Features of the Humus Status of Gray Forest Soil Depending on Slope Aspect and Steepness

The humus status of gray forest soil formed on loesslike loams on the northern and southern slopes of 1°, 3°, and 5° in the Central Chernozem Region was studied. Soil samples were taken in pits from the middle part of the Aplow, A1, A1A2, and B horizon in three replications. We determined the organic carbon and the fractional group composition of humus according to the scheme by I.V. Tyurin modified by V.V. Ponomareva and T.A. Plotnikova. The content of mobile humus substances was analyzed in 0.1n NaOH extract from soil without decalcification by the approach modified at the V.V. Dokuchaev Soil Science Institute with preliminary composting. Gross nitrogen was determined by the wet ignition method according to Ginzburg with ammonia distillation according to Kjeldahl. It was found that the content of organic carbon in gray forest soil was higher on the northern slope than on the southern one. Mineralization of organic matter was faster in soil of the southern slope, which was related to the narrower C : N ratio as compared to the soil of the northern slope. It was revealed that the mobility of humus substances in gray forest soil more strongly depended on the slope aspect than on its steepness. The ratio between organic matter components in the studied soils was determined by agroecological conditions; therefore, the qualitative and quantitative composition of organic matter should be regulated, taking them into account.