Effect of Long-Term Application of Organic and Mineral Fertilizers on the Organic Carbon Content and Nitrogen Regime of Soddy-Podzolic Soil

The effect of long-term application of organic and mineral fertilizers on the organic carbon content and nitrogen regime of soddy-podzolic heavy loamy soils (Umbric Albeluvisols Abruptic) was studied in a long-term stationary experiment established in Perm region in 1976. Long-term crop growing (for about 40 years) resulted in the decrease of organic carbon content from 1.28 to 1.13%. The application of cattle manure at the rate of 40 t/ha and mineral fertilizers NRK (I rotation-N120P120K120, II rotation-N90P90K90, III-V rotations-N60P60K60) slowed down the process of organic matter mineralization but did not completely compensate for the organic carbon loss. The application of sewage sludge at the rate of 40 t/ha once in the seven-field crop rotation allowed maintaining the organic carbon content in the soil at the initial level. To assess the composition of soil nitrogen, acid hydrolysis was used. The application of manure reliably increased the contents of difficultly hydrolyzable, hydrolyzable, and mineral fractions of nitrogen in the soil by 1.1-1.4 times Prolonged use of sewage sludge significantly increased (by 1.1-1.6 times) the content of total nitrogen and all its fractions in the soil. The application of mineral fertilizers contributed to an increase in the contents of total, easily hydrolyzable, and mineral nitrogen by 1.1-1.4 times. The maximum positive effect on the organic carbon content and the nitrogen regime was observed in the case of prolonged use of organic fertilizers against the background application of mineral fertilizers. The relative content of nitrogen fractions in the soil remained fairly stable and indicated the stability of nitrogen pool in the soil over time.