Changes in Soil Organic Carbon Stocks and Chemical Properties in Organogenic Soils Under Long‐Term Agricultural Use in Central Europe, Poland

ABSTRACT Organic soils, particularly peatlands, are important carbon sinks. In Europe, almost half of the area has been drained mainly for agriculture, which causes problems with high carbon dioxide emissions. In Poland, peatlands are drained in 86% of the area, and most of them are used as grasslands. The aim of the study was to analyze changes in agriculturally used organogenic soils between 1975 and 2017 using data from 476 reference soil profiles. The results showed a significant decrease in organic soils (≥ 12% SOC), with an increase in percentage organo‐mineral and mineral soils (< 12% SOC). The depth of SOC‐rich layers also decreased significantly and was accompanied by an increase in shallow soils (21–50 cm). The average SOC stock loss was almost 273 Mg C·ha −1 (from 500.4 Mg C·ha −1 to 228.0 Mg C·ha −1 ), with the median being four times lower, and it was observed in 64% of sites. The most significant decrease in SOC stock, by 64.7% compared to 1975, occurred in organic soils (from 762.2 Mg C·ha −1 to 269.3 Mg C·ha −1 ). Our analyses show that with increasing degradation of organic soils, factors that influence carbon content in soil change. In general, after 50 years, for organic soils, drainage was important, while for organo‐mineral and mineral soils, chemical properties, especially nutrient availability, were crucial. Carbon loss was most evident in the driest region of the country. The results indicate that continuous grassland use on organic soils does not offset SOC losses caused by drainage. At the same time, in organo‐mineral and mineral soils, a restraint of SOC stock loss was observed. This suggests that over 50 years of agricultural use of organogenic soils (mainly peat) along with their transformation, a balance between carbon output and input has been established. Considering this, it is an urgent task to update the area covered by organic soils used for agriculture, as it is important for reliable emission reporting and setting goals of organic soil protection and restoration.