Loss of organic carbon in erosion and as dissolved organic carbon from agricultural soil

Ms Noora Manninen1, Ms Sanna Kanerva1, Ms Riitta Lemola2, Ms Eila Turtola2, Ms Helena Soinne3

1University Of Helsinki, Helsinki, Finland, 2Natural Research Institute Finland, Jokioinen, Finland, 3Natural Research Institute Finland, Helsinki, Finland

The loss of organic carbon (OC) weakens soil structure and increases the risk of erosion, thus decreasing soil productivity and the quality of surrounding waters. Water can transport OC from agricultural soils as dissolved organic carbon (DOC) or as attached to erosion material. A global decline in agricultural soil OC content has been suggested to result from intensive land management within the past decades. In addition to enhanced soil organic matter mineralization, tillage increases the risk of erosion by weakening soil structural stability, and thus, is likely to increase the loss of soil OC. However, agricultural managements that increase topsoil OC content may increase the annual DOC loads. The aims of this research were to quantify discharge-transported OC loads from agricultural land in Boreal zone, and to study the effects of soil managements on OC loss. We collected discharge samples from surface runoff and subsurface drainage for two years (2015-2017) on two clay soil sites in Finland. The studied agricultural managements were plough, no-tillage, mineral and manure fertilization, and permanent grassland. Annual discharge-exported total OC loads from cultivated plots were 20–70 kg ha-1 and from permanent grassland 50–80 kg ha-1. The share of DOC load was dominant (67–96% for cultivated plots and 90% for grassland plots) compared to erosion-transported OC load. Annual precipitation varied substantially between the years, thus effecting the loads. Total OC loads were higher from ploughed soil compared to no-tillage management only on the first year. Further, the OC loads did not differ between mineral and manure fertilization. The total OC loads in subsurface drainage were higher than in surface runoff when soil was ploughed. Topsoil (0-5 cm) OC% correlated negatively with erosion-transported OC load and positively with DOC load, when cumulative discharge volume was considered typical.

Biography: In my PhD thesis I´m studying the loss of organic carbon (OC) in discharge water from agricultural Boreal soils. We study the chemical characteristics of soil OC under different agricultural managements, the OC loads transported by discharge water, and the impacts of OC loss on soil productivity and water quality.

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