Changes in the Content of Organic Carbon and Physicochemical Properties of Soddy-Podzolic Soil and Crop Rotation Productivity as a Result of Long-Term Use of Increasing Rates of Nitrogen Fertilizers under the Conditions of the Cis-Urals

The effect of long-term application of increasing rates of nitrogen fertilizers on changes in the main fertility parameters of soddy-podzolic heavy loamy soil (Albiс Retisol (Abruptic, Aric, Loamic)) has been studied in a stationary experiment established in Perm krai in 1972. The assessment was performed in dynamics in the eight–field crop rotation (I–VI rotations) in the arable layer (0–20 cm) and at the end of the VI rotation in the 0–60 cm layer of the soil profile. The maximum losses of Corg in the arable layer in all studied variants (without fertilizers, P60K60 (background), background + N30–120) were observed 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 Corg in 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 removed in the 1st–5th rotations, and plowed into the soil in the 6th rotation, which affected the developing balance of Corg. An increase in the Corg content in the soil (0–20 cm) was observed at the end of the 6th rotation in the N120P60K60 variant, its amount became close to the initial level. The Corg content at the end of the 6th rotation in the N30–90P60K60 variants was by 16–20% less than the initial level, and the Corg reserves were 6.6–8.1 t/ha smaller. Long–term application of nitrogen fertilizers in the rates of N30–90P60K60 led to a decrease in Corg content in the 20–40 and 40–60 cm soil layers; and no decrease was found in the N120P60K60 variant. A decrease of pHKCl, the degree of soil base saturation, and an increase in hydrolytic acidity has been found at the end of the second rotation as a result of using high rates of nitrogen fertilizers N90–120P60K60, despite liming carried out at the beginning of this rotation. Deterioration in soil acidity began to be observed only from the fourth rotation, when using low rates of N30–60P60K60. The productivity of crop rotation as a result of application of N30–120P60K60 fertilizers increased by 15–20%.