Decomposed Sphagnum Peat Research Articles

Mitigating greenhouse gas fluxes from cultivated organic soils with raised water table

Cultivated organic soils are a remarkable source of greenhouse gases (GHG) in many countries. Keeping the ground water table as high as possible could lower the mineralization rate of the peat and thus the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) from these soils. We studied the effect of raised water table on the emissions of N2O, CO2 and methane (CH4) from undisturbed peat soil profiles of six different Finnish cultivated organic soils during a 5-week outdoor mesocosm experiment. The aim was to determine an optimum water table that would enable grass cultivation but lower the net gas balance of the soil. Raised water table decreased the GHG emissions from each peat type ranging from weakly decomposed Sphagnum peat to highly humified Carex peat. Based on the results, the optimum water table would be 30 cm below the soil surface. The average reduction of the total net emissions with a raise of water table from a typical drainage depth of 70 to 30 cm was 42 % in the outdoors mesocosm experiment and 23 % at a constant temperature (+6 °C). The emissions of both CO2 and N2O declined and the net consumption of CH4 changed to net production as the water table rose. The results were confirmed by long-term measurements at one of the sampled sites. As a conclusion, we see that promoting drainage systems enabling raising of the ground water table and cultivation of crops capable of producing good yields also in wet conditions would be beneficial for the GHG mitigation in agriculture.

OPTIMIZATION OF CLAY AMENDMENT FOR IMPROVING THE RE-WETTABILITY OF PEAT-BASED GROWING MEDIA

Peat is an important growing media constituent which exposes hydrophobic properties if getting dry. The addition of clay induces a coated surface with hydro-philic properties which improves the re-wettability. The formation of an effective clay coating on peat during processing depends predominantly on the amount of clay applied, clay fineness and mineral parameters. Peat surfaces consist mainly of C. When these are covered with clay minerals rich in Si, the degree of coverage can be described as the C/Si ratio, determined by energy dispersive X-ray spectroscopy. A moderately decomposed sphagnum peat was amended with four different clays from the Rhenish Massif, Germany (10, 20, and 30 kg clay/m³). Aggregate size varied from <0.063 to 2.0-4.0 mm and water-uptake characteristics were determined using a capillary-rise method. Water uptake was improved for all samples by amendment of clay, strongly depending on clay parameters. At C/Si ratios <20, where the surfaces of peat are most completely coated with clay minerals, all clay-peat systems showed the highest water uptake rate. Saprolitic and translocated clays, consisting mainly of illite and kaolinite, had the strongest effect on surface coverage degree. Here already 20 kg/m³ were sufficient to reach lowest C/Si ratios indicating maximum coverage degree. These clays showed fastest water uptake (50 vol. % within 10 min), whereas bentonite showed only minor effects (1.47 to 3.63 (% v/v)/min). A translocated clay was most effective to improve the water uptake rate, admixing small clay amounts. The results show a good correlation of the C/Si ratio and re-wettability. The determination of the C/Si ratio in a relatively short procedure is a method to estimate the water uptake rate of different horticultural growing media. The combination of these methods can be used to identify suitable clays for improving re-wettability, optimum clay fineness and the amount of clay needed.

Prospects for sphagnum peat as a source of fullerenes

The modification of slightly decomposed sphagnum peat for the synthesis of fullerenes is considered. Topographic images of the carbon nanotubes first synthesized on that basis are presented.

A Laboratory Device for Continual Measurement of Water Retention and Shrink/Swell Properties during Drying/Wetting Cycles

The precise measurement of the water retention and shrink/swell properties of growing media or soil over time is important for the effective management of irrigation and fertilization. A new apparatus was developed for simultaneously and continuously measuring the water retention and shrink/swell properties of growing media during several drying/wetting cycles with varying intensities (0↔–5 kPa, 0↔–10 kPa, 0↔–32 kPa). The measurements on slightly decomposed Sphagnum peat showed encouraging results. Regardless of the intensity of drying, water retention and shrink/swell properties are mainly modified after the first drying process, resulting in degradation of density and water retention, whereas these properties are unaffected by the other cycles, even if hysteresis phenomena are always shown to take place. Variations in drying intensity reveal different physical behaviors with an inflection point observed (i.e., a change in physical behavior) for the shrink/swell and water retention curves for the highest intensity tested (from –20 kPa).

Influence of Clay Addition on Physical Properties and Wettability of Peat-growing Media

The role of clay incorporation on the physical properties and wettability of peat-growing media was assessed from water retention curves and from contact angle and water drop penetration time measurements, respectively. Two peat substrates presenting different degrees of decomposition (weakly and highly decomposed Sphagnum peat) were used and mixed with clay in the form of powder with a peat:clay ratio of 90:10 (by vol.). Results indicated relatively little change in water retention resulting from clay incorporation in the peat-growing media tested. On the other hand, they showed a significant improvement of the wettability of both substrates in the driest conditions when peat-growing media presented a pronounced hydrophobic character, whereas the wettability of materials was not changed in the wettest conditions when they were largely hydrophilic. The influence of the degree of peat decomposition was also observed with somewhat higher wettability for the weakly decomposed peat:clay mixture than for the highly decomposed peat:clay mixture. Because the hydrophobic character of highly decomposed peat is more pronounced and appears at a higher water content than weakly decomposed peat, the effect of clay addition also appears at higher water contents for highly decomposed peat. Incorporating clay into peat-growing media should be considered for its ability to improve the wettability of growing media with a hydrophobic character (i.e., to improve the ability of the growing media to be rewetted) rather than only its ability to influence the water retention characteristics of the growing media.

NITROGEN BALANCE OF THREE ORGANIC POTTING-MEDIA IN RELATION TO THE ADDED CARBON SOURCES

NITROGEN BALANCE OF THREE ORGANIC POTTING-MEDIA IN RELATION TO THE ADDED CARBON SOURCES

In situ measurements of the thermal properties of a northern peatland: Implications for peatland temperature models

Carbon uptake/release in peat soils (the latter especially in the form of methane) is strongly dependent on soil temperature. However, previous peatland temperature models have not represented soil temperatures accurately due to either errors in their parameterization or errors in the representation of heat transfer processes. Dual probe heat pulse sensors (DPHPS) and triple‐probe heat pulse sensors (TPHPS) were used to provide detailed in situ measurements of the soil thermal properties of Sphagnum peat and the advective liquid heat flux resulting from percolating rainfall. The difficulties of applying the DPHPS approach within poorly decomposed Sphagnum peat are first considered. Our results suggest that measurement‐induced advective vapor and liquid heat fluxes occurred when using the DPHPS. The analytical equations normally used to calculate the thermal diffusivity and volumetric heat capacity (C) from DPHPS measurements, therefore, cannot be applied within unsaturated Sphagnum peat. However, a numerical approach enabled the soil thermal properties to be estimated when an instrument‐induced advective vapor flux was significant. When an instrument‐induced advective liquid heat flux was significant, the relevant DPHPS data were identified and rejected. The measurements of the soil thermal properties were used to (1) develop an empirical model of the vertical variations in C through the unsaturated zone of poorly decomposed Sphagnum peat and (2) to develop an empirical relationship between the thermal conductivity (k) and C. The TPHPS measurements showed that the advective heat flux due to percolating rainfall occurred for a maximum of 24 hours after rainfall events. Its influence on soil temperatures may therefore be negligible.

SUPPRESSION OF SOILBORNE PATHOGENS BY COMPOST: SUPPRESSIVE EFFECTS OF GRAPE MARC COMPOST ON PHYTOPATHOGENIC OOMYCETES

SUPPRESSION OF SOILBORNE PATHOGENS BY COMPOST: SUPPRESSIVE EFFECTS OF GRAPE MARC COMPOST ON PHYTOPATHOGENIC OOMYCETES

Reduction of bacterial leaf spot severity on radish, lettuce, and tomato plants grown in compost-amended potting mixes

Compost-amended substrates offer the potential for management of diseases caused by soilborne as well as foliar plant pathogens. In this study, the efficacy of composted pine bark mix fortified with the biocontrol agent Trichoderma hamatum 382 (FCPB) against bacterial leaf spot of radish, lettuce, and tomato under controlled environment conditions was evaluated. Plants grown in the FCPB mix and inoculated with bacterial leaf spot pathogens were less severely diseased than plants grown in commercial peat mix or vermiculite. In some cases, plants were also grown in a composted cow manure mix or in a steam-treated compost-amended greenhouse soil, and these plants were also less severely diseased. Infected radish and tomato plants grown in these compost-amended substrates also harbored significantly smaller populations of Xanthomonas campestris pv. armoraciae and Xanthomonas campestris pv. vesicatoria, respectively. The disease-suppression effect of the FCPB mix was lost by autoclaving and restored by reinoculating the autoclaved FCPB mix with nonautoclaved FCPB mix. However, the disease-suppression effect varied among the batches of FCPB mix used. In contrast, vermiculite and a highly decomposed sphagnum peat mix consistently failed to suppress these diseases. These results suggest that producing vegetable seedlings in FCPB mix or compost-based substrates may provide initial protection against bacterial leaf spot pathogens.

Effect of Potting Mix Microbial Carrying Capacity on Biological Control of Rhizoctonia Damping-Off of Radish and Rhizoctonia Crown and Root Rot of Poinsettia

ABSTRACT Potting mixes prepared with dark, highly decomposed Sphagnum peat, with light, less decomposed Sphagnum peat, or with composted pine bark, all three of which were colonized by indigenous microorganisms, failed to consistently suppress Rhizoctonia damping-off of radish or Rhizoctonia crown and root rot of poinsettia. Inoculation of these mixes with Chryseobacterium gleum (C(299)R(2)) and Trichoderma hamatum 382 (T(382)) significantly reduced the severity of both diseases in the composted pine bark mix in which both biocontrol agents maintained high populations over 90 days. These microorganisms were less effective against damping-off in the light and dark peat mixes, respectively, in which populations of C(299)R(2) declined. In contrast, crown and root rot, a disease that is severe late in the crop, was suppressed in all three types of mixes. High populations of T(382) in all three mixes late during the cropping cycle may have contributed to control of this disease.

Effect of biogenic gas bubbles on water flow through poorly decomposed blanket peat

A laboratory investigation was used to determine whether biogenic gas bubbles accumulate and block water‐conducting pores below the water table in poorly decomposed Sphagnum peat. We found that biogenic gas bubbles did accumulate under realistic incubation temperatures. At the end of incubations at 10.5°C, volumetric water contents in two peat samples decreased to between 0.8 and 0.85 (porosity of the samples ranged from 0.96 to 0.97), indicating that the peat was considerably undersaturated with respect to water. Methane was found to be an important constituent of the gas bubbles. The presence of gas bubbles appeared to have a major effect on hydraulic conductivity (K). In control incubations, prior to which the peat had been irradiated and dosed with a biocide, biogenic gas bubbles did not accumulate, and K was 5–8 times higher than at the end of the microbially active incubations. Our results suggest that biogenic gas bubbles have a potentially significant effect on seepage in peat soils.

Compost-Induced Systemic Acquired Resistance in Cucumber to Pythium Root Rot and Anthracnose

Pythium root and stem rots cause problems in production of greenhouse and nursery crops. Composts, however, can provide biological control of these diseases. We planted and germinated cucumber (Cucumis sativus 'Straight Eight') seeds in compost-amended (spruce or pine bark composts) or in highly decomposed sphagnum peat (H 4 on the von Post decomposition scale) mixes suppressive and conducive to Pythium root rot, respectively. Two-week-old seedlings were transplanted, using the split-root technique, into the compost-amended mixes and the peat mix. Split-root pairings were peat/compost, peat/peat, and compost/compost. Only one side of the split roots was grown in potting mix infested with Pythium ultimum and P. aphanidermatum. Root rot in the infested mix, averaged across all split-root pairings, was significantly (P ≤ 0.05) less severe and mean root dry weights were significantly (P ≤ 0.05) higher in plants germinated in the compost-amended mixes than in the peat mix. Also, root rot in the infested peat mix was significantly less severe on roots paired with the compost-amended mixes than those paired with the peat mix. Plants grown from seed in the compost-amended mixes or the peat mix also were tested for resistance to anthracnose. Three weeks after planting, anthracnose on the second leaf of cucumber 'Straight Eight' inoculated with Colletotrichum orbiculare was significantly less severe (P ≤ 0.05) on plants grown in the compost-amended mixes than in the peat mix. Peroxidase activity, a putative marker of systemic acquired resistance (SAR) in cucumber, was significantly (P ≤ 0.05) enhanced in plants grown in the compost-amended mixes compared to the peat mix. However, the activity of a peroxidase isozyme in the second leaf of cucumber plants was greater when plants were grown in compost as well as after prior inoculation with C. orbiculare than if grown in peat and with or without prior inoculation. The interaction of compost and the pathogen appeared critical for rapid activation of SAR-associated gene expression in cucumber plants.

Direct seeding black spruce on peatlands: fifth-year results

Black spruce seedspot and broadcast seeding experiments were completed on peatlands at four locations in northeastern Ontario. Poorly decomposed Sphagnum peat was the best seedbed for black spruce, with establishment ratios from 20 to 50 seedlings per 100 seeds sown. An effective seeding rate (actual seeding rate × receptive seedbed area fraction) of six or seven seeds per quadrat is required to obtain quadrat stocking of 80% or greater. Fifth-year seedling heights averaged from 8 to 17 cm. Black spruce advance growth is often an important source of regeneration on peatlands and must be considered in developing seeding prescriptions. Key words: black spruce, direct seeding, peatlands, seedbed type, Ontario, advance growth

Sucker production from root cuttings of Populus tremula in relation to growing conditions

Root cuttings from 10‐year‐old European aspen (Populus tremula L.) were rooted in decomposed Sphagnum peat and sand. The root cuttings were exposed to different temperatures (10 and 25°C) and a light intensity of 300 umol m−2s−1 for 83 days. Five levels of root depth were used: 2, 4, 6, 8 and 16 cm. Suckers of another clone of 15‐year‐old European aspen were exposed to different light intensities (300, 150, 75 and 30 umolm−2s−1) for 120 days. The percentage of sprouting aspen cuttings was highest in the upper part of the peat (2–6 cm). The total number of suckers was highest at 4 and 6 cm root depths. Dry weights of suckers at 4 and 6 cm root depths were 4200 and 3 840 mg at 25°C and 340 and 180 mg at 10°C, respectively, but were negligible at other root depths. Cuttings produced more suckers when exposed to 25°C than to 10°C. Most of the suckers were produced during 15–25 days after planting. Dry weights of suckers exposed to 300, 150, 75 and 30 umolm−2s−3 were 1831, 2280, 1107 and 323 mg, respectively. ...

Effect of pH on the behaviour of various iron chelates in sphagnum (moss) peat

Abstract An incubation experiment was conducted to examine the stability and water solubility of four different iron chelates in slightly decomposed sphagnum peat as affected by pH and time of incubation. Decrease in soluble iron upon addition of iron chelates is caused by fixation and by replacement of the chelated iron by calcium at high pH. At low pH (pH‐H2O 4.35), recovery of soluble iron after six weeks decreases in the order:Fe‐DTPA > Fe‐EDTA > Fe‐EDDHA > Fe‐HEEDTA. At high pH (pH ‐ H2O 7.25 and 7.85) this order is: Fe‐EDDHA ≫Fe‐DTPA > Fe‐HEEDTA > Fe‐EDTA. In cultivating plants at low pH, Fe‐EDTA and Fe‐DTPA will be the more efficient iron sources. At high pH, however, only Fe‐EDDHA supplies sufficient soluble iron for a long period. Fe‐HEEDTA is a poor iron source at all pH‐levels because of fixation and, at high pH, substitution of calcium for iron. It was demonstrated that it is necessary to characterize commercial iron chelates by gel chromatography before testing them in plant performance studies.

Penetration of Bog Peats and Lake Sediments by Tritium from Atmospheric Fallout

Tritium in surface bog peats of the Red Lake wetland, northern Minnesota, exhibits about the same concentration as in atmospheric precipitation, which is still appreciably enriched by tritium from nuclear weapon testing. Past input pulses are not preserved in the peat profile, and the pattern of subsurface decline suggests that most of the modern precipitation rich in tritium is removed rapidly by evapotranspiration and by lateral runoff within the top 1.5 m of the 3.5—m thickness of little—decomposed Sphagnum peat at the crest of the raised bog. However, some bomb tritium has penetrated, presumably by molecular diffusion, down to the discontinuity between the highly permeable Sphagnum peat and the underlying well—decomposed and much less permeable fen peat. In profundal lake sediments of four Minnesota lakes the influence of highly enriched precipitation from the early 1960's has likewise been largely transitory and of major significance only in sediment depths of less than 1 m, although some penetration below the depth has occurred, presumably by molecular diffusion.