Influence of degree of cultivation of sod-podzolic soil on dynamics of content of soil organic carbon

In 1999–2001 on the fields of the Falenky Breeding Station (Kirov region), the dynamics of the content of soil organic carbon (C org ) and its labile part (C lab ) in sod-podzolic arable soil of varying degrees of cultivation were studied. The arable layer of weakly cultivated variant of the soil was characterized by high acidity (pH KCl – 3.88) and low organic carbon content (C org – 0.91 %). The well cultivated variant had an acidity close to neutral in the arable horizon (pH KCl – 6.14) and a total carbon content at the average level for sod-podzolic loamy soils of the region (C org – 1.10 %). Soil samples were taken during the growing season once a month in a sixfold repetition from the arable horizon and in a threefold repetition for horizons A2B and B. It was revealed that during all years of observation in the arable horizon of the soil of the cultivated variant, the C org content was significantly higher (by 16–76 %). In the underlying horizons of soils of both variants, the carbon content was sharply reduced to 0.2–0.6 %. The content of labile part of organic carbon did not differ by variants and varied from 0.05 to 0.19 % depending on the horizon and observation period. However, in the arable horizon of weakly cultivated soil, the proportion of labile carbon in the composition of total organic carbon was significantly higher, which indicated less stability of the soil organic matter system. The content of both forms of soil organic matter varied significantly over the years and during the growing season. Maximum values of C org content were noted at the beginning and at the end of the observation season. Minimum values were noted in July. Content of C lab was decreasing from the beginning to the end of the season.