Soil Redox Potential Research Articles

Azolla planting reduces methane emission and nitrogen fertilizer application in double rice cropping system in southern China

Rice paddies are a major source of methane. How to reduce the methane emission in the paddy field without decreasing the yield has become a major concern of scientists, environmental groups, and agricultural policymakers worldwide. Azolla, used as a dual crop in rice cultivation, has multiple agronomic benefits. However, the effects of the dual cropping of Azolla on methane emissions of double rice cropping paddies have not yet been reported. Here, we conducted a 3-year field experiment to evaluate the impacts of rice + Azolla on methane emission and rice yield in a double rice cropping system. The results indicated that the rice + Azolla without N fertilizer and with moderate N fertilizer (200 kg N ha−1 a−1) significantly reduced methane emissions over the rice cycle by 12.3 and 25.3% compared with the conventional rice cropping with common N fertilizer (400 kg N ha−1 a−1), respectively. The reason for the trend was because the dual cropping of Azolla has significant effect on dissolved oxygen and soil redox potential, which are key factors for methane emission in this study. The rice yield under the rice + Azolla with moderate N fertilizer annually averaged 12.7 Mg ha−1, which was comparable with that of the conventional rice cropping with common N fertilizer. Moreover, the rice + Azolla with moderate N fertilizer had the lowest yield-scaled methane (25.2 kg Mg−1 grain yield). Here, we showed for the first time that Azolla planting allows sustainable rice production coupled with methane mitigation in double rice cropping systems.

Radial oxygen loss by the cushion plant Eriocaulon schimperi prevents methane emissions from an East-African mountain mire.

Groundwater-fed fens are known sources of methane (CH4 ) emissions to the atmosphere, and these are known to be mediated by the vegetation. In a fen located in the Bale Mountains, Ethiopia, we assessed the effects of a cushion plant(Eriocaulon schimperi) and a sedge (Carex monostachya) on rhizosphere biogeochemistry. Methane and CO2 concentrations and pH were measured in pore-water at different depths in the profile. Redox potentials and NaCl-extractable element concentrations were analysed in soil samples from sites dominated by either E.schimperii or C.monostachya. Nutrient and element concentration were analysed in plant tissues. At Carex-dominated sites, CH4 concentrations increased from 70μmol·l-1 at a depth of 10cm to 130μmol·l-1 at a depth of 100cm. CH4 concentrations at Eriocaulon-dominated sites were almost zero (<1μmol·l-1 ) to a depth of 100cm. Simultaneously, soil redox potentials and CO2 concentrations were higher at Eriocaulon-dominated sites, indicating a low potential for CH4 production and a high potential for CH4 oxidation. Eriocaulon schimperi displayed a root investment strategy to cope with the harsh environment, similar to the cushion plant Astelia pumila in Patagonian bogs. This strategy is characterised by high root/shoot ratios, high root porosity and density under high redox conditions. Both cushion plant species create an aerobic rhizosphere through radial oxygen loss from deep roots, which strongly reduce CH4 fluxes to the atmosphere.

Effects of live wetland plant macrophytes on acidification, redox potential and sulphate content in acid sulphate soils

AbstractUnless properly managed, acid sulphate soils can exert a range of negative environmental impacts, including soil acidification and mobilization of metals and metalloids. Incorporation of organic matter in the form of plant mulches can substantially neutralize sulphuric soils and prevent the oxidation of sulphidic soils. These positive effects of dead plants are largely mediated by bacterial reduction of sulphates to sulphides, using the organic matter as a microbial nutrient source. However, very little is known about the effects of live plants on acid sulphate soils. In this study, we compared pH, Eh and sulphate content of sulphidic and sulphuric soils that were not planted (i.e. unplanted) with those soils planted with the following three common wetland plants: Phragmites, Melaleuca and Typha. Each of these plants is capable of growth in aerobic and flooded soils. In all our experiments, the presence of plants correlated with an increase in soil acidification rather than neutralizing soil acidity when compared to unplanted controls. The mechanism for this appears to be transport of oxygen down the soil profile by aerenchymatous tissue formed in these species, and the release of oxygen into the rhizosphere.

Crop residues exacerbate the negative effects of extreme flooding on soil quality

Extreme flood events are predicted to have a negative impact on soil quality. Currently, there is a lack of information about the effect of agricultural practices on soil functioning and microbial processes under these events. We hypothesized that the impact of flooding on soil quality will be exacerbated when crop residues are present in the soil as they will induce more extreme anaerobicity. A spring extreme flood event (10 °C, 9 weeks) was simulated in mesocosms containing an arable sandy-loam soil low in nutrients. The main treatments were (1) with and without flooding and (2) with and without maize residue addition (8 Mg ha−1). We monitored changes in soil chemical quality indicators (e.g. pH, salinity, Fe3+, P, C, NH4+, NO3− and organic N), greenhouse gas (GHG) emissions (CO2, CH4, N2O) and soil microbial community composition (PLFAs) during a prolonged flood period (9 weeks) and an 8-week “recovery” period after flooding. In comparison to the other treatments, flooding in the presence of crop residues resulted in a dramatic drop in soil redox potential. This was associated with the enhanced release of Fe and C into solution and an increase in CH4 emissions. In contrast, maize residues reduced potential nitrate losses and N2O emissions, possibly due to complete denitrification and microbial N immobilization. Both flooding and maize residues stimulated microbial growth and promoted a shift in microbial community composition. Following floodwater removal, most of the soil quality indicators returned to the levels of the control treatment within 5 weeks. After this short recovery phase, no major impact of flooding could be observed on plant growth (maize pot-grown). Overall, we conclude that both extreme flooding and management regime negatively impact upon a range of soil quality indicators (e.g. redox, GHG emissions); however, the soil showed high resilience and recovered quickly after floodwater removal. Further work is required to investigate the impact of repeated extreme flood events on soil quality and function over longer timescales.

Influencing Mechanism of Eh, pH and Iron on the Release of Arsenic in Paddy Soil

The massive release of soil arsenic and its enrichment in rice are significantly associated with the flooded and anaerobic management in paddy soil. Soil redox potential (Eh), pH and iron oxides exert remarkable impacts on arsenic release, which remain to be explored. In this study, long-term aerobic and anaerobic as well as intermittent aerobic incubation treatments were applied to investigate the influences of Eh, pH and iron content on arsenic release. It was found that anaerobic and flooded treatment contributed to the highest arsenic release. With decreasing Eh, significant enhancement in As(Ⅲ) and As(Ⅴ) contents in soil solution was observed. Particularly, As(Ⅲ) and As(Ⅴ) contents during the second phase increased by 1.37 and 0.99 μg·L-1compared with those in the first phase. Conversely, significant reduction in soil arsenic release (P<0.05) occurred when intermittent aerobic treatment was adopted, and the lowest level of arsenic release was observed along with the longest treatment time (6 d). The exponent relationships between arsenic and soil Eh, pH and Fe2+ content were also established, which indicated that arsenic release could be accelerated by lower pH and elevated Eh. In addition, a significant positive correlation was also found between iron(Ⅱ) content and arsenic content in soil solution. Since low Eh and elevated pH served as critical factors driving arsenic release, intermittent and aerobic water management was proved to be an effective method for the inhibition of arsenic release and uptake and accumulation of arsenic by rice.

Influence of Demographic Location and Solvent Extraction on Pharmacognostical Assessment and Identification of Conessine Content in Different Parts of Holarrhena antidysentrica Through HPTLC Analysis

Abstract: Objective: The present study is aimed at comparative pharmacognostical studies in terms of macroscopic and quantitative microscopy on different solvent (chloroform, methanol and water) extracted leaves, stem and root parts of HA, procured from the Bangalore soil zone, Karnataka, India. Methods: Initially the soil parameters are checked for the presence of various metals and other physicochemical properties. Microscopy and macroscopic analysis were performed to under the arrangement of anatomical structures of cells and tissues. Thereafter HPTLC study was performed to determine the presence of conessine in various parts of Kurchi. Results and discussion: The results revealed the soil is sandy loam with the pH of 7.40, organic carbon content 0.30%, electrical conductivity (EC) was 13.14 mS cm-1 and the soil redox potential was 17.80 mV. Macroscopical and microscopical evaluation of leaf, stem and root gave special identification characters. Phytochemical investigation reveals the presence of alkaloids, carbohydrate, protein, glycoside, saponin, phytosterols and diterpenes. Thereafter, presence of conessine was identified by HPTLC at 192 nm using mobile phase Toluene, Ethylacetate and Dietylamine (6:3:1) and percentage of conessine resulted higher of 0.51 in methanol bark extract followed by 0.48 % in the methanol root extract. This may be due to the soil nature of Bangalore zone and the effect of solvent where the active constituents are soluble maximized to get more yield. Conclusion: Pharmacognostical parameters and conessine content in different parts of Holarrhena antidysentrica through HPTLC was revealed that was dependent on various factors. Key words: Extracts, Holarrhena antidysentrica, HPTLC, preliminary evaluation, solvents

Oxidation of iron sulfides in subsoils of cultivated boreal acid sulfate soil fields – based on soil redox potential and pH measurements

Acid sulfate soil leachates deteriorate the aquatic ecosystems of their recipient waters around the world. In Finland, AS soils are located mainly on the coast of the Baltic Sea, where rivers and estuaries suffer from acid leachates and waters do not meet with the criteria of good water quality set by the EU. Field drainage of cultivated AS soils is attributable to leaching of acidity, but regardless of various mitigation measures, the acidity of discharge water in these areas has not decreased significantly. In order to better understand the pathways involved in the formation of acidity, the redox status of 56 Finnish AS soil fields was examined using redox potential and pH data measured down to 2m. The findings indicated that the oxidation of soils has occurred at depths below the drainage pipes, with the median being at a depth of 1.6m. In fields cultivated for a long time, soil texture had a stronger effect on the depth of the redox interface than the drainage method; open ditch drainage and subsurface drainage; oxidation being faster in sandy and silty soils than in clayey soils. The isostatic land uplift also seems to affect the depth of the redox interface in the long run. Most of the studied fields had been cultivated for at least 30years prior to the study. However, the pH values of the soils were still very low, probably due to actual and retained acidity. The prevention of oxidation of sulfidic materials in subsoils is important, but measures for neutralizing the acidity are needed. Without them it seems that the leaching of acidity will continue and may decrease only slowly. However, severe droughts during summers and the reclamation of unripe AS soils for any purpose will increase the leaching of acidity.

Laboratory Study of Methane Flux from Acid Sulphate Soil in South Kalimantan

Addition of organic matter in waterlogged conditions will enhance methanogenesis process that produces greenhouse gases. Fresh organic material is considered reactive because it contains carbons that is subject to decompose, therefore, when it exposed to acid sulphate soil, both in natural condition (aeration required) and intensive (aeration not required) will lower the value of redox potential. This experiment aimed to determine the flux of methane (CH4) from various locally available organic materials applied to acid sulphate soil. The experiment was arranged in factorial design with two factors. The first factor was the source of organic matter, i.e. fresh rice straw, fresh purun, fresh cattle manure, composted rice straw, composted purun and composted cattle manure, and control. The second factor was the management of organic matter i.e. placed on the soil surface with no tillage and mixed with soil during tillage. The results showed that application of fresh organic matter into inundated acid sulphate soil increased CH4 fluxes up to 23.78 µg CH4 g1 d1 which was higher than from composted organic matter (4.327 µg CH4.g1.d1). Methane flux due to organic matter management was significantly negatively (p=0.001) correlated with soil redox potential (Eh) with R2 of - 0.76. Organic matter placed on the soil surface with no tillage produced methane flux ranged from 0.33 to 20.78 g CH4 g1 d1, which was lower than methane flux produced from organic matter mixed with soil during tillage (0.38 to 27.27 g CH4 g1 d1). Composting organic matter before application and mixing them with the soil through tillage are highly recommended to reduce greenhouse gas emissions from cultivated acid sulphate soils.

The role of changing climate in driving the shift from perennial grasses to annual succulents in a Mediterranean saltmarsh

Summary Changing climate threatens the structure and function of saltmarshes, which are often severely degraded by other human perturbations. Along the Mediterranean coastline, increasing temperature and decreasing rainfall have been hypothesised to trigger habitat shifts from perennial grasses to annual succulents in fragile saltmarsh ecosystems, such as those fringing the North Adriatic coastline. We used manipulative field experiments to investigate the effects of increased temperature, decreased precipitation and increased inundation period associated with rising sea levels on the dominant species in the lower marsh, the perennial grass Spartina spp. and the annual succulent Salicornia veneta. At ambient inundation, the combined effects of increased temperature and decreased precipitation enhanced soil temperature and decreased soil moisture, resulting in an increased number of plants, height and live biomass of S. veneta, as well as greater dead biomass of Spartina spp. compared with current conditions. Increased inundation reduced the soil redox potential, and resulted in losses of both Spartina spp. and S. veneta, but these negative effects were much more pronounced for S. veneta. An inundation tolerance test confirmed that S. veneta is significantly more vulnerable to rapid increases in inundation than Spartina spp. We conclude that at current inundation, the increasing drought conditions in the North Adriatic Sea are favouring the spread of the annual succulent S. veneta. The increasing spread of these succulents could reduce the future capability of the system to respond to projected increasing sea levels, as S. veneta is highly vulnerable to increased inundation. Synthesis. Our results highlight the complex interactions between different components of changing climate. Management strategies for saltmarshes in the Mediterranean and other microtidal locations facing similar changes in climate should focus on maintaining the freshwater and coastal channels free from blockages to ameliorate the effects of episodic drought/heatwave conditions and increasing the sediment supply and preventing coastal squeeze to enhance the resilience of the system to the continuous threat of sea level rise.

Insights from “The Hidden Half”: The impact of root-zone oxygen and redox dynamics on the response of avocado to long-term irrigation with treated wastewater in clayey soil

Treated wastewater (TWW) is a major source of water for agriculture in Israel; however, recent reports indicate a marked yield loss in TWW-irrigated avocado and citrus orchards planted in clayey soils. The association of the yield loss with clayey soils rather than sandy soils suggests that it is associated with conditions in the root zone, and specifically poor aeration. A three-year study (2012–2015) was conducted in an avocado orchard planted in clayey soil, comparing the oxygen and redox conditions in the root zone of TWW-irrigated plots with fresh water (FW)-irrigated plots, together with the physiological status of the trees. Soil parameters included: continuous in-situ measurement of soil-water tension (SWT), soil oxygen, and soil redox potential, and periodic measurements of soil solution composition. Physiological parameters included: mineral composition of plant tissue from the leaves, trunk xylem and roots, root growth, yield, fruit setting, plant volume, and yield. TWW-irrigated plots were found to endure longer periods of low SWT indicating higher water content, accompanied by lower oxygen levels and more reduced conditions in comparison to FW-irrigated plots. The differences in these soil parameters between treatments were greater during the irrigation season than during the rainy period. The more reduced conditions in the TWW plots did not lead to significant differences in Fe or Mn concentrations in the soil solution or in plant leaves. TWW soil solution had significantly higher Na levels compared with FW. This did not affect the leaf Na content, but was expressed in substantially higher Na content in the root and trunk xylem, with up to seven times more trunk xylem Na in TWW-irrigated plants compared with FW-irrigated plants. Root growth was significantly hindered in TWW-irrigated plots compared with FW-irrigated plots. A negative correlation was found between root growth and the duration of hypoxic conditions, and similarly between root growth and the Na levels in the roots. TWW-irrigated plants had greater fruitlet numbers at the initial fruit-setting stage, but had a smaller number of fruit and a lower yield at harvest. The yield (kg/tree) negatively correlated with the duration of hypoxic conditions in the root zone but not with the Na levels in the roots or xylem. Our findings point towards a substantial role of oxygen deprivation as a major factor leading to the damage to TWW-irrigated orchards in clayey soils. Based on the assimilation of data, we suggest that a downward cascade is instigated in the TWW-irrigated orchards by increased input of Na into the soil, leading to degradation of soil hydraulic properties and reduced aeration. Impaired physiological functioning of the roots due to limited oxygen supply results in less roots growth, lower water uptake and impaired selectivity against Na uptake, thus imposing a negative feedback to increase soil water content, reduce aeration and root-zone oxygen availability for the roots, and further impair plant resistance to the high Na levels.

Soil greenhouse gas emissions from agroforestry and other land uses under different moisture regimes in lower Missouri River Floodplain soils: a laboratory approach

Changes in land use management practices may have multiple effects on microclimate and soil properties that affect soil greenhouse gas (GHG) emissions. Soil surface GHG emissions need to be better quantified in order to assess the total environmental costs of current and possible alternative land uses in the Missouri River Floodplain (MRF). The objective of this study was to evaluate soil GHG emissions (CO2, CH4, N2O) in MRF soils under long-term agroforestry (AF), row-crop agriculture (AG) and riparian forest (FOR) systems in response to differences in soil water content, land use, and N fertilizer inputs. Intact soil cores were obtained from all three land use systems and incubated under constant temperature conditions for a period of 94 days using randomized complete block design with three replications. Cores were subjected to three different water regimes: flooded (FLD), optimal for CO2 efflux (OPT), and fluctuating. Additional N fertilizer treatments for the AG and AF land uses were included during the incubation and designated as AG-N and AF-N, respectively. Soil CO2 and N2O emissions were affected by the land use systems and soil moisture regimes. The AF land use resulted in significantly lower cumulative soil CO2 and N2O emissions than FOR soils under the OPT water regime. Nitrogen application to AG and AF did not increase cumulative soil CO2 emissions. FLD resulted in the highest soil N2O and CH4 emissions, but did not cause any increases in soil cumulative CO2 emissions compared to OPT water regime conditions. Cumulative soil CO2 and N2O emissions were positively correlated with soil pH. Soil cumulative soil CH4 emissions were only affected by water regimes and strongly correlated with soil redox potential.

A survey of element toxicities in wheat grown in naturally waterlogged farmer's sodic fields of eastern Uttar Pradesh, India

ABSTRACTThis survey examined the element toxicities in wheat grown in naturally waterlogged farmer's sodic fields. Seven sites located in three districts (Faizabad, Pratapgarh, and Ambedkar Nagar) of eastern Uttar Pradesh, India were selected for the study. The data on soil redox potential (Eh), soil pH, soil electrical conductivity (EC), waterlogging duration, and crop age during waterlogging were recorded at the time of plant sampling in all the sites. Waterlogging caused a reduction of 21% to 65% in shoot dry weight in the survey sites. During waterlogging, the concentrations of iron (Fe), aluminum (Al), and sodium (Na) in leaves increased dramatically; the values of these elements were many folds higher than their reported critical toxicity levels (Fe-100 ppm, Al-50 ppm, and Na-8000 ppm, respectively). The results support the hypothesis that element toxicities occur during waterlogging in wheat grown in farmer's sodic field and identified Fe, Al, and Na toxicities as a major constraint for wheat production in the study area.

Anaerobic soil disinfestation impact on soil nutrients dynamics and nitrous oxide emissions in fresh-market tomato

Anaerobic soil disinfestation (ASD) is proposed as a pre-plant, non-chemical soil disinfestation technique to control several soilborne phytosanitary issues. Limited information is available on the impact of ASD on soil fertility, plant growth, and potential nutrient loss. The objectives of the current study were to evaluate the effects of ASD applied using composted poultry litter (CPL) and molasses as amendments, on soil redox potential, pH, temperature, soil nutrient content, plant biomass and nutrient accumulation, and nitrous oxide (N2O) emissions. A field study was conducted on fresh-market tomato (Solanum lycopersicum L.) at two sites, Immokalee and Citra, FL, comparing ASD applied using a mix of CPL at the rate of 22Mgha−1 and two rates of molasses [13.9 (ASD1) and 27.7m3ha−1 (ASD2)] as a carbon-source to chemical soil fumigation (CSF). ASD treatment had a significant impact on soil redox potential, but did not affect soil pH or temperature. Soil treatment did not affect nitrous oxide emissions from intact polyethylene mulched beds at either location. Emissions ranged from 0 to 0.378μgm−2h−1 and from 8.8 to 39.8μgm−2h−1 in Immokalee and Citra, respectively. However, on day 21 after punching holes in the polyethylene film to transplant, N2O emissions ranged from 1.56 to 4.83 and from 303.4 to 1480.1μgm−2h−1 in Immokalee and Citra, respectively. Emissions were higher in ASD than in CSF plots in Citra, but not in Immokalee. Molasses and CPL used in ASD treatments increased soil nutrients content, and particularly the availability of P and K. Results show no clear evidence of an increased risk of N loss with ASD compared to CSF. However, pre- and post-planting nutrient management should be adjusted to take into account the nutrients provided through the molasses and CLP application.

IRON DYNAMICS AND ITS RELATION TO SOIL REDOX POTENTIAL AND PLANT GROWTH IN ACID SULPHATE SOIL OF SOUTH KALIMANTAN, INDONESIA

&lt;p&gt;Organic matter has a function to maintain reductive conditions and to chelate toxic elements in acid sulphate soils. The study aimed to assess the dynamics of ferrous iron (Fe2+) in acid sulphate soil and its correlation with soil redox potential (Eh) and plant growth. The experiment was arranged in two factorial randomized block design with three replications. The first factor was two types of organic matter: (1) control (without organic matter), (2) rice straw and (3) rush weed (Eleocharis dulcis). The second factor was time of decomposition of organic matter: I1 = 2 weeks, I2 = 4 weeks, I3 = 8 weeks, and I4 = 12 weeks (farmer practice). The results showed that concentration of ferrous iron in the soil ranged from 782 to 1308 mg kg-1 during the rice growing season. The highest constant rate of iron reduction (k F2+) was observed on application of rice straw and rush weed with decomposition time of 8 weeks with the k Fe2+ value of 0.016 and 0.011 per day, respectively, while the ferrous iron formation without organic matter had the k Fe2+ value of 0.077 per day. The ferric iron (Fe3+) reduction served as a function of soil Eh as indicated by the negative correlation of ferrous iron and Eh (r = -0.856*). Organic matter decreased exchangeable iron due to chelating reaction. Iron concentration in roots was negatively correlated with soil soluble iron (r = -0.62*). Application of rice straw decomposed for 8 weeks increased the height of rice plant up to 105.67 cm. The score of Fe2+ toxicity at 8 weeks after planting ranged from 2 to 3, so rice crop did not show iron toxicity symptoms. &lt;/p&gt;

Effects of screenhouse cultivation and organic materials incorporation on global warming potential in rice fields.

Global rice production will be increasingly challenged by providing healthy food for a growing population at minimal environmental cost. In this study, a 2-year field experiment was conducted to investigate the effects of a novel rice cultivation mode (screenhouse cultivation, SHC) and organic material (OM) incorporation (wheat straw and wheat straw-based biogas residue) on methane (CH4) and nitrous oxide (N2O) emissions and rice yields. In addition, the environmental factors and soil properties were also determined. Relative to the traditional open-field cultivation (OFC), SHC decreased the CH4 and N2O emissions by 6.58-18.73 and 2.51-21.35%, respectively, and the global warming potential (GWP) was reduced by 6.49-18.65%. This trend was mainly because of lower soil temperature and higher soil redox potential in SHC. Although the rice grain yield for SHC were reduced by 2.51-4.98% compared to the OFC, the CH4 emissions and GWP per unit of grain yield (yield-scaled CH4 emissions and GWP) under SHC were declined. Compared to use of inorganic fertilizer only (IN), combining inorganic fertilizer with wheat straw (WS) or wheat straw-based biogas residue (BR) improved rice grain yield by 2.12-4.10 and 4.68-5.89%, respectively. However, OM incorporation enhanced CH4 emissions and GWP, leading to higher yield-scaled CH4 emissions and GWP in WS treatment. Due to rice yield that is relatively high, there was no obvious effect of BR treatment on them. These findings suggest that apparent environmental benefit can be realized by applying SHC and fermenting straw aerobically before its incorporation.

Effect of Elevation on Soil Properties in Reconstructed Back Barrier Island Coastal Marsh Using Dredged Materials

Soil physical, chemical and bio-geochemical properties of a back barrier island coastal marsh restored by low pressure hydraulic dredging were monitored and analyzed from 2005 to 2009. A 109 ha restored marsh located at Port Fourchon, Louisiana, was divided into five habitats based on elevation. The habitats were classified as high (knoll), flat (swale), upper intertidal, intertidal and open water (submerged soils). The higher habitats were created nearer the dredged material source by deposited dredged coarser sediment mainly sand and oyster shells in mounds. Material with higher clay and silt content in the slurry were found in the habitats located at greater distances from the dredged material source. Soil elemental contents were statistically significantly different among habitats. Soil redox potential was also significantly different among habitats with the higher elevations having more oxidized redox values. Soil elevation was a strong influence on soil physical and chemical properties for several years post construction. Uneven distribution of dredged materials during the construction phase resulted in distinct variation in elevation and soil properties and the conclusion was that marsh creation would be more effective if dredged materials were uniformly distributed.

Effects of increased temperatures and rice straw incorporation on methane and nitrous oxide emissions in a greenhouse experiment with rice

We investigated the effect of increased temperatures of water and soil, together with the incorporation of rice straw, on emissions of methane (CH4) and nitrous oxide (N2O), and the daily variation in CH4 emissions. Three temperature treatments (floodwater temperature), ambient, ambient +2°C and ambient +4°C, and two amounts of rice straw (0 and 6 t ha−1) were arranged in a randomized complete block design with four replications. The emissions of CH4 and N2O and the soil's redox potential (Eh) were measured weekly for two crop cycles. Daily variation in CH4 emission rates was measured with and without rice straw incorporation in planted and unplanted soil (with no warming treatments) during four growth stages of the crop. Methane emissions increased by as much as 91% with increasing amounts of water and soil temperature (+2 and +4°C), up to 34–35°C. Increases in temperature (+2 and +4°C above ambient) above 34–35°C decreased emissions by 30–36%. A decrease in soil Eh to &lt; −100 mV and in CH4 emissions was observed earlier in the pots containing rice straw than in those without straw. Methane emissions varied daily; they were larger from 11:00 to 14:00 hours, particularly in unplanted soil. They showed positive correlations with the temperatures of both soil and air. In contrast, N2O emissions were negligible throughout the growing season. The emissions of CH4 evidently depend on the background temperature range; in our experiment, CH4 emissions increased up to 34°C and then they decreased above that.Highlights:GHG emissions were measured from flooded rice soil under elevated temperatures. Temperature, straw incorporation and rice plants affected daily variation in methane emissions. An increase in temperature increased methane emission by up to 91%. Increased temperature decreased methane emissions when background temperature was above 34–35°C.

Intermittent drainage in paddy soil: ecosystem carbon budget and global warming potential

Intermittent drainage of rice fields alters soil redox potential and contributes to the reduction of CH4 emission and thus may reduce net global warming potential (GWP) during rice cultivation. Incorporation of green biomass helps maintaining soil organic matter, but may increase CH4 emission. We investigated net ecosystem carbon budget (NECB) and net GWP under two water management regimes—continuous flooding and intermittent drainage—having four biomass incorporation levels (0, 3, 6 and 12 Mg ha−1). Water management and biomass incorporation level demonstrated significant (P < 0.05) interaction effect on the NECB and GWP. Intermittent drainage decreased the NECB by ca. 6–46 % than continuous flooding under same rates of cover crop biomass (CCB) incorporation. Moreover, intermittent drainage reduced seasonal CH4–C fluxes by ca. 54–58 % and net GWP by 35–58 % compared to continuous flooding. There was also no significant reduction in rice yield because of intermittent drainage under similar CCB. This implies that incorporation of 3 Mg ha−1 CCB and intermittent drainage could be a good option for reducing net GWP and higher grain yield.

Integrated rice-duck farming mitigates the global warming potential in rice season

Integrated rice-duck farming (IRDF), as a mode of ecological agriculture, is an important way to realize sustainable development of agriculture. A 2-year split-plot field experiment was performed to evaluate the effects of IRDF on methane (CH4) and nitrous oxide (N2O) emissions and its ecological mechanism in rice season. This experiment was conducted with two rice farming systems (FS) of IRDF and conventional farming (CF) under four paddy-upland rotation systems (PUR): rice-fallow (RF), annual straw incorporating in rice–wheat rotation system (RWS), annual straw-based biogas residues incorporating in rice–wheat rotation system (RWB), and rice-green manure (RGM). During the rice growing seasons, IRDF decreased the CH4 emission by 8.80–16.68%, while increased the N2O emission by 4.23–15.20%, when compared to CF. Given that CH4 emission contributed to 85.83–96.22% of global warming potential (GWP), the strong reduction in CH4 emission led to a significantly lower GWP of IRDF as compared to CF. The reason for this trend was because IRDF has significant effect on dissolved oxygen (DO) and soil redox potential (Eh), which were two pivotal factors for CH4 and N2O emissions in this study. The IRDF not only mitigates the GWP, but also increases the rice yield by 0.76–2.43% compared to CF. Moreover, compared to RWS system, RF, RWB and RGM systems significantly reduced CH4 emission by 50.17%, 44.89% and 39.51%, respectively, while increased N2O emission by 10.58%, 14.60% and 23.90%, respectively. And RWS system had the highest GWP. These findings suggest that mitigating GWP and improving rice yield could be simultaneously achieved by the IRDF, and employing suitable PUR would benefit for relieving greenhouse effect.

Biogeochemical modeling of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; production in anoxic Arctic soil microcosms

Abstract. Soil organic carbon turnover to CO2 and CH4 is sensitive to soil redox potential and pH conditions. However, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximately describe the observed pH evolution without additional parameterization. Although Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. The equilibrium speciation predicts a substantial increase in CO2 solubility as pH increases, and taking into account CO2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO2 production from closed microcosms can be substantially underestimated based on headspace CO2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.