Anaerobic Soil Conditions Research Articles

Systematic evaluation of methods for iron-impregnation of biochar and effects on arsenic in flooded soils.

There is a need for innovative strategies to decrease the mobility of metal(loids) including arsenic (As) and cadmium (Cd) in agricultural soils, including rice paddies, so as to minimize dietary exposure to these toxic elements. Iron (Fe)-modified biochars (FBCs) are used to immobilize As and Cd in soil-water systems, but there is a lack of clarity on optimal methods for preparing FBCs because there are only limited studies that directly compare BCs impregnated with Fe under different conditions. There is also a lack of information on the long-term performance of FBCs in flooded soil environments, where reductive dissolution of Fe (oxy)hydroxide phases loaded onto biochar surfaces may decrease the effectiveness of FBCs. This study uses material characterization methods including FTIR, SEM-EDX, BET, and adsorption isotherm experiments to investigate the effects of Fe-impregnation methods (pH, pyrolysis sequence, and sonication) on the morphology and mineralogy of Fe loaded onto the biochar surface, and to FBC adsorbent properties for arsenate (As(V)), arsenite (As(III)), and Cd. Acidic impregnation conditions favored the adsorption of As(III) onto amorphous Fe phases that were evenly distributed on the biochar surface, including within the biochar pore structure. The combination of sonication with acidic Fe-impregnation conditions led to the best adsorption capacities for As(V) and As(III) (4830 and 11,166 μg As g-1 biochar, respectively). Alkaline Fe-impregnation conditions led to the highest Cd adsorption capacity of 3054 μg Cd g-1 biochar, but had poor effectiveness as an As adsorbent. Amending soil with 5% (w/w) of an acid-impregnated and sonicated FBC was more effective than an alkaline-impregnated FBC or ferrihydrite in decreasing porewater As concentrations. The acid-impregnated FBC also had greater longevity, decreasing As by 54% and 56% in two flooded phases, probably due to the greater stability of Fe(III) within the biochar pore structure that may have a direct chemical bond to the biochar surface. This study demonstrates that FBCs can be designed with selectivity towards different As species or Cd and that they can maintain their effectiveness under anaerobic soil conditions. This is the first study to systematically test how impregnation conditions affect the stability of FBCs in soils under multiple drying-rewetting cycles.

Assessment of roadside grassland soil carbon characteristics

Carbon is a vital component of soil health and plays a crucial role in supporting plant growth and ecosystem functioning. By understanding the carbon content and characteristics of roadside grassland soil, we can evaluate its fertility and potential for supporting vegetation. Assessing roadside grassland soil carbon characteristics is important for understanding soil fertility, carbon sequestration potential, and the impact of human activities on soil health. The investigation includes elemental analysis of grassland soil and on that base calculation of ratios, soil organic carbon, soil carbon stocks, the carbon dioxide equivalent emissions from SCS soil carbon stocks loss. The samples have more percentage of element hydrogen which contribute to anaerobic conditions in grassland soil include waterlogging or poor drainage, high organic matter content, and compacted soil. The C/N (Carbon to Nitrogen) ratio is low and this is the reason of delayed decomposition and difficulties of nutrient cycling processes within the ecosystem. The soil organic carbon varies between 1 % and 2 %. Soil carbon stock between 304gC and 474 gC may be considered relatively low. The carbon dioxide equivalent emissions from SCS soil carbon stocks loss was between 2 and 3 %. This loss in carbon dioxide equivalent emissions from soil carbon stocks can be considered relatively low and potentially beneficial. Implementing practices that promote carbon sequestration, such as reducing soil disturbance, implementing cover cropping, and adopting sustainable land management practices, can help mitigate soil carbon loss and reduce emissions.

The Influence of Climatic Conditions and Agronomic Practices on Greenhouse Gas Emissions in a Conventional Vineyard (DOCa. Rioja, Spain)

Greenhouse gas (GHG) emissions are influenced by physical, chemical, biological, and anthropogenic factors. The objective of the study is to carry out a comprehensive analysis of the emissions of three important agricultural GHGs (CO2, N2O, and CH4) in both rows and alleys of a vineyard (1) and to understand their interactions with the agricultural operations carried out in the experimental plot, namely tillage, inter-row management, application of mineral and organic fertilizers, and irrigation and pruning, as well as the agroclimatic conditions of the plot (2). The study was conducted in a vineyard of Vitis vinifera L. cv. Tempranillo blanco in the DOCa. Rioja grape-growing region, during 2017, 2018, and 2019. Cumulative CO2 emissions were highest in 2018, reaching 934.7 ± 66.5 kg ha−1 day−1 in the alleys and 926.8 ± 76.5 kg ha−1 day−1 in the rows, in agreement with the wetter year and organic matter decomposition at the end of 2017. N2O emissions during the three-year study were mainly affected by mineral fertilizer application, with increases of 41.1 g ha−1 day−1 in the alleys and 49.3 g ha−1 day−1 in the rows during 2018, and 33.1 g ha−1 day−1 in the alleys and 39.6 g ha−1 day−1 in the rows in 2019. Regarding CH4, anaerobic soil conditions in 2018 (the year with the highest rainfall) led to the highest flux of CH4 emissions to the atmosphere, with 215.5 ± 51.0 g ha−1 day−1 in the corridors and 238.4 ± 54.9 g ha−1 day−1 in the rows. This study emphasizes the complex interplay of physical, chemical, biological, and human-related factors affecting GHG emissions in viticultural soils. Understanding these dynamics is essential for developing sustainable vineyard practices that minimize emissions and contribute to climate change mitigation.

Humus Forms of Moist and Wet Forest Stands. A Review

The organic layer of forest soils (forest floor) provides important ecosystem functions and serves as a habitat for soil organisms. This review provides an overview of research on humus forms of moist and wet forest stands based on a systematic literature review. Detailed information was collected from around 80 articles and books. It was examined whether the articles include the chemical, physical, or biological properties of humus forms. In addition, selected topics associated with and often used in relation to moist or wet humus forms, like information on morphological properties or information on specific classification systems, are considered. In general, it was found that many articles include the importance of moist or wet humus forms in their classification system. However, there was less or insufficient explanation on morphological properties. The humus forms on poorly drained or even waterlogged sites differ from humus forms on well-drained sites because the water factor affects the processes and thus the morphology very much. High soil moisture (=water saturation) means periodically anaerobic conditions in mineral soil and also very often in organic layers. Hence, soil organic carbon and soil organisms are affected. Especially, the recent literature often deals with climate change and soil organic carbon in moist and wet forest stands.

Optimal Straw Retention Strategies for Low-Carbon Rice Production: 5 Year Results of an In Situ Trial in Eastern China

Crop straw retention in the rice-based rotation cropland has been widely accepted as an effective method to improve soil quality in China. Rice–wheat rotation cropland is one the most prevalent rice-based rotation patterns, where it only exploits a small proportion of the total agricultural land yet feeds the majority of the Chinese population. Previous studies indicated that the incorporation of fore-rotating crop straw can effectively facilitate soil carbon sequestration in rice paddy fields. However, the application of crop straw may increase methane (CH4) emissions from rice paddies due to the anaerobic soil condition. To mitigate CH4 emissions from rice paddies while still preserving their soil carbon sequestration ability, a field experiment was conducted in the 2012–2016 rice growing seasons to determine the optimal low-carbon crop straw retention strategy. Five treatments with different wheat straw retention strategies were employed in this study, including non-fertilization and non-straw (Control), conventional fertilization without straw incorporation (CF), conventional fertilization with wheat straw incorporation (FS), slow-release fertilizer combined with wheat straw (SFS), and conventional fertilization with wheat-straw-derived biochar (FB). The results indicated that FS, SFS, and FB treatments significantly increased soil carbon sequestration in comparison with CF treatment. However, the increment of soil carbon sequestration was offset by raw wheat straw induced excess CH4 emissions under FS and SFS treatments. In contrast, the application of wheat-straw-derived biochar significantly promoted soil carbon sequestration, but showed no significant effect on CH4 emissions. Collectively, to the farmers, who aim to achieve agricultural carbon neutrality, the application of straw-derived biochar is worthy of consideration in rice cultivation processes.

Distribution of mangroves with different aerial root morphologies at accretion and erosion sites in Ca Mau Province, Vietnam

Aerial roots are a vital feature that allow mangroves to survive in anaerobic and unstable soil conditions. Mangrove species have different aerial root characteristics and show their own site-specific distribution. The distribution of three types of aerial roots with different morphological characteristics was investigated between accretion and erosion sites in Ca Mau, Vietnam. Stilt roots, pneumatophores and knee roots were the three main aerial root types in the study area. Stilt roots of Rhizophora apiculata BL. and pneumatophores of Avicennia species were the two most abundant root types at the study sites, dominating erosion and accretion sites, respectively. Stilt roots had a higher number of primary roots in seaward plots than in landward plots (p < 0.05), supporting the ability of R. apiculata to withstand erosion of the surface. Tidal erosion moved away sediment and exposed roots, which resulted in higher aboveground stilt root height in seaward plots than in landward plots at erosion sites (p < 0.05). The higher density and biomass of pneumatophores in seaward plots than those in landward plots at accretion sites (p < 0.05) confirmed the adaptation of Avicennia to newly accreted sites where tidal inundation and anaerobic conditions limited mangrove growth. The density of A. alba decreased with the distance from the sea at both erosion and accretion sites, implying that this species was a pioneer species adapted to newly accreted sites or disturbed sites among mangrove species. Bruguiera parviflora with knee roots was distributed in more stable conditions. Mangrove species with different root types displayed a zonal distribution with increasing distance from the shoreline. This distribution reflects mangrove species adaptabilities and species-specific roles in the context of coastal processes and site conditions, which should be considered in coastal mangrove restoration.

Rapid formation of iron monosulfide on Indicator of Reduction in Soil devices in S‐rich hydric soils

AbstractIndicator of Reduction in Soil (IRIS) devices are used to identify anaerobic conditions in soils for hydric soil and wetland identification purposes. IRIS devices quantify anaerobic conditions via the visualization of iron (Fe) reduction (e.g., orange Fe3+ paint reduces to soluble Fe2+, leaving behind the bare, white polyvinyl chloride device). Under stronger reducing conditions, sulfate (SO42−) reduction can occur, and sulfides (S2− and/or H2S) can react with the Fe3+ paint, resulting in the precipitation of black‐colored, reduced iron monosulfide (FeS). While these processes are well known, the rate of FeS formation remains relatively understudied and current IRIS methods may not capture these data accurately. This study investigated FeS formation on IRIS films to identify deployment times that capture the minimum and maximum precipitation of FeS. To determine the timing and magnitude of FeS‐precipitation on IRIS films, five replicate films were deployed in a wet, S‐rich soil, across 11 periods ranging from 2 min to 30 days. Results show that FeS precipitated on IRIS films in just 2 min, and the highest average amount of FeS (82%) precipitated in 1 day. After 1 day, the percentage of FeS decreased and a white color change became more apparent on IRIS films. Our results suggest that the recommended 30‐day deployment period is too long for accurately measuring FeS‐precipitation on IRIS devices deployed in wet, alkaline soils. These considerations should be incorporated into standard IRIS protocols used to quantify anaerobic conditions and other biogeochemical conditions (e.g., pore‐water sulfide levels) in S‐rich soils.

Catchment scale spatial distribution of soil enzyme activities in a mountainous German coniferous forest

Topography features within catchments influence soil properties, nutrient status, microbial dynamics and ultimately enzyme activities. Extracellular soil enzymes are essential for the decomposition of organic substrates and play a central role in global biogeochemical cycles. How topography and soil properties drive the spatial expression of enzyme activities at the catchment scale is still underexplored, especially in coniferous forest ecosystems. This study investigated the activity of four extracellular soil enzymes: β-glucosidase (β-glu), β-cellobiosidase (β-cello), acid phosphatase (pho) and leucine-aminopeptidase (l-leu) in Oh and Ah horizons of a (27 ha) mountainous coniferous forest catchment (Wüstebach, Eifel National Park, Germany). Spatial patterns and "hot spots" of activities of these four enzymes (involved in C-,N-, and P- cycling) were examined in connection to catchment units differing in slope, exposure and soil type (Cambisol vs. Gleysol), and multiple soil parameters (i.e., moisture content, pH, C, N, P, K, Fe, Mn content, C:N, C:P and N:P ratio). Catchment enzyme activities were overall, except for β-cello, significantly higher in the Oh than Ah horizon. Lower β-glu, and l-leu activities were found where more anaerobic soil conditions did occur, e.g., the river valleys (RV). Neither enhanced Oh horizon erosion on steeper Eastern (ES) and Northeastern (NES) slopes nor larger spatial soil nutrients heterogeneity on Northern (NS) and Western (WS) slopes, did significantly affect enzyme activity. Landscape topography did lead to a spatial variation of the activity of the four enzymes examined. The site-specific variation in C-cycling enzymes (β-glu and β-cello) was most marked at drier East, Northeast and Northern slopes, for P-cycling (pho) within the central wetter river valley but was for N-cycling (l-leu) enzyme activity more homogeneously distributed over the whole catchment. Overall, enzyme activities were strongly correlated to soil properties (especially soil moisture and organic carbon), but locations NS (Wüstebach source area) and RV (Wüstebach river flow path) showed less site-specific correlations. Further refinement of site-specific soil and external factors driving spatial distribution of enzyme activities at catchment scales and beyond will help to further tool up this research at larger spatial scales.

Macrotermes natalensis termite colonies in seasonally flooded savannas

In seasonally inundated landscapes of southern central Africa very large termite mounds of Macrotermes natalensis offer a refuge for flood-intolerant trees during the flood season. In the matrix landscape surrounding these islands the seasonally waterlogged and then anaerobic soil conditions and the browsing by megaherbivores during the dry season allow for grass and herbaceous vegetation only. During the rainy season each termitarium forms an isolated island which due to its relative dryness allows survival of the trees and the associated fauna. During the dry season the termites try to establish new colonies with new mounds. However, the successful formation of new termitaria islands seems to be a rare event. In this case study from Dundumwezi in the Kafue National Park, Zambia, we provide a description of the termitaria islands and their vegetation. Furthermore, we analyse spatial patterns of termite mound islands in the surroundings of Kafue National Park und Bangweulu Plains / Kasanka National Park based on remote sensing imagery. Our results confirm that competition among colonies of large termitaria in homogeneous habitats causes very regular spatial patterns.

Analysis of the vertical distribution of 137Cs and 239,240Pu in waterlogged and non-boggy soils by the sequential extraction method

Mobile capabilities of 137Cs, 239,240Pu and some stable element physicochemical forms were studied in soil layers at a depth of 6–8 cm (maximum concentrations of radionuclides) of non-boggy and waterlogged soil cores sampled on the shores of Lake Bedugnis (Lithuania). Soil samples were acidic with small amount of clay (muscovite). The radionuclide activity concentrations were about 2.5 times higher in non-boggy soil. It was explained by different conditions of deposition of radioactive fallout at these sampling sites and density of the soil samples. The value of the exchangeable fraction of radionuclides is shown to be an indicator of their migration capabilities in the soil. Under anaerobic conditions in waterlogged soil (stagnant pore water conditions) and due to the presence of clay admixture, ∼90% of 137Cs was concentrated in the residual fraction and its mobility was low. 239,240Pu was concentrated mainly in organic matter with rather large exchangeable fractions (∼9.6–∼13.9%). Under oxidizing conditions in non-boggy soil (dynamic pore water conditions in the case of rain), 239,240Pu was mostly concentrated in the oxide fraction. Its exchangeable fractions were less than those in waterlogged soil and, respectively, its mobility was lower. In non-boggy soils, exchangeable fractions of 137Cs were large and varied in the range of 10.1–12.2%, which indicated its high mobility. In the case, 137Cs adsorption by clay materials was reduced and its residual fraction did not exceed 71.3%. The obtained data show that in the area of Lake Bedugnis, the migration capabilities of 137Cs and 239,240Pu change in antiphase.

Scenario on Environmental Management to Reduce Green House Gas Emission Due To Low Land Rice Cultivation under Paddy Soils

As an important staple food crop rice production needs to be increased by 40% by the end of the 2030s to meet the increasing demand for food due to the expanding population. In this regard countries like Ethiopia having reasonable potential of rice production in various areas, mainly in rainfed lowland, upland and irrigated ecosystems are the major targets. But such Agricultural activities contribute to approximately 18.4% of to the present concentrations of GHGs emission followed by energy sector that are considered as one of the major sources of emissions however, this warming potential is a cumulative effect of 100 years horizon. CH 4 gas is produced under flooded or anaerobic soil conditions by the process of methanogenesis while N 2 O gas is produced through nitrification and denitrification processes. Consequently predicting the dynamic changes in emission of GHGs and rice yield in paddy fields and keeping the possible solution should be considered. From the scenarios of rice and green house gas emissions water managements on paddy soils as well as organic and inorganic fertilizations under plenty mass production of rice on paddy soils are top most considerable’s. Therefore conducting researches to fills the gap by determining the effect of nutrient and water management on rice yield and greenhouse gas emission should be developed and in lined with the mass production for the future. Keywords : Paddy Soils; Fertilization; Water Management; Green house gases DOI: 10.7176/JEES/12-4-01 Publication date: April 30 th 2022

Effects of Drainage Water Management in a Corn–Soy Rotation on Soil N2O and CH4 Fluxes

Drainage water management (DWM), also known as controlled drainage, is a best management practice (BMP) deployed on drainage ditches with demonstrated success at reducing dissolved nitrogen export from agricultural fields. By slowing discharge from agricultural ditches, subsequent anaerobic soil conditions provide an environment for nitrate to be reduced via denitrification. Despite this success, incomplete denitrification might increase nitrous oxide (N2O) emissions and more reducing conditions might increase methanogenesis, resulting in increased methane (CH4) emissions. These two gases, N2O and CH4, are potent greenhouse gases (GHG) and N2O also depletes stratospheric ozone. This potential pollution swapping of nitrate reduction for GHG production could negatively impact the desirability of this BMP. We conducted three years of static chamber measurements of GHG emissions from the soil surface in farm plots with and without DWM in a corn–soybean rotation on the Delmarva Peninsula. We found that DWM raised the water table at the drainage ditch edge, but had no statistically significant effect on water-filled pore space in the field soil surface. Nor did we find a significant effect of DWM on GHG emissions. These findings are encouraging and suggest that, at least for this farm site, DWM can be used to remove nitrate without a significant tradeoff of increased GHG emissions.

Decomposition of rice straw residues and the emission of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; under paddy rice and crop rotation in the Vietnamese Mekong Delta region - A microcosm study

This study investigated the influence of soil undergoing different crop rotations on the CH&lt;sub&gt;4&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt; emissions, and decomposition of rice straw. The studied soil undergoing crop rotation systems were rice-rice-rice (SR) and baby corn-rice-mungbean (SB). Two main microcosm set-ups: anaerobic (SR-AN, SB-AN) and aerobic (SR-AE, SB-AE) conditions. Litter bags containing rice stems were inserted into the soil and recollected at different time points for chemical analysing and the gas sampling was collected to measure the CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; emissions. The results indicated that the total carbon (TC) decreased around 30%, and the TC removal in anaerobic was significantly higher than in aerobic conditions. The residue cellulose content varied in a range from 68.2% to 78.6%, while the hemicellulose content varied from 57.4% to 69.3% at day 50 after incorporation. There were no significant differences in the total nitrogen removal, cellulose, hemicellulose, and lignin contents among the microcosm set-ups. CO&lt;sub&gt;2&lt;/sub&gt; emission increased in all the microcosm set-ups with the treatments without rice straw (CTSR, CTSB) in both aerobic and anaerobic conditions. CH&lt;sub&gt;4&lt;/sub&gt; release in the SR-AN treatments did not differ significantly compared with the SB-AN treatments. This study confirmed that the decomposition of rice straw residues is faster in the anaerobic paddy soil condition compared to the aerobic crop rotation condition.

Subsurface Nitrate Processing Beneath Drainageways: Are They Landscape Opportunities for Subsurface Drainage Remediation?

HighlightsDrainageways contain fine-textured and nutrient rich alluvial soils conducive for denitrification.NO3-N concentrations in drainageway groundwater were 70% lower than observed in cropped fields.A new grass waterway design connects subsurface water from upland cropped fields to the drainageway deposits for NO3-N remediation.Abstract. Efforts to reduce nutrient export from agricultural crop production in the U.S. Midwest are leading to development of new conservation practices. In this study our objectives were to: (1) characterize subsurface soils and hydrogeology found in two main drainageway areas in eastern Iowa, (2) compare groundwater quality to upland agricultural fields, and (3) utilize a groundwater flow model to assess the capacity of drainageways to provide additional NO3-N processing in agricultural watersheds. Using data obtained from a network of 12 shallow wells installed across six different waterways, we found that the waterways contained fine-textured and nutrient rich alluvial soils derived from erosion and deposition of upland loess and till. Concentrations of NO3-N in waterway groundwater (3.1 mg/l) were 70% lower compared to groundwater beneath nearby cropped fields (10.5 mg/l). A shallow water table in the organic-rich drainageway soils provides the requisite organic carbon, anaerobic soil conditions, and nitrogen supply for denitrification to occur. Numerical modeling suggested that groundwater from the surrounding catchment discharges approximately 53 m3/day into the waterways and reduces NO3-N mass by 144.3 kg/yr, or 7.8 kg/ha. Results suggest that drainageways could be better exploited for additional NO3-N reductions from subsurface drainage if the flow could be diverted into these areas. Keywords: Denitrification, Grass waterway, Nitrate-nitrogen, Saturated buffer.

РЕКРЕАЦИОННЫЕ ИЗМЕНЕНИЯ АЛЛЕЛОПАТИЧЕСКОЙ АКТИВНОСТИ КОРНЕВЫХ СИСТЕМ ДРЕВОСТОЯ В ЛЕСНЫХ ЭКОСИСТЕМАХ

The study of the influence of chronic recreational impact in forest ecosystems on the allelopathic activity of the root systems of arboreal species was carried out. It was determined that with an increase in the recreational impact, the transformation of the allelopathic activity of roots increases, averaging from 27.3 %, at stage II of recreational digression, to 83.4 % at stage V. Large values of activity at stage II are recorded in plantations with a smaller number of species in the stand. An increase in the load leading to stages III-V is accompanied by an increase in root exudates and a decrease in the biomass of small roots in communities with a large number of woody species (3-4 species). Active root ends are more sensitive to the number of species in the stand and to the recreational density of the soil throughout the entire range of recreational digression, reacting to a greater extent to the recreational load (soil compaction) at the stage of its manifestation (stage II, 35.7 %), the stage of critical recovery (stage III, 2.9 %) and at the highest stage (stage V, 90.4 %) of the forest community. A significant reaction at the highest loads, which fits into the regularities of anaerobic soil conditions, accompanied by self-poisoning of plant organisms as a result of the transformation of root exudates into highly reduced compounds, suggests that in the zone of highly compacted paths, root systems die not only due to a lack of oxygen for root respiration but also from poisoning with toxic compounds formed during the transformation of root secretions by anaerobic heterotrophs.

A perennial living mulch substantially increases infiltration in row crop systems

Poor infiltration in annual row crop systems can cause a range of problems, including sediment and nutrient loss in runoff, diminished trafficability, anaerobic soil conditions, and reduced precipitation use efficiency. Soils covered by perennial vegetation generally sustain much higher infiltration rates, and consequently are less prone to these problems. Kura clover (<i>Trifolium ambiguum</i> Bieb.) living mulch (KCLM) is a management system that seeks these environmental benefits of perenniality, while allowing continued production of annual row crops like maize (<i>Zea mays</i> L.) and soybean (<i>Glycine max</i> [L.] Merr.). This is done by planting them into tilled or killed strips within a perennial stand of kura clover. Our objective was to compare the hydrologic performance of long-term KCLM systems (in place for at least five years) against adjacent fields or plots in conventional row crop production on the same soil types. Measured variables included field-saturated hydraulic conductivity (K_fs), moisture release curves, and bulk density. K_fs was measured with a constant head single ring infiltrometer, and moisture release curves were determined with the evaporation method. Bulk density was measured on 5 cm diameter cores extracted from the surface horizon of each treatment. None of the long-term sites contained appreciable sloped land, so supporting runoff measurements were made on a third field in Minnesota where the KCLM had only been in place for two years, using lined plots with flumes and tipping buckets. Results revealed substantial and significant differences in K_fs at the long-term sites. At one site the mean value was 11 times greater in the living mulch than in the conventional fields, while at the other site it was 19 times greater. The runoff plots showed a 93% reduction in sediment loss for the KCLM relative to conventional production over the course of a year that included 10 runoff-inducing storms. These results suggest that KCLM may confer similar hydrologic benefits to prairie strips if strategically placed in fields or watersheds.

Alteration of Fractionation and Bioavailability of Arsenic (As) in Paddy Soil under Transition from Aerobic to Anaerobic Conditions

The impact of the change from aerobic to anaerobic immersed soil conditions on arsenic (As) fractionation (Tessier’s method) and its bioavailability (ethylene diamine tetraacetic acid extractable) were assessed. As-contaminated paddy soils were tested by laboratory simulation experiments. The samples were aerobic, with 35-49 mg/kg of As at low bioavailability (&lt;2%). Most As was distributed in the stable fraction (77%), followed by As bound to ferric and manganese oxide (17%) and organic compounds (5%), while the mobile fraction (exchangeable and mildly acid-soluble) was limited (1%). After one month under anaerobic simulation, redox potential reduced to less than zero (-32 to -124 mV). The stable fraction of As decreased (-17%), while the mobile fraction increased (+16%) and As bioavailability also increased (+26% total As). Increase in the As mobile fraction was associated with freshly precipitated compounds. The As content in the soil altered from a stable fraction to an available fraction when confined in an anaerobic environment for a long period. Results indicated that agricultural methods which promoted anaerobic conditions in As-contaminated soil should be avoided.

Enhancing soil ecosystem services through sustainable integrated nutrient management in double rice-cropping system of North-East India

The wetland cultivation of rice is subjected to anaerobic and aerobic soil conditions causing substantial changes in the soil system. However, how long-term supplementation of organics with reduced chemical fertilizers affects microbial composition, their activities, and enzymatic activities in acid soil has not been sufficiently investigated. This research is focused on a rice-rice system after an ongoing field experiment set-up in 1977–78 at Assam Agricultural University, Jorhat, India, where 7 alternative nutrient management have been investigated to: (1) assess the effects on soil organic carbon (SOC), microbial biomass carbon, and enzymatic activity in acid soil; (2) identify and discuss the most suitable treatment combinations of organic and chemical fertilizers to enhance soil ecosystem services (SES). Accordingly, we analysed the soil microbiological properties as affected by the 32 years of continuous integrated nutrient management (INM) practices and also evaluated the INM treatments in terms of SES. Results revealed that the soil microbial biomass carbon significantly varied across the treatments from 129.4 to 412.1 µg g−1 which comprises 2.4 to 4.4% of the SOC. The highest bacterial count (8.95 log cfu g−1 soil) was recorded in RDF + Azolla treatment, whereas fungal count was the maximum (7.47 log cfu g−1 soil) in RDF + FYM treatment. All the enzymatic activities responded significantly to the INM practices, but the trend of response was different for different enzymes. The highest dehydrogenase (223.6 µg TTF g−1 soil 24 h−1) and urease (4.1 μg NH4-N g−1 soil 2 h−1) activities were recorded in RDF + Azolla, while phosphomonoeaterase (337.4 μg p-nitrophenol g−1 soil h−1) and fluorescein diacetate hydrolysis (10.0 μg fluorescein g−1 soil h−1) activities were found to be the maximum in RDF + FYM. The microbial and enzymatic activities decreased significantly in the control after 32 cycles of rice-rice cropping. In this study, a significant positive statistical correlation of all the microbiological properties with soil pH, soil organic carbon and grain yield of crops were recorded. Finally, the different soil properties under the different nutrient treatments have been discussed in terms of SES provision, highlighting that the most sustainable treatments have resulted in RDF + FYM, RDF + RS and RDF + Azolla.

Volatile fatty acid concentration, soil pH and soil texture during anaerobic soil conditions affect viability of Athelia (Sclerotium) rolfsii sclerotia

Volatile fatty acid concentration, soil pH and soil texture during anaerobic soil conditions affect viability of Athelia (Sclerotium) rolfsii sclerotia

Kinetics of antimony biogeochemical processes under pre-definite anaerobic and aerobic conditions in a paddy soil

While the transformation of antimony (Sb) in paddy soil has been previously investigated, the biogeochemical processes of highly chemical active Sb in the soil remain poorly understood. In addition, there is a lack of quantitative understanding of Sb transformation in soil. Therefore, in this study, the kinetics of exogenous Sb in paddy soils were investigated under anaerobic and aerobic incubation conditions. The dissolved Sb(V) and the Sb(V) extracted by diffusive gradient technique decreased under anaerobic conditions and then increased under aerobic conditions. The redox reaction of Sb occurred, and Sb bioavailability significantly decreased after 55 days of incubation. The kinetics of Fe and the scanning transmission electron microscopy analysis revealed that the Fe oxides were reduced and became dispersed under anaerobic conditions, whereas they were oxidized and re-aggregated during the aerobic stage. In addition, the redox processes of sulfur and nitrogen were detected under both anaerobic and aerobic conditions. Based on these observations, a simplified kinetic model was established to distinguish the relative contributions of the transformation processes. The bioavailability of Sb was controlled by immobilization as a result of S reduction and by mobilization as a result of Fe reductive dissolution and S oxidation, rather than the pH. These processes coupled with the redox reaction of Sb jointly resulted in the complex behavior of Sb transformation under anaerobic and aerobic conditions. The model-based method and findings of this study provide a comprehensive understanding of the Sb transformation in a complex soil biogeochemical system under changing redox conditions.