The effect of long-term application of increasing doses of nitrogen fertilizers on changes in the main fertility parameters of sod-podzolic heavy loamy soil (Albiс Retisol (Abruptic, Aric, Loamic)) was studied in a stationary experiment established in the Perm Territory in 1972. The assessment was performed in dynamics by rotations of the eight–field crop rotation (I–VI rotations) in the arable layer (0–20 cm) and at the end of the VI rotation along the profile in the 0–60 cm layer. The maximum losses of Corg content in the arable layer in all studied variants (without fertilizers, P60K60 (background), background + N30–120) were noted in the first rotation from 1.41–1.60 (initial level) to 1.12–1.22% (by 15–30%). No reliable further decrease in the amount of C in the soil (0–20 cm) was observed in the following rotations with the application of nitrogen fertilizers. The straw of grain crops in the experiment was alienated in the 1st–5th rotations, and plowed under in the 6th rotation, which affected the developing balance of C. An increase in the C content in the soil (0–20 cm) was noted at the end of the 6th rotation in the N120P60K60 variant, its amount became Close to the initial level. The C org content at the end of the 6th rotation in the N30–90P60K60 variants was 16–20% less than the initial level, and the Corg reserves were 6.6–8.1 t/ha. Long– term application of nitrogen fertilizers at doses of N30–90P60K60 led to a decrease in the C content in the 20–40 and 40–60 cm soil layers; no decrease was found in the N120P60K60 variant. A decrease in the pHKCl index, the degree of soil saturation with bases, and an increase in hydrolytic acidity were noted at the end of the second rotation as a result of using high doses of nitrogen fertilizers N90–120P60K60, despite the liming carried out at the beginning of this rotation. Deterioration in soil acidity began to be observed only with the fourth rotation when using low doses of N30–60P60K60. The productivity of crop rotation as a result of using N30–120P60K60 fertilizers increased by 15–20%.
М. Т. Vasbieva (Wed,) studied this question.