Cultivated Peat Soils Research Articles

Mitigation of Greenhouse Gas Emissions by Optimizing Groundwater Level in Boreal Cultivated Peatland

Optimizing the level of groundwater presents a viable strategy for mitigating the greenhouse gas (GHG) emissions associated with the cultivation of peatlands. This study investigated the impact of soil hydrological conditions on carbon dioxide (CO2) and methane (CH4) emissions. The CO2 and CH4 emissions from bare soil were continuously measured using an automated chamber system throughout the growing seasons from 2021 to 2023 at a boreal cultivated peat soil site. Annual CO2 emissions from soil respiration averaged to 21,600 kg ha-1 (April-November) corresponding to carbon (C) loss of 5890 kg ha-1. The CO2 emissions were highly temperature dependent. Lowering the groundwater level (GWL) was found to increase the CO2 emissions nearly linearly. The soil functioned as a CH4 sink for the majority of the growing season, and the total sink corresponded to 27 and 20 kg ha-1 yr-1 CO2 equivalent in 2022 and 2023, respectively. The CH4 emissions occurred generally when soil water content (SWC) exceeded 0.6 m3 m-3 and when GWL was at the depth of less than 30 cm from soil surface. For optimal climate efficiency the mitigation measures must be implemented during the mid-growing season, and the water table should be brought close to the soil surface. Potentially, this can hamper the operation of machinery on the field and reduce the harvested yield. Thus, comprehensive cost-benefit analysis is necessary before adopting a raised water table level in large-scale crop production.

Phosphorus - A key element determining nitrous oxide emissions from boreal cultivated peat soil

Spatial variation in the emission rates of nitrous oxide (N2O) and methane (CH4) in soils can be significant due to the diverse biological, chemical, and physical conditions that influence the production and consumption of these gases. Drained organic soils are known to be hotspots for N2O emissions, and in wet conditions they can also emit CH4. We measured N2O and CH4 fluxes during the winter and growing season at 28 locations across a 7-ha area of drained organic agricultural soil in Eastern Finland. Our findings revealed expected high spatial and temporal variations in emission rates. The measured N2O emissions varied between −0.003 and 30.4 mg N2O m−2 h−1, averaging at 0.94 ± 3.00 mg N2O m−2 h−1 and CH4 emissions varied between −0.27 and 2.90 mg CH4 m−2 h−1, averaging at 0.10 ± 0.33 mg CH4 m−2 h−1. Phosphorus concentration was identified as a limiting factor and a critical determinant of spatial variations in N2O emissions, whereas CH4 emissions exhibited a decreasing trend with increasing sulphur and nitrate concentrations. Our study shows that N2O and CH4 fluxes are linked to other elemental cycles, making it critical to identify key nutrient-related processes that govern the spatial and temporal variability in emissions of these gases.

Minor effects of no-till treatment on GHG emissions of boreal cultivated peat soil

AbstractThe greenhouse gas (GHG) emissions of spring cereal monoculture under long-term conventional tillage (CT) and no-till (NT) treatment established in 2018 were measured in a peatland in Southwestern Finland during the period 2018–2021. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes were measured with chambers approximately every two weeks throughout the period under study. Net ecosystem exchange was measured during the growing seasons, and hourly ecosystem respiration (ER) and gross photosynthesis (GP) were modelled with empirical models. Across the whole period, annual emissions were 6.8 ± 1.2 and 5.7 ± 1.2 Mg CO2–C ha −1 yr−1 (net ecosystem carbon balance), 8.8 ± 2.0 and 7.1 ± 2.0 kg N2O–N ha−1 yr−1, and − 0.43 ± 0.31 and − 0.40 ± 0.31 kg CH4-C ha−1 yr−1 for CT and NT, respectively. The global warming potential was lower in NT (p = 0.045), and it ranged from 26 to 34 Mg CO2 eq. ha−1 yr−1 in CT and from 19 to 31 Mg CO2 eq. ha−1 yr−1 in NT. The management effect on the rates of single GHGs was not consistent over the years. Higher GP was found in CT in 2019 and in NT in 2020. Differences in ER between treatments occurred mostly outside the growing season, especially after ploughing, but the annual rates did not differ statistically. NT reduced the N2O emissions by 31% compared to CT in 2020 (p = 0.044) while there were no differences between the treatments in other years. The results indicate that NT may have potential to reduce slightly CO2 and N2O emissions from cultivated peat soil, but the results originate from the first three years after a management change from CT to NT, and there is still a lack of long-term results on NT on cultivated peat soils.

Industry-driven mitigation measures can reduce GHG emissions of palm oil

Tropical peatland stores a large amount of carbon. In the last 20 years, drainage of Asian peat soil has increased to satisfy the demand of land for plantation agricultures. Industrial oil palm plantations occupy large areas of peatland in Indonesia and Malaysia, with associated GHG emissions and biodiversity loss, here referred to as nature occupation impact. This study performs a detailed Life Cycle Assessment (LCA) of 1 kg of palm oil for two case studies: PT SMART's Hanau and Sungai Rungau facilities in Central Kalimantan, Indonesia. The objective is to quantify the reduction in GHG emissions and nature occupation that has been achieved by implementing the following industry-driven measures: reducing the area of cultivated peat soil, reducing the peat drainage depth, and setting aside part of the land-bank for nature conservation. The results show that 1 kg of palm oil causes 2.72 and 2.25 kg CO 2 -eq./kg palm oil from Hanau and Sungai Rungau facilities respectively. These are 20%–34% lower than average RSPO certified palm oil and 49%–58% lower than average non-certified palm oil. Sungai Rungau achieves the reduction mainly due to a completely peat soil-free supply base. Hanau's peat emissions are instead 0.28 kg, compared to the 0.77 and 2.36 kg CO 2 -eq for RSPO certified and non-certified palm oil respectively, due to a very low drainage depth (18–25 cm compared to 57–73 cm in average of RSPO certified and non-certified respectively) and an overall lower share of oil palms on peat land. The impact on nature occupation is 24%–43% lower in Hanau and Sungai Rungau compared to non-certified oil and 4%–29% lower compared to RPSO certified respectively. About 8% of the total land bank of the Hanau supply-base has been set aside for nature conservation, reducing GHG emissions by 2% and nature occupation by 9%. Both Hanau and Sungai Rungau could also significantly reduce GHG emissions in the palm oil milling stage, by implementing biogas capture in palm oil mill effluent (POME) treatment. • Avoiding the cultivation of peat soil reduces the GHG emissions of palm oil production. • When oil palms are on peat soil, reducing the peat drainage depth reduces the GHG emissions. • Nature conservation initiatives reduce GHG emissions and nature occupation of palm oil production. • Capturing the biogas produced in palm oil mill effluents (POME) treatment reduces GHG emissions. • Using the captured biogas in boiler or biogas engine further abates the GHG emissions of palm oil.

Agricultural peatlands conservation: How does the addition of plant biomass and copper affect soil fertility?

AbstractSubsidence, erosion, and degradation in agricultural peatlands are leading to the disappearance of highly fertile farmland. This study investigated two strategies aimed at extending the lifespan of cultivated peat soils: the application of straw and wood chips to compensate for soil losses and the application of copper (Cu) to slow peat decomposition, based on previous recommendations. Peat soil samples (270 g) were amended with 11 t ha–1 of biomass materials (14.8 g kg–1) and 235.6 mg Cu kg–1 and incubated in glass jars at constant temperature and water content. Thirty chemical parameters were then monitored over a 56‐d period through repeated soil sampling. Discriminant analysis showed that the addition of biomass had the greatest affect on nitrogen (N) availability, immobilizing 7.8 to 12.1 kg of inorganic N per metric ton of incorporated biomass. Considering that peat soils may require from 4 to 40 t biomass ha–1 yr–1 to reach carbon equilibrium, the tested biomass materials could immobilize from 34 to 500 kg ha–1 of N if confirmed at the field scale. This may help capture excess N but may also limit crop growth. Alternatively, slowing decomposition could reduce both biomass requirements and N immobilization. However, the results show that Cu had little effect on parameters linked to organic matter decomposition. Indeed, dissolved organic carbon was decreased by 11% in Cu‐treated soils. A longer‐term study should be conducted to confirm these observations at the field scale, thus helping to develop conservation strategies suitable for agricultural production.

Nitrous Oxide Emissions in Pineapple Cultivation on a Tropical Peat Soil

Farming systems on peat soils are novel, considering the complexities of these organic soil. Since peat soils effectively capture greenhouse gases in their natural state, cultivating peat soils with annual or perennial crops such as pineapples necessitates the monitoring of nitrous oxide (N2O) emissions, especially from cultivated peat lands, due to a lack of data on N2O emissions. An on-farm experiment was carried out to determine the movement of N2O in pineapple production on peat soil. Additionally, the experiment was carried out to determine if the peat soil temperature and the N2O emissions were related. The chamber method was used to capture the N2O fluxes daily (for dry and wet seasons) after which gas chromatography was used to determine N2O followed by expressing the emission of this gas in t ha−1 yr−1. The movement of N2O horizontally (832 t N2O ha−1 yr−1) during the dry period was higher than in the wet period (599 t N2O ha−1 yr−1) because of C and N substrate in the peat soil, in addition to the fertilizer used in fertilizing the pineapple plants. The vertical movement of N2O (44 t N2O ha−1 yr−1) was higher in the dry season relative to N2O emission (38 t N2O ha−1 yr−1) during the wet season because of nitrification and denitrification of N fertilizer. The peat soil temperature did not affect the direction (horizontal and vertical) of the N2O emission, suggesting that these factors are not related. Therefore, it can be concluded that N2O movement in peat soils under pineapple cultivation on peat lands occurs horizontally and vertically, regardless of season, and there is a need to ensure minimum tilling of the cultivated peat soils to prevent them from being an N2O source instead of an N2O sink.

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (−30 cm and −50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N2O and CH4 fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N2O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at −15 cm and −40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Horizontal and vertical emissions of methane from peat soils

Methane emission depends on the rates of methane production, consumption and ability of soil and plants to transport the gas to the soil surface and also within soil particles. The objective of this study was to determine CH4 fluxes horizontally and vertically from the floor and wall of the pit of a tropical peat soil. The horizontal emissions in the dry and wet seasons were 2.96 t CH4 ha-1yr-1 and 4.27 t CH4 ha-1yr-1, respectively and the vertical emissions were 0.36 t CH4 ha-1yr-1 and 0.51 t CH4 ha-1yr-1, respectively. The total amount of the horizontal and vertical emissions in the dry and wet seasons were 3.32 t CH4 ha-1yr-1 and 4.78 t CH4 ha-1yr-1, respectively. Horizontal emission was higher in the wet season due to an increase in the water table which resulted in an increase of CH4 emission. Thus, there is a need for direct CH4 measurement from cultivated peat soils to ensure that CH4 emission is neither underestimated nor overestimated.
 J Bangladesh Agril Univ 17(3): 359–362, 2019

Thermal conductivity of unfrozen and partially frozen managed peat soils

Detailed, accurate information on soil temperature is crucial for understanding processes leading to solute leaching and greenhouse gas (GHG) emissions from managed peat soils, but few studies have attempted to study these processes in detail. Drained peat soils have different characteristics from pristine peat. Cultivated peat soils, in particular, have high mineral matter content in the plough layer, due to mineralisation of peat and, sometimes, addition of mineral material. This study examined the effect of mineral matter content on thermal conductivity (λ) in partially frozen and unfrozen peat samples. Effect of change in temperature from −3 °C to −10 °C on thermal conductivity was also estimated. Three existing models for estimating the thermal conductivity of organic soils were assessed for their suitability for cultivated drained peat soils. The thermal conductivity of peat samples with three different levels of mineral matter content was determined, using the single probe method, in the saturated state and when subjected to at least two different matric potentials at five different temperatures (+10 °C, + 1 °C, −3 °C, −5 °C and −10 °C). The results showed that λ values differed between peat soils depending on mineral matter content, ice content and moisture content. The samples with the highest mineral matter content and bulk density had higher thermal conductivity at positive temperatures and to a lesser extent, at freezing temperatures, when volumetric water content and volume of water-free pores was similar. Most soil samples, especially those with no added mineral soil, were not fully frozen at −3 °C and −5 °C, but this had minor effect on thermal conductivity compared with values measured at −10 °C. The Brovka-Rovdan model proved reasonably good at predicting frozen thermal conductivity in sand-enriched peat soils, while the de Vries model proved best at estimating thermal conductivity for unfrozen peat samples. We provide a first estimate of the thermal conductivity of (partially) frozen cultivated peat measured using undisturbed samples. These results can be used to parameterise numerical heat transport models for simulating soil processes and GHG emissions.

Carbon capture efficiency, yield, nutrient uptake and trafficability of different grass species on a cultivated peat soil

Loss of organic matter from cultivated peat soils is a threat to farmers, due to the surface subsidence associated with organic matter loss, and to the atmosphere, due to CO2 and N2O emissions from the soil. In a three-year field experiment (2015–2017) on a drained, cultivated fen peat in southern Sweden, we tested whether reed canary grass (Phalaris arundinacea L.) and tall fescue (Festuca arundinacea Schreb.) perform better on peat soils than the commonly grown timothy grass (Phleum pratense L.), without increasing greenhouse gas emissions. In the experiment, we compared yield, nutrient uptake, penetration resistance and loss of organic matter measured as greenhouse gas emissions (CO2, N2O and CH4). Yield of timothy was significantly lower than that of reed canary grass and tall fescue in 2016, and lower than that of reed canary grass in 2017. Yield level increased over time, with total dry matter yield in 2017 of 11.7 Mg ha−1 yr−1 for timothy, 13.5 Mg ha−1 yr−1 for tall fescue and 14.3 Mg ha−1 yr−1 for reed canary grass. Total removal of all macronutrients in 2016 was higher in reed canary grass and tall fescue than in timothy. For nitrogen (N), reed canary grass removed a total of 173 kg N ha−1 yr−1, tall fescue 169 kg ha−1 yr−1 and timothy 121 kg ha−1 yr−1, while the fertilisation rate was only 50 kg N ha−1. There were no differences in trafficability, measured as penetration resistance. Measurements of greenhouse gas emissions in the snow-free season in 2016 and 2017 using manual dark chambers (CO2, N2O and CH4) and in 2016 automatic dark chambers (CO2) revealed only small differences in CO2 emissions between the treatments. The N2O emissions were also low and CH4 emissions were very low and in general negative. The estimated carbon capture efficiency (ratio of C in aboveground biomass plus roots to emitted CO2-C measured by the automatic chambers) for the growing season (May–October) in 2016 was lowest for timothy (0.61) and higher for reed canary grass and tall fescue (0.70 and 0.70, respectively). Reed canary grass and tall fescue are thus promising alternatives to timothy on peat soils regarding yield, nutrient removal and carbon capture efficiency.

Methane Emission from Pineapple Cultivation on a Tropical Peatland at Saratok, Malaysia

Information on methane emission in pineapple cultivation on peatlands is scarce. Methane emission in pineapple cultivation is important as 90% of pineapples are grown on the peat soils of Malaysia. It is essential to determine methane emission in pineapple cultivation because pineapples are Crassulacean acid metabolism plants whose effects on methane could be different from other crops grown on tropical peat soils. Methane emissions from root respiration, microbial respiration, and oxidative peat decomposition were determined in a lysimeter experiment. There were three treatments: peat soil cultivated with pineapple, bare peat soil, and bare peat soil fumigated with chloroform. Methane emissions from peat soil cultivated with pineapple, bare peat soil, and bare peat soil fumigated with chloroform were 0.65 t/ha/yr, 0.75 t/ha/yr, and 0.75 t/ha/yr, respectively. The lower methane emissions are consistent with the general believe that methane emission from cultivated peat soils is lower than those of anaerobic or water logged peat soils. Soil methane emission was affected by nitrogen fertilization under pineapple cultivation but the converse was true for soil temperature nor soil moisture.

Isolation of Cellulolytic Bacteria from Peat Soils as Decomposer of Oil Palm Empty Fruit Bunch

The aim of the research was to find out potential strainsof cellulolytic bacteria isolated from two tropical peat soils and to studythe potency of the isolated bacteria to decompose oil palm empty fruit bunch (EFB). The research was carried out in two stages: (1) isolation of cellulolytic bacteria from peat soils and (2) testing the potency of isolated bacteria to decompose oil palm EFB. The cellulolytic bacteria were isolated from two peat soils, i.e. a natural peat soil (forest) and a cultivated peat soil (has been used as agriculture land). Isolation of cellulolytic bacteria was conducted by preparing a series dilution of culture solutions using a streak plate method in a carboxymethyl cellulose(CMC) selective medium.Isolates that were able to form clear zones surrounding their bacterial colony were further tested to study the potency of the isolates to decompose cellulose in oil palm EFB. The cellulolytic activity of the selected isolates were further determined via production of reducing sugars in an oil palm EFB liquid medium using Nelson-Somogyi method. The results showed that there are six isolates of cellulolytic bacteria that have been identified in two tropical peat soils used in the current study. Two isolates are identified in a natural peat soil (forest) and four isolates are identified in a cultivated peat soil. The isolates collected are identified as Bacillus sp., Pseudomonassp. and Staphylococcus sp. Among the isolates, an isolate of GS II-1 produces the highest concentration of reducing sugars, namely 0.1012 unitmL-1or 101 ppm, indicating that the isolate of GS II-1 is highly potential to decompose oil palm EFB. Therefore, the isolate of GS II-1 can be used as a decomposer in the bio-conversion processes of oil palm EFB.Keywords: isolation, bacteria, cellulolytic, oil palm empty fruit bunch (EFB), peat soil

Greenhouse gas emissions from intensively managed peat soils in an arable production system

Organic-rich, eutrophic peat soils (Histosols) represent a major store of carbon (C) within the terrestrial biosphere. However, these soils are also highly susceptible to damage, particularly when used for intensive agricultural production. Sustainable management of such soils is contingent upon improved understanding of the impact of their management on the environment. In this context, we report the first annual budget of greenhouse gas emissions from temperate peat soils under intensive horticultural production. Fluxes of CO2, N2O and CH4 were measured using static chambers on three farms along an organic matter loss gradient (∼20%, ∼35%, and ∼70% soil organic matter (SOM) content respectively), under a number of commercially important crops in similar rotations. Cumulative annual fluxes of CO2 in fallow and cropped soils were large and ranged from 13.0±2.4 to 30.9±2.5t CO2-eha−1y−1, showing a general increase with SOM, and on cropped compared to bare soils. Annual emissions of N2O varied from 5.0±0.7 to 13.9±1.9t CO2-eha−1y−1, and CH4 from −0.02±0.08 to 0.04±0.02t CO2-eha−1y−1; neither showed a significant relationship with either SOM content or cropping. Distinct seasonal patterns of CO2 and N2O fluxes were observed, corresponding to significant correlations between emissions and soil and air temperature, soil moisture content, water table depth, and soil nitrate on some soil types. No discernible seasonal pattern in CH4 fluxes was observed, and very few significant correlations with soil environmental variables were found. Compared to emissions estimates suggested in IPCC inventory guidelines for cultivated peat soils, the observed emissions in this study were relatively high, and net annual fluxes of CO2 and CH4 are equivalent to a loss of soil depth of 0.33–0.75cmy−1. We conclude that arable farming is promoting extreme mineralization of the soil’s organic carbon reserves and that a change in land use or management regime is needed to protect and preserve this natural capital.

Horizontal and vertical emissions of methane from a drained tropical peat soil cultivated with Pineapple (Ananas comosus (L.) Merr.)

Drained tropical peat soils especially for agricultural purposes could lead to methane (CH4) emission into the atmosphere. Methane emission from peat soils to the atmosphere depends on rates of methane production, consumption and ability of the soil and plants to transport the gas to soil’s surface and also within soil particles. The objective of this study was to determine CH4 fluxes horizontally and vertically from the floor and wall of the pit of a tropical peat soils cultivated with Ananas comosus (L.) Merr. and to determine the relationship between CH4 transportation and CH4 emission from a drained tropical peat soils. Gas samplings were conducted in the dry and wet seasons. The horizontal emission of CH4 in the dry and wet seasons were 2.96 t CH4 ha-1yr-1 and 4.27 t CH4 ha-1yr-1, respectively. The vertical emission of CH4 in the dry and wet seasons were 0.38 t CH4 ha-1yr-1 and 0.50 t CH4 ha-1yr-1, respectively. The total amount of the horizontal and vertical CH4 emissions in the dry and wet seasons were 3.34 t CH4 ha-1yr-1 and 4.47 t CH4 ha-1yr-1, respectively. Horizontal emission of CH4 was higher in the wet season due to increase in water table which resulted in increase of CH4 emission. Therefore, it can be concluded that horizontal emission of CH4 is higher than vertical emission suggesting that there is a need for direct CH4 measurement from cultivated peat soils to ensure that CH4 emission is neither underestimated nor overestimated.

Nitrous oxide and methane fluxes during the growing season from cultivated peat soils, peaty marl and gyttja clay under different cropping systems

ABSTRACTDrainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N2O and influence CH4 fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N2O and CH4 fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N2O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919 µg N2O m−2 h−1, with peaks on individual sampling occasions of up to 3317 µg N2O m−2 h−1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N2O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH4 fluxes. Median seasonal CH4 flux from the different sites ranged from uptake of 36 µg CH4 m−2 h−1 to release of 4.5 µg CH4 m−2 h−1. From our results, it was concluded that farmers cannot mitigate N2O emissions during the growing season or influence CH4 fluxes by changing the cropping system in the field.

Physical and Chemical Properties of Cultivated Peat Soils in Four Trial Sites of ICCTF in Kalimantan and Sumatra, Indonesia

The large distribution of peat soils in Indonesia have important role in carbon stock and greenhouse gas emission which contribute to global warming issue. The objective of this study was to characterize physical and chemical properties of cultivated peat soils in four trial sites of Indonesia Climate Change Trust Fund (ICCTF) in Central Kalimantan, South Kalimantan, Riau and Jambi Provinces to provide a baseline data by a greenhouse gas emission study. Detailed soil observations were conducted using grid system with spacing of 25 × 50 m. A total of 16 representative peat soil profiles consisting of 74 soil samples of horizons were selected for laboratory analyses. The results showed that peat maturity varied from hemic to sapric in the surface layers and hemic in the subsurface layers, except in Site-2 that was fibric. The peat thickness ranged respectively from 5.4 to 7.0 m in Site-1 and Site-3, and from 0.5 to 2.5 m in site-2 and site-4, and all overlying fine-textured mineral soil (substratum). Depth of water table varied from 10 to 30 cm in Site-2 and Site-4, and from 30 to 70 cm in Site-1 and Site-3. Fiber content ranged from 13 to 57% and increased with depth indicating the peat was less decomposed. The bulk density was very low (0.07-0.24 g cm-3) and negatively correlated to fiber content (r = 0.74 for Kalimantan and r = 0.66 for Sumatra). The ash content was low (0.1-8.5%) and negatively correlated to organic carbon content (r = 0.89 for Kalimantan and r = 0.65 for Sumatra). Soil CEC was high and positively correlated to organic carbon content (r = 0.86 for Kalimantan and r = 0.93 for Sumatra). These soils showed very acid reaction (pH 3.3-4.7), low content of exchangeable bases and total P2O5 and K2O (HCl 25%). Based on these properties, the peat soils were grouped as oligotrophic ombrogenous peat. The estimated carbon stock for all the trial sites with total extent of 22.58 ha was 57,282 Mg C. The variation of thickness, maturity, and water table depth will imply to the magnitude of carbon reserves and greenhouse gas emissions. [How to Cite: Hikmatullah and Sukarman. 2014. Physical and Chemical Properties of Cultivated Peat Soils in Four Trial Sites of ICCTF in Kalimantan and Sumatra, Indonesia. J Trop Soils 19: 131-141. Doi: 10.5400/jts.2014.19.3.131]

MANGANESE SPECIATION IN SELECTED AGRICULTURAL SOILS OF PENINSULAR MALAYSIA

Manganese speciation in selected agricultural soils of Peninsular Malaysia is discussed in this study. Manganese concentration in the Easily Leacheable and Ion Exchangeable (ELFE), Acid Reducible (AR), Organic Oxidizable (OO) and Resistant (RR) fractions of soils developed on weathered rocks, soils of mixed nature, alluvium and peat deposits are descri bed. The total manganese concentration in soils developed on weathered rocks was found to be higher than that in soils of mixed nature, alluvium and p eat deposits because of the occurrence of resistant man ganese oxide at the topsoils. Manganese speciation in paddy soils is influenced by the redox condition re sulting from the alternate flooding and drying of t he soils. Under reducing conditions, this metal tends to get dissolved and be available for plant uptake. Upon oxidation, manganese is precipitated into the acid reducible fraction as poorly crystalline manganese oxide and hydroxide and/or the resistant Fe-Mn mottles. I n non-paddy cultivated alluvial soils, manganese speciation varies widely and is less understood. Fo r the non-paddy cultivated peat soils, manganese is mainly associated with organic material, as indicat ed by the high manganese concentration in the OO fraction.

Community-specific pH response of denitrification: experiments with cells extracted from organic soils

Denitrifying prokaryotes are phylogenetically and functionally diverse. Little is known about the relationship between soil denitrifier community composition and functional traits. We extracted bacterial cells from three cultivated peat soils with contrasting native pH by density gradient centrifugation and investigated their kinetics of oxygen depletion and NO2 -, NO, N(2) O and N(2) accumulation during initially hypoxic batch incubations (0.5-1 μM O(2)) in minimal medium buffered at either pH 5.4 or 7.1 (2 mM glutamate, 2 mM NO3 -). The three communities differed strikingly in NO2 - accumulation and transient N(2) O accumulation at the two pH levels, whereas NO peak concentrations (24-53 nM) were similar across all communities and pH treatments. The results confirm that the communities represent different denitrification regulatory phenotypes, as indicated by previous denitrification bioassays with nonbuffered slurries of the same three soils. The composition of the extracted cells resembled that of the parent soils (PCR-TRFLP analyses of 16S rRNA genes, nirK, nirS and nosZ), which were found to differ profoundly in their genetic composition (Braker et al., ). Together, this suggests that direct pH response of denitrification depends on denitrifier community composition, with implications for the propensity of soils to emit N(2) O to the atmosphere.

Plant-derived CO2 flux from cultivated peat soils

Methods used to estimate the CO2 emission from soil commonly measure the total CO2 flux. To be able to quantify the net CO2 emission from cultivated peat soils there is a need to distinguish between soil organic matter-derived CO2 respiration and plant-derived respiration. In this investigation we used the root exclusion method to separate the plant-derived respiration from total CO2 emission. The plant-derived contribution was estimated to be between 27 and 63% of total CO2 emission depending on soil type and season. We also found a relationship between soil temperature, biomass growth and CO2 efflux, which can be used to estimate plant-derived respiration. Due to the priming effect the root exclusion method is less reliable late in the season.

Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil

A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Orke, a typical cultivated fen peat with low pH and high organic matter content and Majnegarden, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, O29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO2, CH4 and N2O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO2 emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N2O emissions peaked in springtime and CH4 emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO2 equivalents m-2. The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates.