Evaluation of Soil Organic Carbon Stability in Different Land Uses in Lithuania

The effective management of soil organic carbon (SOC) is highlighted as one of the strategies and cost-effective options for mitigating climate change, while soil nitrogen (N) often is specified as an essential element for plant growth. This study was conducted to evaluate basic soil physical, chemical, and microbial indicators in three major soil types dominated in Lithuania—Arenosols, Retisols, and Cambisols—under forest land, perennial grassland, and arable land. Furthermore, soil microbial biomass carbon (SMBC) and nitrogen (SMBN), their ratio, and soil microbial respiration (microbial CO2) next to SOC and total N were hypothesized to be important measures for assessing SOC stability under different land uses. Therefore, selected soil indicators were evaluated in the surface 0–10 and 10–20 cm mineral soil layers. The study results showed higher concentrations of SOC, N, SMBC, and SMBN, and soil microbial CO2 in forest land and perennial grasslands than in arable land. The higher SMBC/SOC and SNBN/TN ratios indicated a higher ability to accumulate SOC and N in forest land and grasslands. Higher SOC immobilization in forest land and higher N immobilization in arable land were both specified by the obtained SMBC:SMBN ratio. This study identified forest land followed by grassland as the best land management practice that addresses soil C sequestration through higher C immobilisation. Assessing soil in forest land as a control land use next to the agricultural land could be a reasonable soil management practice to evaluate C sequestration in the region. Additionally, it was assumed that evaluation of the SMBC and SMBN concentrations together with soil physical and chemical indicators allow for a more effective assessment of SOC stability. Taken together, these findings support recommendation to develop grassland (and especially forest land systems) through afforestation or within agroforestry system, without reducing the importance of the agricultural sector.