Alexander G. Molchanov’s research while affiliated with Russian Academy of Sciences and other places

Haylands are the mildest option for the agricultural use of drained peatlands in terms of CO2 emissions. However, CO2 fluxes and their balance may depend on various conditions including the frequency of mowing and amount of phytomass removed. Based on field measurements of CO2 fluxes using the chamber method and monitoring of environmental factors conducted in 2018–2020 on hayland and fallow on drained peatland in central European Russia, a mathematical model of CO2 balance was built. Numerical experiments showed that mowing of hayland, irrespective of the intensity, did not lead to an increase in CO2 emissions compared to fallow. Fallow and hayland after single mowing had closely modelled net ecosystem exchange (NEE) values: 9.9 ± 2.4 and 8.5 ± 2.7 t C ha⁻¹ season⁻¹, respectively. Furthermore, a single mowing turned out 2.8 t ha⁻¹ of hay (0.8 ± 0.1 t C ha⁻¹), and 4.4 (1.4 ± 0.1) after double mowing. The modelled NEE after double mowing increased to 9.4 ± 2.9 t C ha⁻¹ season⁻¹. A single mowing session in early summer is recommended. Compared to other uses, e.g. arable land, mowing on hayland is a compromise between reducing CO2 emissions and gaining economic benefits from drained peatlands.

The data of episodic field measurements of carbon dioxide balance components (soil respiration — Rsoil, ecosystem respiration — Reco, net ecosystem exchange — NEE) of hayfields under use and abandoned one are interpreted by modelling. The field measurements were carried within five field campaigns in 2018 and 2019 on the drained part of the Dubna Peatland in Taldom District, Moscow Oblast, Russia. The territory is within humid continental climate zone. Peatland drainage was done out for milled peat extraction. After extraction was stopped, the residual peat deposit (1-1.5 m) was ploughed and grassed (Poa pratensis L.) for hay production. The current ground water level (GWL) varies from 0.3-0.5 m below the surface during wet and up to 1.0 m during dry periods. Daily dynamics of CO2 fluxes was measured using dynamic chamber method in 2018 (August) and 2019 (May, June, August) for abandoned ditch spacing only with sanitary mowing once in 5 years and the ditch spacing with annual mowing. NEE and Reco were measured on the sites with original vegetation, and Rsoil — after vegetation removal. To model a seasonal dynamics of NEE, the dependence of its components (Reco, Rsoil, and Gross ecosystem-atmosphere exchange of carbon dioxide — GEE) from soil and air temperature, GWL, photosynthetically active radiation, underground and aboveground plant biomass were used. The parametrization of the models has been carried out considering the stability of coefficients estimated by the Bootstrap method. R2 (α=0.05) between simulated and measured Reco was 0.44 (p<0.0003) on abandoned and 0.59 (p<0.04) on under use hayfield, and GEE was 0.57 (p<0.0002) and 0.77 (p<0.00001), respectively. Numerical experiments were carried out to assess the influence of different haymaking regime on NEE. It was found that NEE for the season (May 15–September 30) did not differ much between the hayfield without mowing (4.5±1.0 tC ha-1 season-1) and the abandoned one (6.2±1.4). Single mowing during the season leads to increase of NEE up to 6.5±0.9, and double mowing — up to 7.5±1.4 tC ha-1 season-1. This means increase of carbon losses and CO2 emission into the atmosphere. Carbon loss on hayfield for both single and double mowing scenario was comparable with abandoned hayfield. The value of removed phytomass for single and double mowing was 0.8±0.1 tC ha-1 season-1 and 1.4±0.1 (45% carbon content in dry phytomass) or 3.0 and 4.4 t ha-1 season-1 of hay (17% moisture content). In comparison with the fallow, the removal of biomass of 0.8±0.1 at single and 1.4±0.1 tC ha-1 season-1 double mowing is accompanied by an increase in carbon loss due to CO2 emissions, i.e., the growth of NEE by 0.3±0.1 and 1.3±0.6 tC ha-1 season-1, respectively. This corresponds to the growth of NEE for each ton of withdrawn phytomass per hectare of 0.4±0.2 tС ha-1 season-1 at single mowing, and 0.9±0.7 tС ha-1 season-1 at double mowing. Therefore, single mowing is more justified in terms of carbon loss than double mowing. Extensive mowing does not increase CO2 emissions into the atmosphere and allows, in addition, to “replace” part of the carbon loss by agricultural production.

It was compared CO2 fluxes measured in 2018 and 2019 on the hayfield at different times after mowing and on the fallow on drained peat soils in the Moscow Oblast. Immediately after mowing in 2019, the ecosystem respiration (Reco) and gross exchange ecosystem of CO2 (GEE) on hayfield decreased 2-fold to 26 and –18 g CO2/m2/day, respectively, and specific GEE (per aboveground biomass) increased 2-fold to 0.56 g CO2/m2/day/ggrass. The Reco and GEE on the fallow in 2019 were 50 and –45 g CO2/m2/day. In 2018, a month after mowing, Reco and GEE on the hayfield (69 and –32 g CO2/m2/day) and on the fallow (66 and –34 g CO2/m2/day) practically did not differ, although the phytomass was different: aboveground – 138 and 368 g CO2/m2, and belowground – 1223 and 600 g CO2/m2. A month after mowing in 2018, the net ecosystem exchange of CO2 (NEE) on the hayfield and on the fallow did not differ and amounted to 38 and 39 g CO2/m2/day. Taking into account the phytomass removed by mowing, the total for the season NEE on the hayfield is shifted towards the assimilation of CO2 in comparison with the fallow.