Evaluation of Soil Organic Carbon Changes on Key Monitoring Sites

Abstract Monitoring of soil organic carbon (SOC) is a part of the Partial Monitoring system – Soil (ČM S-P). ČM S-P consists of two subsystems. One of them is a subsystem of the key monitoring sites (16) in sampling repetition every year. The key monitoring localities cover all soil types, soil use (cropland, grassland) and a wide range of altitudes (111 – 975 m). In 16 key monitoring localities the content of SOC in topsoil is measured every year. This article shows the development of SOC content for a 30-year period on all key monitoring sites, separately on cropland, grassland and sites with land use changes, in lowland (< 300 m) and mountain soils (> 300 m). The 30-year monitoring period was divided into three time periods. On all key monitoring localities, separately on grassland and cropland and on lowland and mountain soils, the lowest median SOC content in the first time period was found. The reason could be substantial changes in Slovakia´s agriculture, mainly a sharp drop in organic fertiliser consumption on 90-ties. Between the first and second time period, SOC content is statistically significantly increased. We assume that it was caused by the state subsidy policy to increase the content of organic matter in the soil. Between the second and the third time period, changes of SOC content were negligible. Our results also show that the main driving forces affecting SOC content are altitude (statistically significantly higher SOC content on mountain soils compared to lowland), land use and land use changes (statistically significant higher SOC content on grassland compared to cropland).