Soil Redox Potential Research Articles

Greenhouse Gas Emissions from a Created Brackish Marsh in Eastern North Carolina

Tidal marsh creation helps remediate global warming because tidal wetlands are especially proficient at sequestering carbon (C) in soils. However, greenhouse gas (GHG) losses can offset the climatic benefits gained from C storage depending on how these tidal marshes are constructed and managed. This study attempts to determine the GHG emissions from a 4–6 year old created brackish marsh, what environmental factors governed these emissions, and how the magnitude of the fluxes relates to other wetland ecosystems. The static flux chamber method was used to measure GHG fluxes across three distinct plant zones segregated by elevation. The major of soil GHG fluxes from the marsh were from CO2 (−48–192 mg C m-2 h-1), although it was near the lower end of values reported from other wetland types having lower salinities, and would mostly be offset by photosynthetic uptake in this created brackish marsh. Methane flux was also low (−0.33–0.86 mg C m-2 h-1), likely inhibited by the high soil SO4 2− and soil redox potentials poised above −150 mV in this in this created brackish marsh environment. Low N2O flux (−0.11–0.10 mg N m-2 h-1) was due to low soil NO3 − and soil redox conditions favoring complete denitrification. GHG fluxes from this created brackish marsh were generally lower than those recorded from natural marshes, suggesting that C sequestration may not be offset by the radiative forcing from soil GHG emissions if projects are designed properly.

Effect of Compost Combination on Methane Emission in Undisturbed Acid Sulphate soil in South Kalimantan of Indonesia

A greenhouse experiment was conducted to examine the cumulative methane (CH4) emission in paddy soils and correlation with soil redox potential (Eh), soil pH and plant growth. The experiment was arranged in two factorial randomized block designs with three replications. The first factor was a kind of of organic matter, i.e. without organic matter (T0), combination of 50% of composted straws and 50% composted rush weed (T1), combination of 30% of composted straws and 30% composted rush weed and 40% composted cattle manure (T2) and the second factor was the management of water that was continuously flooded and leaching. The methane emission was measured in South Kalimantan using the chamber and gas chromatogram technique. The results showed methane emission in undisturbed acid sulphate soil ranged from 0.05 to 0.32 mg CH4.m-2.minute-1 during the rice-growing season. The methane emission from the paddy soil were lower when the paddy was drained than when it was flooded. Correlation analysis showed a negative relation between methane emission and soil redox potential (Eh) and soil pH in both water management. The rice plant height and number of buds has positively correlation with methane emission with coeffecient correlation of r=0.84**(P<0.0001) and r=0.64**(P=0.004), respectively. Normal 0 false false false IN X-NONE X-NONE [ How to Cite : Wahida A and A Maas. 2015. Effect of Compost Combination on Methane Emission in Undisturbed Acid Sulphate soil in South Kalimantan of Indonesia. J Trop Soils 20: 135-141. Doi: 10.5400/jts.2015.20.3.135 ]

Emissions of Methane and Nitrous Oxide from Rainfed Rice Field Treated with Different Rice Planting Systems and Nematicide Applications at Central Java, Indonesia

Rice field is issued as a source of greenhouses gases (GHGs) emissions especially methane (CH4) and nitrous oxide (N2O). Rice cultural approach could mitigate GHGs emissions i.e. through rice planting systems and nematicide application. The field experiment was conducted in rainfed rice field at Pati District, Central Java to determine effect of planting systems and nematicide application on emissions of methane and nitrous oxide from rainfed rice field. The six treatments were arranged in a randomized block design with three replicates, namely transplanted rice (TR) without applying nematicide, TR + neem cake, TR + carbofuran, direct seeded rice (DSR) without applying nematicide, DSR + neem cake, DSR + carbofuran. Parameters observed were methane flux, nitrous oxide flux, organic C content in rhizosphere, soil pH, soil redox potential surrounding rhizosphere of Ciherang variety. Methane emission under transplanted rice system was generally higher than direct seeded rice system. The treatment of DSR + neem cake resulted lowest methane emission (71 kg CH4 ha-1 season-1). The TR system emitted N2O lower significantly than the DSR system. Application of nematicide inhibitor materials decreased more effectively N2O emission. The DSR system increased significantly grain yield and N uptake, while application of nematicide materials didn’t increase grain yield but increased significantly N uptake. Normal 0 false false false IN X-NONE X-NONE [ How to Cite : Anicetus W and ES Harsanti. 2015. Emissions of Methane and Nitrous Oxide from Rainfed Rice Field Treated with Different Rice Planting Systems and Nematicide Applications at Central Java, Indonesia. J Trop Soils 20: 127-134. Doi: 10.5400/jts.2015.20.3.127 ]

Nitrification Inhibitors: A Perspective tool to Mitigate Greenhouse Gas Emission from Rice Soils

Rice fields are significant contributors of greenhouse gases mainly methane and nitrous oxide to the atmosphere. Increasing concentrations of these greenhouse gases play significant role in changing atmospheric chemistry such as mean air temperature, rainfall pattern, drought, and flood frequency. Mitigation of greenhouse gases for achieving sustainable agriculture without affecting economical production is one the biggest challenge of twenty first century at national and global scale. On the basis of published scientific studies, we hereby assess the use of nitrification inhibitors for greenhouse gas mitigation from rice soil. Biologically oxidation of ammonium to nitrate is termed as nitrification and materials which suppress this process are known as nitrification inhibitors. Soil amendment by addition of certain nitrification inhibitors such as neem oil coated urea, nimin-coated urea; dicyandiamide, encapsulated calcium carbide, and hydroquinone reduce cumulative methane and nitrous oxide emission from rice. Firstly, these inhibitors reduce nitrous oxide emissions both directly by nitrification (by reducing NH4+ to NO3-) as well as indirectly by de-nitrification (by reducing NO3- availability in soil). Secondly, methane emission from rice soil can be reduced by enhancing methane oxidation and suppressing methane production and further by reducing the aerenchymal transportation through rice plant. Application of some of the nitrification inhibitors such as calcium carbide and encapsulated calcium carbide reduce methane production by releasing acetylene gas which helps in reducing the population of methanogenic microbes in the soil. Application of nitrification inhibitors also helps to maintain soil redox potential at higher level subsequently reducing cumulative methane emission from soil. Plant derived organic nitrification inhibitors (neem oil, neem cake, karanja seed extract) are eco-friendly and possess substantial greenhouse gas mitigation potential from rice. In the current scenario of global warming and environmental pollution, application of organic plant derived nitrification inhibitors is much needed for sustainable agriculture.

In‐situ transformation of iron‐bearing minerals in marshland‐derived paddy subsoil

Transformations of Fe‐bearing minerals under alternating redox conditions are not fully understood. In‐situ approaches under field conditions have rarely been used. We exposed mesh bags containing ferrihydrite, goethite or nontronite to changing redox conditions in subsoil that had been under paddy management for 100, 700 and 2000 years. After 12 months, the minerals were retrieved and analysed for organic carbon and by X‐ray diffraction; in addition, nontronite was analysed for cation exchange capacity and by Mössbauer spectroscopy at 278 and 4.2 K. Field exposure of the test minerals was complemented by measurements of soil redox potential and analyses of soil water. Minerals accumulated little organic carbon because of high pH and salinity. Goethite samples showed no changes in X‐ray diffraction patterns; therefore, they did not undergo detectable transformation, despite redox potentials frequently around −200 mV. Ferrihydrite transformed into more crystalline oxides, such as lepidocrocite, goethite and haematite. The extent of transformation, presumably by Fe2+‐catalysed recrystallization, increased with the time the soil had been under paddy management. Nontronite samples showed striking changes in surface colour, but no changes in X‐ray diffraction patterns or in cation exchange capacity. However, Mössbauer spectroscopy gave clear indications of irreversible changes within the nontronite crystal structure. Such changes have so far been observed only with chemical reduction, but it seems that they can occur under natural conditions. The results show that the overall redox status of a soil (i.e. the number of redox cycles it has undergone before) governs the extent and direction of mineral transformations during following redox cycles.HighlightsHow do ferrihydrite, goethite and nontronite transform under strongly alternating redox conditions? In‐situ exposure of minerals in soil under paddy management for 100, 700 and 2000 years. Fe2+‐catalysed ferrihydrite transformation; irreversible changes in nontronite crystal structure. The number of redox cycles a soil undergoes, governs mineral transformations in later redox cycles.

The Effects of Fiddler Crabs (Uca sp) on C/N Ratio and Redox Potential of Soil in Mangrove Ecosystems

Research has been done in Ketapang mangrove area of Probolinggo city in months of September-November 2015. The objectives are to observe the fiddler crab community stucture and to analyze the effects of fiddler crabs on C/N ratio and redox potential of soil in mangrove ecosystems. The samples of fiddler crabs were taken during the low tides at 4 station (20 transects with sizes of 1 m 2 ). Data of the fiddler crabs were measured from the soil digging insides the transect. The soil samples were taken from these crab holes wall (at the surface and at the depth of 20 cm), under the holes at the depth of 40 cm as well as from the locations that undwells by these animals at the same depth. The fiddler crab identified are U. Triangularis between 2 – 6 ind/m 2 , U paradussumieri 1 – 3 ind/m 2 , U perplexa 14 – 32 ind/m 2 , U dussumieri 12 – 27 ind/m 2 and U. Tetragonon 3 – 6 ind/m 2 . The diversity is moderate (H = 1.7) and the dominance index was low (C = 0.37). C/N ratio soil were inhabited by fiddler crab between 6 – 14, the undwelled area were 14 – 20. Soil C/N ratio was inhabited by the fiddler crab at the surface and depth of 20 cm in average of 9 cm while at 40 cm in avergae of 12. The low of C/N ratio at surface and depth of 20 cm causing the organic matter turnover faster because the high nitorgen content. Soil potential redox (Eh) the undwelled areas was found –0.647 mV, meanwhile the soil Eh in the dwelled areas was positive (0.68 till 0.87 mV). This mean, the decpmposition was occured during aerobic condition and will produce untoxic subtances.

Soil structure amelioration with quicklime and irrigation experiments in earth graves

Air supply and soil moisture have significant impact on the decay time necessary for complete decomposition of an interred body. Concerning the general structure and hydraulic as well as pneumatic conditions, in many cases, a permeable refilled soil material surrounded by the undisturbed and less permeable soil outside the grave results in water ponding, less aerated conditions, and lower redox potential values within the grave. This reduces the decomposition speed or even leads to preservation of the entire body. In order to ascertain soil structural processes and hydraulic properties in an earth grave within the first year after burial, a monitoring of soil redox and matric potentials was realized in newly refilled artificial (empty) graves. We surveyed four variations: undisturbed reference soil, soil backfill in artificial grave, soil backfill in artificial grave amended with 20 kg CaO m−3, and grave base and walls strewed with CaO. In the fourth artificial grave (soil backfill only), irrigation experiments were conducted in order to simulate the effects of grave maintenance on soil water budget. Pore size distribution, air conductivity, and saturated hydraulic conductivity were measured on soil core samples from the variations. The monitoring was realized with redox sensors and tensiometers in 50- and 130-cm depth in all four variations. Soil structure disruption increased soil porosity but also favored saturation of the soil in context with precipitation events. Compared with the graves without amendment, the addition of quicklime resulted in higher air capacity and air permeability, saturated hydraulic conductivity, and a better-aerated (higher redox potentials) and less water-saturated soil. Non-recurring irrigation with 2.2, 4.4, and 8.9 mm did not affect the soil moisture in the 50- and 130-cm depth. Repeated irrigation with 8.9 mm on consecutive days led to persistent water saturation in the soil, especially in the 130-cm depth. The disturbed soil structure in the cover layer of an earth grave is sensitive to settlement and, together with a tendency to the development of stagnic conditions, this can have negative impact on soil aeration in the grave. Addition of quicklime to the soil enhances crack development in the base and walls of the grave, stabilizes the soil fragments in the backfill, and prevents intensive settlement processes. This reduces water ponding and leads to a better aeration of the soil. Irrigation of earth graves should be reduced to a minimum.

Richness, biomass, and nutrient content of a wetland macrophyte community affect soil nitrogen cycling in a diversity-ecosystem functioning experiment

The development of soil nitrogen (N) cycling in created wetlands promotes the maturation of multiple biogeochemical cycles necessary for ecosystem functioning. This development proceeds from gradual changes in soil physicochemical properties and influential characteristics of the plant community, such as competitive behavior, phenology, productivity, and nutrient composition. In the context of a 2-year diversity experiment in freshwater mesocosms (0, 1, 2, 3, or 4 richness levels), we assessed the direct and indirect impacts of three plant community characteristics – species richness, total biomass, and tissue N concentration – on three processes in the soil N cycle – soil net ammonification, net nitrification, and denitrification potentials. Species richness had a positive effect on net ammonification potential (NAP) through higher redox potentials and likely faster microbial respiration. All NAP rates were negative, however, due to immobilization and high rates of ammonium removal. Net nitrification was inhibited at higher species richness without mediation from the measured soil properties. Higher species richness also inhibited denitrification potential through increased redox potential and decreased nitrification. Both lower biomass and/or higher tissue ratios of carbon to nitrogen, characteristics indicative of the two annual plants, were shown to have stimulatory effects on all three soil N processes. The two mediating physicochemical links between the young macrophyte community and microbial N processes were soil redox potential and temperature. Our results suggest that early-successional annual plant communities play an important role in the development of ecosystem N multifunctionality in newly created wetland soils.

Research and Monitoring on Conservation State and Preservation Conditions in Unsaturated Archaeological Deposits of a Medieval Farm Mound in Troms and a Late Stone Age Midden in Finnmark, Northern Norway

This paper presents archaeological observations and results of palaeoecological and geo-chemical analyses of archaeological deposits from two rural sites in northernmost Norway. These are combined with climate data and the first period of continuous monitoring of soil temperature, moisture, and redox potential in sections. This data constitutes the basic research material for evaluations of conservation state and preservation conditions. The data has been collected in collaboration with the partners of a cross-disciplinary project: ‘Archaeological Deposits in a Changing Climate. In situ Preservation of Farm Mounds in Northern Norway’ funded by the Norwegian Council for Research (http://www.niku.no/en/archaeology/environmental_monitoring/archaeological_deposits_in_a_changing_climate_in_situ_preservation_of_farm_mounds/). This is an important Norwegian research initiative on monitoring of rural archaeological deposits, and the results have consequences for heritage management of a large number of sites from all periods. Palaeoecological analyses and redox measurements have revealed ongoing decay that might not otherwise have been detected. Decay studies indicate that both site types may be at risk with the predicted climate change. Some mitigating acts are suggested.

Phosphorus Release to Floodwater from Calcareous Surface Soils and Their Corresponding Subsurface Soils under Anaerobic Conditions.

Enhanced phosphorus (P) release from soils to overlying water under flooded, anaerobic conditions has been well documented for noncalcareous and surface soils, but little information is available for calcareous and subsurface soils. We compared the magnitude of P released from 12 calcareous surface soils and corresponding subsurface soils to overlying water under flooded, anaerobic conditions and examined the reasons for the differences. Surface (0-15 cm) and subsurface (15-30 cm) soils were packed into vessels and flooded for 8 wk. Soil redox potential and concentrations of dissolved reactive phosphorus (DRP) and total dissolved Ca, Mg, Fe, and Mn in floodwater and pore water were measured weekly. Soil test P was significantly smaller in subsurface soils than in corresponding surface soils; thus, the P release to floodwater from subsurface soils was significantly less than from corresponding surface soils. Under anaerobic conditions, floodwater DRP concentration significantly increased in >80% of calcareous surface soils and in about 40% of subsurface soils. The increase in floodwater DRP concentration was 2- to 17-fold in surface soils but only 4- to 7-fold in subsurface soils. With time of flooding, molar ratios of Ca/P and Mg/P in floodwater increased, whereas Fe/P and Mn/P decreased, suggesting that resorption and/or reprecipitation of P took place involving Fe and Mn. Results indicate that P release to floodwater under anaerobic conditions was enhanced in most calcareous soils. Surface and subsurface calcareous soils in general behaved similarly in releasing P under flooded, anaerobic conditions, with concentrations released mainly governed by initial soil P concentrations.

Time‐Course Changes in Speciation and Solubility of Cadmium in Reduced and Oxidized Paddy Soils

Core Ideas The formation and dissolution of CdS were investigated in low‐ and high‐S soils. CdS reached 90% in the high‐S soil but did not exceed 35% in the low‐S soil. Cd dissolved rapidly at soil Eh &gt;435 mV (low‐S soil) and &gt;529 mV (high‐S soil). A prolonged flooding during rice (Oryza sativa L.) cultivation is recommended to immobilize soil Cd by the formation of CdS under anoxic conditions. The problem with this recommended practice is that it reduces rice yields compared with intermittent flooding, which is less effective at immobilizing CdS through reductive precipitation. This study investigated the solubility of Cd in relation to chemical speciation of Cd and S and soil redox potential through a time series of measurements during a 29‐d reduction period followed by a 20‐d oxidation period using X‐ray absorption fine structure spectroscopy and chemical extraction. Two Aquent soils with different S levels in water‐ and oxalate‐extractable fractions (hereafter low‐S and high‐S soils) were used to investigate the formation and dissolution of CdS. In the reducing period, the CdS proportion in the high‐S soil rapidly increased to 30% at Day 4 and reached 90% at Day 29, whereas CdS in the low‐S soil did not exceed 35%. In the following oxidizing period, CdS in the soils underwent oxidative dissolution but was not completely dissolved, remaining at &lt;20% of the total Cd. A two‐piece segmented linear relationship existed between HCl‐extractable Cd and soil Eh, and the regression slope was 28‐fold greater for the low‐S soil at Eh &gt;435 mV and 38‐fold greater for the high‐S soil at Eh &gt;529 mV. This result indicates that each soil has a threshold Eh value at which the solubility of Cd is drastically altered during the course of soil reduction and oxidation processes.

Study of dynamics of electro-chemical properties of submerged soils

Wetland rice systems in Asia make a major contribution to global rice supply. The system is also able to maintain soil fertility on a sustainable basis. The essential components of wetland rice culture comprise cultivation of land in the flooding, puddling and transplanting of rice seedlings into puddled rice paddies, and growing the rice crop under flooding. The wetland rice system, growing rice in submerged soils has a great ameliorative effect on chemical fertility: largely by bringing pH in the neutral range, resulting in better availability of plant nutrients and accumulation of organic matter. Submergence bring a lot changes in redox potential which in turn gives the idea of reduction of nutrients to release to soil solution to make available to plant. This article revealed the dynamic changes of soil pH, electrical conductivity and Redox potential on submergence.

Soil chemical and microbial responses to biogas slurry amendment and its effect on Fusarium wilt suppression

The rapid development of biogas production will result in increased use of biogas slurry (BS) as organic fertilizer. However, side effects such as suppression of soilborne diseases are not yet well investigated and understood. Therefore, the objectives of the study were to evaluate the effects of biogas slurry application on suppression of Fusarium wilt disease of watermelon and its relationship with soil chemical and microbiological properties. Pot and field experiments were conducted to compare effects of biogas slurry application on Fusarium wilt disease suppression of watermelon in soil with a moisture content of 60% water holding capacity (WHC) or flooded continuously. Fusarium wilt was significantly suppressed in soil from biogas slurry amended plots. Biogas slurry flooding enhanced the degree of suppression in the pot experiment. Moreover, the biogas slurry treatment also significantly suppressed Fusarium wilt in the field with a disease index of 33.2% compared with 69.6% in water treatment. Biogas slurry strongly reduced the pathogen population in rhizosphere soil. The populations were decreased by 43.1% and 95.9% in the biogas slurry moist and flooding treatments, respectively. Biolog data indicated that average well color development (AWCD) and Shannon-weaver index were increased significantly in biogas flooding treatment. Principal component analysis showed that Fusarium wilt was negatively correlated with NH4+-N, available K (AK), water-soluble carbon (DOC), water soluble nitrogen (DON) and phenolic acid (PA) contents in soil and positively correlated to soil pH and soil redox potential (Eh). Microbial communities, in general, did not significantly correlate with disease suppression.

Soil solution chemical attributes, rice response and water use efficiency under different flood irrigation management methods

The water availability is the main limiting factor of global rice production under flood irrigation. In this context, water suppression during the rice growing cycle (intermittent irrigation) arises as an alternative to traditional continuous irrigation. However, the intermittent irrigation may affect the dynamics of soil solution chemical attributes, the water use and the rice yield. Thus, our study aims to evaluate the electrochemical characteristics and nutrient availability in soil solution during the growing cycle, the plant response and the water use efficiency of irrigated rice under different flood irrigation management methods. For this, a field experiment was conducted in Southern Brazil, with three treatments: 1) continuous irrigation; 2) one water suppression (between V6–V8); and 3) two water suppressions (between V6–V8 and V8–V10). Regarding soil solution electrochemistry, the pH and redox potential (EH) were affected by the water suppression, increasing and decreasing due to soil reoxidation, respectively. The electrical conductivity (EC) decreased during the rice growing cycle, accompanying the plant development. The nutrients (except the potassium) were affected by water suppression, diminishing their availability. However, when the water layer was reestablished, there were no differences on soil solution electrochemistry among the irrigation methods. Regarding rice response, no differences were observed and the amounts produced were, in average, 9.9 and 13.4Mgha−1 of grains and shoot dry matter, respectively. The same occurred for the water amount utilized and water use efficiency (WUE) and the values observed were, in average, 9094m3ha−1 and 1.1kgm−3, respectively. More studies regarding different flood irrigation management methods are necessary to encourage the adoption of intermittent irrigation by rice farmers of Southern Brazil and increase the sustainability of rice production.

Facultative grazing and bioturbation by macrodetritivores alter saltmarsh plant–plant interactions under stress

Summary The importance of positive plant–plant interactions is generally suggested to increase towards more stressful conditions, due to mutual stress amelioration between plants. Bioturbating macrodetritivores can also ameliorate stress through bioturbation, but can also become selective herbivores under food‐limited conditions, making the outcome of plant–plant interactions under stress in the presence of macrodetritivores unclear. We studied how combining environmental stress (waterlogging) with the presence of the soil macrodetritivore Orchestia gammarellus affected the outcome of the interaction between two salt marsh plants: the tall, late successional Elytrigia atherica and the shorter, early successional Festuca rubra. In a replacement design competition experiment under controlled conditions, we found that soil redox potential was negatively affected by waterlogging and positively affected by the presence of O. gammarellus. The survival and shoot biomass of E. atherica was not significantly affected by waterlogging or by the presence of bioturbators. The survival and shoot biomass of F. rubra was especially decreased when waterlogging was combined with the presence of O. gammarellus, as this macrodetritivore turned into a selective grazer on F. rubra under these conditions. We found that E. atherica produced double shoot biomass and F. rubra produced much less shoot biomass in their mixed cultures than was expected from the monocultures of same waterlogging/Orchestia treatments. Hence, the presence of the bioturbator strongly promoted the competitive advantage of E. atherica over F. rubra due to the combination of stress amelioration for the first species and selective herbivory on the second species. Synthesis. This study shows that the inclusion of bioturbating macrodetritivores complicates the standard prediction that plant–plant interactions become more positive towards more stressful conditions. A novel insight is that macrodetritivores can affect the structure and diversity of plant communities through multiple mechanisms. Under benign conditions bioturbating macrodetritivores ameliorated soil conditions, permitting co‐occurrence of competing plant species. At high environmental stress (waterlogging) macrodetritivores selectively graze higher quality plant species and emerging seedlings, thus promoting dominance of the lower quality species. Hence, the facultative feeding behaviour of macrodetritivores deserves further attention.

Influence of Microbial Composition on the Carbon Storage Capacity of the Mangrove Soil at the Land-ocean Boundary in the Sundarban Mangrove Ecosystem, India

ABSTRACTSpatiotemporal assessment of the mangrove soil of Indian Sundarban revealed that decomposition rate of the organic matter was significantly lower in the anoxic condition than that of the oxic condition. Higher degree of enzyme activity in the oxic soil than the anoxic condition suggested that slower biomineralization in anoxic condition would facilitate long-term storage of organic matter in that particular ecosystem. Microbial population of nitrifying bacteria, phosphate solubilizing bacteria, cellulose degrading bacteria and fungi showed significant reduction in anoxic incubation than that in oxic incubation. In contrary, sulfate reducing bacteria and free living N2 fixing bacteria showed higher population in anoxic incubation indicating their preference for anaerobic condition. Soil CO2 emission rate decreased with the increase in anoxicity and was largely dependent on the soil redox potential, organic carbon and microbial population of the mangrove soil.

Dissimilatory nitrate reduction to ammonium and N2O flux: effect of soil redox potential and N fertilization in loblolly pine forests

Nitrogen (N) fertilization and soil redox potential influence N cycling processes in forested ecosystems. Gross N transformations are indicators of NH4 + and NO3 − production and consumption within soil. Furthermore, dissimilatory nitrate reduction to ammonium (DNRA), a typically overlooked process in terrestrial N cycling, can conserve N within soil by reducing losses of soil N via NO3 − leaching and denitrification. We tested the effects of urea fertilization and soil redox on microbial N cycling processes and N2O fluxes using a 15N tracer experiment in soils from loblolly pine plantations located in different physiographical regions (i.e., Coastal Plain of North Carolina and Piedmont of Virginia). Mineral soils (0–15 cm) from fertilized and unfertilized plots were incubated at high (Eh, 200 to 400 mV) and low redox potential (Eh, −100 to 100 mV). Site differences were limited primarily to edaphic factors, although gross N mineralization was higher in NC. Gross nitrification, DNRA, and NO3–−–N concentrations were higher in soils from fertilized plots. DNRA was higher at high compared to low redox potential, while N2O fluxes were higher at low redox potential. Fluxes of N2O were further enhanced in fertilized treatments incubated at low redox potential. DNRA was positively correlated with NO3 − availability, but not to soil C pools. Furthermore, DNRA was negatively correlated with C/NO3 − ratio, implying that NO3 − pool size was the primary factor influencing DNRA. These results suggest N fertilization has alleviated limitations to nitrification, DNRA, and N2O production processes and that gaseous losses of N will prevail over N conservation pathways at low soil redox potentials.

Effect of synthetic amorphous and crystalline iron oxides on redox potential and exchangeable cations in wetland soils of Maputaland Kwazulu-Natal, South Africa

Some grey-coloured soils of the Maputaland Coastal Plains in northern KwaZulu-Natal do not exhibit the redox morphology normally associated with seasonal water saturation, resulting in serious limitations in using soil morphology for wetland delineation. One of the hypotheses to explain this phenomenon is that these soils simply do not contain enough iron minerals that can be reduced and re-oxidised to form redox accumulations and depletions. Alternatively, if iron minerals are present, they are too crystalline to be readily reduced as a result of the lower iron activity associated with these oxides and can only be reduced at a slow rate. This investigation aimed to determine if a deficiency in iron oxides could explain the absence of redoximorphic features in the wetland soils. A split-plot experimental design with 78 cores was set up to investigate the effect that varying iron crystallinity had on soil redox potential. The experiment was conducted in a controlled environment in the laboratory with the temperature set at 23°C with fluctuations of ±2°C. Synthetic ferrihydrite and goethite were mixed with soils (0.84 g.kg −1 ) and packed to a bulk density of 1.4 Mg m −3 . The cores were then saturated to 73% of porosity and the pH, Eh, Ca, Mg, Fe, and Mn measured bi-weekly. The ferrihydrite and goethite treatments did not affect ammonium acetate extractable Ca and Mg. The treatments did, however, increase significantly the ammonium acetate extractable Fe, Mn, and pH, while both treatments significantly decreased pe over the 42 day extraction period. The goethite treatment reduced within five days, while ferrihydrite only reduced after 20 days. The Fe o /Fe d ratios for the treatments suggested that ferrihydrite started as less crystalline and increased sharply after saturation, while the crystallinity of the goethite treatment only increased slightly. Results presented here indicate that the absence of redoximorphic features in the soils of Manguzi could be attributed to the low iron oxide content of the soils. Other indicators, such as vegetation or long-term water measurements, therefore need to be engaged to delineate wetlands in the soils of the Maputaland Coastal Plain.

Effect of By-Product Gypsum Fertilizer on Methane Gas Emissions and Rice Productivity in Paddy Field

Rice cultivation in paddy field affects the global balance of methane (CH₄) as a key greenhouse gas. To evaluate a potential use of by-product gypsum fertilizer (BGF) in reducing CH₄ emission from paddy soil, CH₄ fluxes from a paddy soil applied with BGF different levels (0, 2, 4 and 8 Mg ha -1 ) were investigated by closed-chamber method during rice cultivation period. CH₄ flux significantly decreased (p -1 of BGF addition in soil reduced CH₄ flux by 60.6% compared to control. Decreased soil redox potential (Eh) resulted in increasing CH₄ emission through a CO₂ reduction reaction. The concentrations of dissolved calcium (Ca) and sulfate ion (SO₄ 2- ) in soil pore water were significantly increased as the application rate of BGF increased and showed negatively correlations with CH₄ flux. Decreased CH₄ flux with BGF application implied that SO₄ 2- ion led to decreases in electron availability for methanogen and precipitation reaction of Ca ion with inorganic carbon including carbonate and bicarbonate as a source of CH₄ formation under anoxic condition. BGF application also increased rice grain yield by 16% at 8 Mg ha -1 of BGF addition. Therefore, our results suggest that BGF application can be a good soil management practice to reduce CH₄ emission from paddy soil and to increase rice yield.

National-scale paddy-upland rotation in Northern China promotes sustainable development of cultivated land

As China requires more cultivated land to feed its increasing population, the sustainable development of cultivated land in its intensive agricultural production system has become a major issue for government and society. We firstly reviewed the progress of paddy-upland rotation (PUR) and conservation tillage, found that PUR was improve significantly soil properties, including redox potential of soil, the mineralization of soil organic matter, and the abundance of beneficial microorganisms, suggested that conservation tillage was an effective measurement for remedying the deficiency under the PUR. Meanwhile, we also systemically reviewed the statues of water resource infrastructure and policy level. Consequently, with current agriculture technology and the increasing capacity of adjusted artificial water resources, our results highlight the development of national-scale PUR as an effective adaptation strategy to protect and improve soil fertility and ensure agricultural security under climate change. In other words, from national strategy scale, national-scale PUR was a good choice in the major grain-producing areas of northern China in the coming 50–100 years. Lastly, further research in the few aspects was needed to better provide theoretical and technical support for promoting effectively the PUR.