Sizes and Ratios of Organic Carbon Pools in Gray Forest Soil under Long-Term Application of Mineral and Organic Fertilizers

Abstract

Soil organic matter (SOM) is proposed to subdivide into structural and process pools. Structural pools include particulate organic matter (CPOM) and mineral-associated organic matter (CMAOM), and process pools include microbial biomass (Cmic) and potentially mineralizable organic matter (C0). The studies were carried out in a long-term microfield experiment on gray forest soil (Luvic Retic Greyzemic Phaeozems (Loamic)). Mineral (N 90–360, P2O5 75–300 and K2O 100–400 kg/ha) and organic (fresh cattle manure from 25 to 100 t/ha) fertilizers in increasing doses were applied annually for 9 years. The increasing in soil organic carbon (Corg) stocks from NPK and manure was 5–10 and 38–83%, respectively. The application of extreme doses of manure (700 to 900 tons/ha in 9 years) led to saturation of the soil with organic carbon. SOM pools sizes decreased in the sequence CMAOM CPOM C0 Cmic, amounting to 7.91–12 g/kg (50–84% of Corg), 0.76–12 g/kg (8–50%), 0.32–1.71 g/kg (2.8-13.7%) and 0.09-0.56 g/kg (0.8-3.7%), respectively. CPOM pool size depended mainly on the dose of mineral and organic fertilizers, and CMAOM depended on the duration of fertilizer application. Both Cmic and C0 pools increased with the manure dose and decreased with the NPK dose. The long-term manuring did not produce a cumulative accumulation of C0 in the soil. It is emphasized that the separation of structural and process pools can be used for monitoring of SOM quality and functions.