Contribution of water erosion to organic carbon and total nitrogen loads in agricultural discharge from boreal mineral soils

Noora Manninen; Sanna Kanerva; Riitta Lemola; Eila Turtola; Helena Soinne

doi:10.1016/j.scitotenv.2023.167300

Contribution of water erosion to organic carbon and total nitrogen loads in agricultural discharge from boreal mineral soils

Sci Total Environ. 2023 Dec 20:905:167300. doi: 10.1016/j.scitotenv.2023.167300. Epub 2023 Sep 22.

Authors

Noora Manninen¹, Sanna Kanerva², Riitta Lemola³, Eila Turtola³, Helena Soinne⁴

Affiliations

¹ University of Helsinki, Department of Agricultural Sciences, Unit of Environmental Soil Science, Viikinkaari 9, P.O. Box 56, FI-00014 Helsinki, Finland. Electronic address: noora.manninen@helsinki.fi.
² University of Helsinki, Department of Agricultural Sciences, Unit of Environmental Soil Science, Viikinkaari 9, P.O. Box 56, FI-00014 Helsinki, Finland.
³ Natural Resources Institute Finland, Tietotie 4, FI-31600 Jokioinen, Finland.
⁴ Natural Resources Institute Finland, Latokartanonkaari 9, FI-00790 Helsinki, Finland.

PMID: 37742969
DOI: 10.1016/j.scitotenv.2023.167300

Abstract

While organic carbon (OC) in agricultural mineral soils is widely studied in terms of soil carbon sequestration and gaseous emissions, discharge-induced OC loss from soil is still poorly understood and estimations of boreal soil OC loads within water erosion are lacking. Loss of organic matter from arable soils is a concern for surface water quality, climate change and soil productivity. The main aim of this study was to quantify the role of water erosion in total OC and nitrogen (N) loads exported in agricultural discharge from boreal mineral soils under various cultivation practices. Surface water and subsurface drainage were collected near-continually over 2 years in two clayey and one sandy soil in Finland. Eroded sediment was mechanically separated by centrifugation from all discharge samples to detect sediment OC% and N% by dry-combustion method. Dissolved OC and N concentrations in selected discharge samples were measured with high-temperature catalytic oxidation of unfiltered supernatant. A multiple linear regression model was used to study the significant factors affecting dissolved, sediment and total OC loads. In the clayey soils, the sediment OC (2-24 kg ha^-1 y^-1) and N (0.2-1.1 kg ha^-1 y^-1) export accounted for up to 35 % and 20 % of the annual discharge-induced total loads of OC (19-85 kg ha^-1) and N (2-8 kg ha^-1), respectively. In the sandy soil, erosion was negligible and dissolved loads of 17-35 kg OC ha^-1 y^-1and 4-7 kg N ha^-1 y^-1 were detected. Subsurface drainage exported most of the sediment-associated OC and N loads from clayey soils. For the total OC loads, the distribution varied between the discharge routes, while the total N loads were mostly exported in subsurface drainage in both soil types. Sediment OC and N exports were related to soil plowing and discharge intensity, while dissolved OC loss was promoted by high surface soil OC%. Our results also indicated that a single cultivation practice may affect sediment and dissolved loads in opposite ways. These findings can be used to complement carbon budget estimations for mineral agricultural soils, and to assess soil management effects on terrestrial organic matter loading to boreal surface waters.

Keywords: Carbon budget; Cultivation practices; Dissolved loads; Sediment loads; Subsurface drainage; Surface runoff.