maintenance of gross potassium reserves in the soil in a layer of 0–20 cm at the level of the virgin analogue (46 t/ha) was noted when using an organomineral fertilizer system with a manure saturation of 10 t/ha per year + NPK equivalent to manure, an increase in reserves to 49 t/ha with manure saturation 20 t/ha per year + NPK equivalent to manure.