Impact of sward formation on soil organic carbon variation and relations with soil microbial activity

The aim of the study was to estimate the impact of temporal sward formation on soil organic carbon (SOC) variation and soil microbial biomass carbon (MBC) content in rhizosphere. The soil of experimental sites was Bathygleyic Dystric Glossic Retisol , where the soil acidity (pH) was 3.9 and 5.0, and four mixtures of legumes and grasses were cultivated. The mixtures were composed of one legume variety and two grass varieties – timothy ( Phleum pratense L.) 35% and meadow grass ( Poa pratensis L.) 15%, 50% of each: 1) red clover ( Trifolium pratense L.), 2) white clover ( Trifolium repens L.), 3) hybrid clover ( Trifolium hybridum L.), and 4) alfalfa ( Medicago sativa L.). In the soil of different swards, SOC was more accumulated at 0–10 cm depth. The species composition of the sward did not have any significant influence on the studied indicators. In the soil of swards with pH 5.0, the SOC content in three years increased by 3.3%, SOC stock by 8.5%, and the C to N ratio was favourable for the SOC accumulation. In the naturally acidic soil (pH 3.9), the SOC content and SOC stock decreased by 12.0% and 3.3%, respectively. In the 4th year of sward formation, irrespective of the soil acidity, the SOC stock decreased, but it was similar as in the beginning of sward formation. Sward formation had a significant impact on the soil MBC. In the 2nd year of sward formation, the MBC content increased by 1.7 times in the soil with pH 5.0 and by 2 times in the naturally acidic soil compared to the year of sowing and remained relatively stable in the 3rd and the 4th year of sward formation irrespective of the soil acidity.