Abstract

6219 - 1213

The impact of water erosion on the organic carbon export from agricultural soil

C3.2.4 - Nutrient and contaminant transport in drained soils

Manninen Noora1; Kanerva Sanna1; Lemola Riitta2; Turtola Eila2; Soinne Helena1

University of Helsinki1; Natural Resources Institute Finland2

Soil management, discharge, erosion, organic carbon

The impact of water erosion on the organic carbon export from agricultural soil

Manninen Noora1; Kanerva Sanna1; Lemola Riitta2; Turtola Eila2; Soinne Helena1

University of Helsinki1; Natural Resources Institute Finland2

A declining trend in soil organic matter on Finnish agricultural lands has been discovered within the past few decades. Organic carbon (OC) is transported from soil by discharge as dissolved organic carbon (DOC) and as OC attached onto eroded soil material. The loss of OC weakens soil structure and further increases the risk of erosion. Soil tillage e.g. ploughing increases the amount of eroded material and OC in the discharge. Further, soil managements that increase the topsoil OC content may increase the annual DOC load in the discharge, but the relation between soil OC% and the annual erosion-transported OC load is not clear. Global estimates suggest that 1.9 Pg of terrestrial carbon is transported into inland waters annually. Organic carbon is an important energy source for heterotrophs, and hence it may enhance eutrophication in the receiving waters. The aims of this research are to quantify OC load transported by water erosion from agricultural field, and to study the effects of soil management on OC loss. The discharge water samples were collected during autumn and spring flows in 2015-2017 on two experimental fields on clay soil in Southern Finland (Kotkanoja and Yöni). Surface runoff and subsurface drainage were collected separately from Kotkanoja field, but from Yöni the combined discharge of both routes was collected. At Kotkanoja field, the cultivated plots had conventional ploughing and no-till managements. Yöni field had both mineral fertilization (conventional farming) and manure fertilization (organic farming), in addition to permanent grassland. The preliminary results suggest that the average annual OC loads carried by erosion material from the studied clay soil fields were c. 2-30 kg ha-1. At Kotkanoja field, the loads from ploughed soil were clearly higher compared to no-till plots, as they were in subsurface drainage compared to surface runoff. At Yöni field, there was no clear trend in the erosion-transported OC load between conventional and organic farming, but the loads from grassland were lower compared to these two managements. The OC content in the erosion material from all plots was on average 3% (range 1-8%). Topsoil (0-5 cm) OC% correlated negatively with the erosion-transported OC load in the discharges of both Kotkanoja and Yöni fields.

Keywords: Soil management, discharge, erosion, organic carbon

Financial Support: Nessling Foundation (no. 201500181, 201600017, 201700122), Marjatta & Eino Kolli Foundation (no. 1093), Oiva Kuusisto Foundation (2016 and 2017).

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