Current forage production on tile drained peat soil is challenged by low drainage efficiencies and large GHG emissions. Peat inversion is a valid alternative where peat less than 1.5 m deep lies on top of self-draining mineral soil. The peat body is covered by the underlying mineral soil while maintaining connectivity to the self-draining subsoil. PEATINVERT builds on findings from the previous DRAINIMP-project. In PEATINVERT we study whole-year-round GHG-emissions and source/sink processes at the same location (Fræna, Møre & Romsdal) in adjacent fields with inverted and tile drained peat. In spring 2017, we established new sites for measuring emissions of N2O and CH4 at the inverted and surface graded peat: an upper site (with 4 plots for emission measurements) near the top of the graded surface and a lower site (4 plots + 3 unfertilized plots) closer to the main ditch separating inverted and tile drained peat. At the upper site, the thickness of the mineral material cover is 80-105 cm, whereas it is 45-55 cm at the lower site. On the tile drained peat we use the same location as in DRAINIMP (4 plots + 3 unfertilized). At the inverted peat site, we periodically measure concentration profiles of N2O, CH4, O2 and CO2 in the soil air at 20 cm depth intervals down to the buried peat. O2 profiles are monitored continuously in both drainage systems using Apogee sensors. Ground water observation wells are installed (two at each location on inverted peat) and water tables (GWT) are registered manually. Soil samples are analysed for texture, pH and content of carbon and nitrogen. At the tile drained peat, GWT is manually observed in three wells. From summer 2017 onwards, GWT was measured continuously in both drainage system with pressure cells. Campaign measurements of ecosystem respiration in both systems were carried out in 2017 and 2018 (spring, 1.cut, 2. cut, autumn) using a CO2 Gas Analyzer (EGM-5, PP Systems) with opaque chambers along with soil temperature and moisture measurements. NDVI and above- and belowground plant biomass were measured simultaneously to infer differences in C fluxes in the two systems. Incubation experiments have been conducted in order to determine the methane oxidation potential in the mineral material covering the inverted peat.
The mineral material cover has a high content of coarse silt and fine sand, and is low in organic matter. GWT in the inverted peat is kept below 20 cm, whereas in the tile drained peat GWT is close to soil surface when precipitation is high. Soil moisture is lower in inverted than in tile drained peat. There is little difference in mean soil temperature, but larger diurnal variations are found in the inverted peat. Measurements in fertilized tile drained peat in 2017 and 2018 showed large cumulative emissions of methane, being 72 and 16 kg/ha CH4-C, respectively. Methane emissions from upper site inverted peat was 0.6 kg/ha CH4-C in both years, whereas it in lower site was 2.1 and 1.5 kg/ha CH4-C in 2017 and 2018, respectively.
In the inverted peat, we found up to 50 vol% CH4 in the soil air close to the buried peat, which strongly decreased towards the soil surface at both inverted sites. Incubation experiments with soil samples from different depths of the mineral cover layer showed a methane oxidation potential between 0.1 and 1.4 mg CH4-C/hg soil at 15°C. The oxidation tended to be higher just above the peat than closer to the soil surface.
Inversion of peat did not decrease emissions of N2O. Cumulative emissions over 159 days in the tile drained peat was 9.8 kg/ha N2O-N in fertilized plots, whereas there was no emission in unfertilized plots. In the inverted peat the emissions in the same period were 8.5; 10.3 and 1.4 kg N/ha in upper, lower and lower unfertilized plots, respectively). Depth profiles of N2O in soil air indicated that N2O is produced in the mineral layer and not in the buried peat. Small emissions in unfertilized plots both in inverted and tile drained peat suggest that N2O emissions are fertilizer induced.
Continuously monitored O2 profiles show O2-concentrations of 0-5 vol% in the top of the buried peat and much higher concentrations (5-20 vol%) in the tile drained peat. In the dry summer of 2018 we measured an O2-concentration of 15 vol% at 55 cm depth in the tile drained peat, whereas in the inverted peat the O2-concentration was never more than 8 vol%. Dark chamber measurements in 2018 showed a CO2-flux of 1.43,1.49 and 2.35 kg/ha/h CO2-C after 1.st cut and 1.4, 1.25 og 2.01 kg/ha/h CO2-C after 2.cut in inverted upper site, inverted lower site and tile drained peat, respectively. The mass of roots was lower at tile drained than inverted peat, which means less autotrophic respiration in tile drained peat. The larger respiration measured at tile drained peat therefore results from a larger heterotrophic respiration because of a larger degradation of organic matter.
Gjennom arbeidet i DRAINIMP og PEATINVERT har ein resultat frå ein forholdsvis lang tidsserie frå 2014 til 2018 med utsleppsmålingar av lystgass og metan i tradisjonelt grøfta, næringsfattig myr. Denne kunnskapen bør nyttast i den norske utsleppsrekneskapen for klimagassar. Kunnskap om effekt av omgraving på utslepp av klimagassar og avling er nyttig for rådgjevarar, forvalting og bønder i forhold til å redusere utsleppet av klimagassar frå jordbruket. Kunnskapen er også nyttig i forhold til å oppnå stabile avlingar i eit framtidig våtare klima der jordbruksdrifta ofte må tilpassast korte onnevindauge der jorda er lagleg for drift.
PEATINVERT aims to increase knowledge about greenhouse gas (GHG) emissions from farmed organic soils in Norway. Current forage production on tile-drained peat soil is challenged by low drainage efficiencies and large GHG emissions. Peat inversion is a valid alternative where peat less than 1.5 m deep lies on top of self-draining mineral soil. The peat body is covered by the underlying mineral soil while maintaining connectivity to the self-draining subsoil. PEATINVERT builds on findings from a previous project (DRAINIMP,NFR no.225274) which found methane(CH4) emissions to be much lower in inverted than in tile-drained peat, and nitrous oxide (N2O) emissions in the same magnitude. PEATINVERT will study whole-year-round GHG-emissions and source/sink processes at the same location (Fræna, Sunnmøre) in adjacent fields with inverted, tile drained and uncultivated peat. To investigate whether peat inversion has a potential to protect peat from degradation, continuous O2 profiles will be monitored in both drainage systems. Discontinuous measurements of CH4 and CO2 in soil air will be used to assess the peats? CH4 production potential. Preliminary measurements suggested that the buried peat produced large amounts of CH4, which were oxidized before reaching the atmosphere. We will quantify CH4 oxidation in more detail by laboratory incubations. To arrive at a more complete GHG balance for forage production on tile-drained and inverted peat, we will estimate the C balance in both drainage systems based on measured ecosystem respiration and above- and belowground plant biomass. Present C stocks in the surface layers of inverted and tiled-drained peat will be quantified and archived. Whole-year-round measurements of N2O emissions will be used to study N2O emission patterns and response to fertilization in inverted and tile-drained peat. We will cooperate with, and actively disseminate our findings to the advisory service, farming community and regional agricultural authorities.