Abstract
The off-site effects of agricultural organic soils include the leaching of N, P, and organic carbon (OC) to watercourses and CO2, CH4, and N2O emissions into the atmosphere. The aim of this study was to quantify how the thickness of organic layers affects these loads. A 19.56-ha experimental field drained by subsurface pipes was established in Ruukki, northwestern Finland. Three plots had a 60–80 cm-thick sedge peat layer and three others had a thickness of 20 cm or less. The drainage pipes lie in mineral soil that, in this field, contains sulfidic material. This study documents the experimental settings and reports on the leaching of substances in the first two years, as well as CO2, CH4 and N2O emissions during eight weeks in one summer. Total N (TN) and OC loads were higher from the thicker peat plots. The mean TN loads during a hydrological year were 15.4 and 9.2 kg ha−1 from the thicker and thinner peat plots, respectively, with organic N representing 36% of TN load. Total P (TP) load averaged 0.27 kg ha−1 yr−1. Dissolved P load represented 63 and 36% of TP in the thicker peat area and only 23 and 13% in the thinner peat area, and was thus increased upon peat thickness. These N and P loads through the subsurface drainage system represented roughly 83% of TN and 64% of TP loads from this field. There were no clear differences in greenhouse gas emissions among the plots during the eight-week monitoring period. Slowly oxidizing sulfide in the subsoil resulted in annual leaching of 147 kg S ha−1, almost ten times that of non-sulfidic soils. Our first results emphasize the effect of the peat thickness on the leaching of substances and warn about considering all organic soils as a single group in environmental assessments.
Highlights
The organic soils of cool and humid climates form a major carbon (C) stock (Batjes, 1996; Scharlemann et al, 2014) and commonly serve as farmland (Berglund and Berglund, 2010; Buschmann et al, 2020)
The subsurface drainage pipes of all plots were clearly installed in the mineral soil at least 60 cm below the horizons consisting of organic material
We introduce a 19.6-ha experimental field that was established in 2016 at the Ruukki field station to monitor the leaching of substances and greenhouse gas (GHG) from a cultivated peatland
Summary
The organic soils of cool and humid climates form a major carbon (C) stock (Batjes, 1996; Scharlemann et al, 2014) and commonly serve as farmland (Berglund and Berglund, 2010; Buschmann et al, 2020). Many studies have highlighted the leaching of major nutrients and high greenhouse gas (GHG) emissions from cultivated organic soils (Duxbury and Beverly, 1978; Kasimir-Klemedtsson et al, 1997; Kløve et al, 2010; Tubiello et al, 2016; Regina et al, 2019). According to soil tests carried out in Finland between 1998 and 2002, 13.6%, or 300,000 ha, of agricultural land in the country consisted of organic soils (Myllys and Sinkkonen, 2004), and in the northern half of the country, almost 30% of agricultural land represented organic soils They are mostly used for spring cereal and grass cultivation to provide fodder for dairy production (Kekkonen et al, 2019). There is a need for focused studies to accommodate the environmental challenges related to cultivation and to promote sustainable agricultural production
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