Carbon accumulation and humification in soils of abandoned former agricultural lands in the hemiboreal zone

Abandonment of the agricultural land is a common, topical problem in many post-soviet countries, including Latvia. These changes impact nutrient cycling, soil properties. The results of the study of abandoned agricultural lands in the hemiboreal zone in Latvia validated the theory that after afforestation, in long term, soil accumulates organic carbon (Corg). During the first 30 years of abandonment, Corg content in mineral topsoil does not present a significant increase; it varies from 42 to 43 t haE-1. More rapid Corg content increase was observed in the territories where the age of the forest land had exceeded 30 years; the mean Corg content in 31-60 years old forest stands reached 51.3 t haE-1. The Corg content which has been accumulated in litter increases in older forest sites. In spruce and mixed forest stands, where age of the forest had exceeded 60 years, the mean Corg content in litter was 17.8 t haE-1. Afforestation also changes the content of humic substances and the humification rate in the mineral topsoil. In agricultural lands C of humic substances (Chs ) constituted 65% of total topsoil Corg. In sites where age of the forest land was more than 30 years Chs exceeded 75% of total Corg amount.