Armolaitis, K., Aleinikovienė, J., Baniūnienė, A., Lubytė, J. and Žėkaitė, V. 2007. Carbon Sequestration and Nitrogen Status in Arenosols Following Afforestation or Following Abandonment of Arable Land. Baltic Forestry 13 (2): 169-178

Over 600 000 ha of agricultural land on infertile soils (mainly Arenosols) are or soon will be abandoned in Lithuania. According to the resolution of the Kyoto Protocol, afforestation of this land could be relevant with the focus on carbon sequestration. The current study was carried out in a long-term permanent experiment in which arable Haplic Arenosols were afforested or before the abandonment were used as arable land during 25-year-long period. Soil chemical changes with an emphasis on organic carbon (C) and total nitrogen (N) pools, and the storages in ground vegetation cover and the roots were compared in 45-year-old Scots pine (Pinus sylvestris L.) plantations and abandoned (11 years ago) arable land. The former plaggic Ap horizon was less acid (by 1.3-1.9 pHCaCl2 units) and 2-3 times more saturated with mobile phosphorus and potassium compounds in plots on formerly fertilized abandoned arable land than in afforested with pine plantation plots. The total C pool at 100 cm mineral soil depth (including O horizons) in abandoned arable land (3.81 kg C m-2) was 1.7 times less than in pine plantations (6.52 kg C m-2), mainly because of C accumulation in the forest floor (2.24 kg C m-2). The differences in mineral horizons were not significant, although the root mass in mineral topsoil was more than 10 times larger in pine plantations, except the surface 0-2 cm layer of the former Ap horizon in which the C pool was 3 times larger in pine plantations (0.72 kg C m-2) than in abandoned arable land (0.22 kg C m-2). Total soil N pools were at the same level (0.47-0.54 kg N m-2) because the mineral soil to the depth of 100 cm contained 90% and more of N in both the abandoned arable land and the pine plantations. It was concluded that pine plantations better preserve C and N pools in mineral horizons of Haplic Arenosols, than abandoned arable land that was formerly intensively fertilized with conventional NPK fertilizers and farmyard manure as well.

Key words:Lithuania, Haplic Arenosols, abandoned arable land, afforestation, Scots pine, Pinus sylvestris, ground vegetation, roots, soil organic carbon, total nitrogen