PHOSPHORUS RELEASE AND ASSIMILATORY CAPACITY OF TWO LOWER MISSISSIPPI VALLEY FRESHWATER WETLAND SOILS1

ABSTRACT: Phosphorus fluxes and water quality functions of a bottomland hardwood and freshwater marsh wetland soil were compared. The effect of soil physicochemical conditions, phosphorus loading rate, and diffusive exchange between soils and the overlying food water column on phosphorus release and retention were studied. The predominantly mineral swamp forest soil displayed greater phosphorus sorption potential than the organic freshwater marsh soil. Moreover, due to its low bulk density (0.11 g cm^?3), the freshwater marsh soil surface area required for phosphorus retention is very large compared to the bottomland hardwood wetland soil. For both wetlands, soil redox status affected P release and assimilatory capacity. The more reducing the soils, the smaller their phosphorus retention capacity (greater their release). Phosphorus removal from the overlying water column into the wetland soils followed a first-order kinetic model. Under similar hydrological conditions, phosphorus was found to diffuse 1.2 times faster to the bottom. land hardwood soil than in the freshwater marsh soil. Results indicate that while the bottomland hardwood wetland soil will serve as a sink for phosphorus entering such wetland, phosphorus will be released and exported from the freshwater marsh soil into adjacent ecosystems.     

Biochar and manure affect calcareous soil and corn silage nutrient concentrations and uptake

Carbon-rich biochar derived from the pyrolysis of biomass can sequester atmospheric CO, mitigate climate change, and potentially increase crop productivity. However, research is needed to confirm the suitability and sustainability of biochar application to different soils. To an irrigated calcareous soil, we applied stockpiled dairy manure (42 Mg ha dry wt) and hardwood-derived biochar (22.4 Mg ha), singly and in combination with manure, along with a control, yielding four treatments. Nitrogen fertilizer was applied when needed (based on preseason soil test N and crop requirements) in all plots and years, with N mineralized from added manure included in this determination. Available soil nutrients (NH-N; NO-N; Olsen P; and diethylenetriaminepentaacetic acid-extractable K, Mg, Na, Cu, Mn, Zn, and Fe), total C (TC), total N (TN), total organic C (TOC), and pH were evaluated annually, and silage corn nutrient concentration, yield, and uptake were measured over two growing seasons. Biochar treatment resulted in a 1.5-fold increase in available soil Mn and a 1.4-fold increase in TC and TOC, whereas manure produced a 1.2- to 1.7-fold increase in available nutrients (except Fe), compared with controls. In 2009 biochar increased corn silage B concentration but produced no yield increase; in 2010 biochar decreased corn silage TN (33%), S (7%) concentrations, and yield (36%) relative to controls. Manure produced a 1.3-fold increase in corn silage Cu, Mn, S, Mg, K, and TN concentrations and yield compared with the control in 2010. The combined biochar-manure effects were not synergistic except in the case of available soil Mn. In these calcareous soils, biochar did not alter pH or availability of P and cations, as is typically observed for acidic soils. If the second year results are representative, they suggest that biochar applications to calcareous soils may lead to reduced N availability, requiring additional soil N inputs to maintain yield targets.     

Environmental fate of triasulfuron in soils amended with municipal waste compost

The amendment of soil with compost may significantly influence the mobility and persistence of pesticides and thus affect their environmental fate. Factors like adsorption, kinetics, and rate of degradation of pesticides could be altered in amended soils. The aim of this study was to determine the effects of the addition of compost made from source-separated municipal waste and green waste, on the fate of triasulfuron [(2-(2-chloroethoxy)-N-[[4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide], a sulfonylurea herbicide used in postemergence treatment of cereals. Two native soils with low organic matter content were used. A series of analyses was performed to evaluate the adsorption and degradation of the herbicide in soil and in solution after the addition of compost and compost-extracted organic fractions, namely humic acids (HA), fulvic acids (FA), and hydrophobic dissolved organic matter (HoDOM). Results have shown that the adsorption of triasulfuron to soil increases in the presence of compost, and that the HA and HoDOM fractions are mainly responsible for this increase. Hydrophobic dissolved organic matter applied to the soils underwent sorption reactions with the soils, and in the sorbed state, served to increase the adsorption capacity of the soil for triasulfuron. The rate of hydrolysis of triasulfuron in solution was significantly higher at acidic pH and the presence of organic matter fractions extracted from compost also slightly increased the rate of hydrolysis. The rate of degradation in amended and nonamended soils is explained by a two-stage degradation kinetics. During the initial phase, although triasulfuron degradation was rapid with a half-life of approximately 30 d, the presence of compost and HoDOM was found to slightly reduce the rate of degradation with respect to that in nonamended soil.     

Effects of biochar addition on greenhouse gas emissions and microbial responses in a short-term laboratory experiment

Biochar application to soil has drawn much attention as a strategy to sequester atmospheric carbon in soil ecosystems. The applicability of this strategy as a climate change mitigation option is limited by our understanding of the mechanisms responsible for the observed changes in greenhouse gas emissions from soils, microbial responses, and soil fertility changes. We conducted an 8-wk laboratory incubation using soils from PASTURE (silt loam) and RICE PADDY (silt loam) sites with and without two types of biochar (biochar from swine manure [CHAR-M] and from barley stover [CHAR-B]). Responses to addition of the different biochars varied with the soil source. Addition of CHAR-B did not change CO and CH evolution from the PASTURE or the RICE PADDY soils, but there was a decrease in NO emissions from the PASTURE soil. The effects of CHAR-M addition on greenhouse gas emissions were different for the soils. The most substantial change was an increase in NO emissions from the RICE PADDY soil. This result was attributed to a combination of abundant denitrifiers in this soil and increased net nitrogen mineralization. Soil phosphatase and N-acetylglucosaminidase activity in the CHAR-B-treated soils was enhanced compared with the controls for both soils. Fungal biomass was higher in the CHAR-B-treated RICE PADDY soil. From our results, we suggest CHAR-B to be an appropriate amendment for the PASTURE and RICE PADDY soils because it provides increased nitrogen availability and microbial activity with no net increase in greenhouse gas emissions. Application of CHAR-M to RICE PADDY soils could result in excess nitrogen availability, which may increase NO emissions and possible NO leaching problems. Thus, this study confirms that the ability of environmentally sound biochar additions to sequester carbon in soils depends on the characteristics of the receiving soil as well as the nature of the biochar.     

Experimental investigation of groundwater contamination by surface sources: Determination of adsorption capacity,diffusion, and sorption potential of selected anions in different soils

The present study investigated the fate and transport of two significant anions through soil to explore their potential as groundwater contaminants. The retention properties of chloride and sulfate in soils having several significantly different characteristics (soil‐1 and soil‐2) were determined using adsorption test and adsorption‐diffusion column experiments. The maximum adsorption capacity of chloride was 3.7 and 1.16 mg/g, respectively, in soil‐1 and soil‐2, with organic matter (OM) content of 3.92% and 4.69%, respectively. The sulfate adsorption obtained was 24.09% and 13.83%, respectively, in the two soils. The anions exhibited monolayer adsorption in the soils with replacement of hydroxyl ions from soils as the major mechanism of adsorption. On the other hand, the adsorption capacities obtained from the adsorption‐diffusion column experiment were about 100 times lower compared to that of the column tests of both of the soils. The maximum adsorption capacity of chloride was 0.03 mg/g and 0.01 mg/g, respectively, in soil‐1 and soil‐2, whereas that of sulfate was 0.04 mg/g and 0.03 mg/g. The empirical relation for depth of penetration (d) from a known spillage onto the soil surface was determined as a function of sorption capacity (S) and initial anion concentration (C) as d = 0.0073e^(?57S)C and d = 0.0038e^(?35S)C for chloride and sulfate, respectively.     

Influence of sugarcane bagasse-derived biochar application on nitrate leaching in calcaric dark red soil

Application of biochar has been suggested to improve water- and fertilizer-retaining capacity of agricultural soil. The objective of this study was to evaluate the effects of bagasse charcoal (sugarcane [ L.] bagasse-derived biochar) on nitrate (NO) leaching from Shimajiri Maji soil, which has low water- and fertilizer-retaining capacity. The nitrate adsorption properties of bagasse charcoal formed at five pyrolysis temperatures (400-800° C) were investigated to select the most suitable bagasse charcoal for NO adsorption. Nitrate was able to adsorb onto the bagasse charcoal formed at pyrolysis temperatures of 700 to 800° C. Nitrate adsorption by bagasse charcoal (formed at 800° C) that passed through a 2-mm sieve was in a state of nonequilibrium even at 20 h after the addition of 20 mg N L KNO solution. Measurements suggested that the saturated and unsaturated hydraulic conductivity of bagasse charcoal (800° C)-amended soils are affected by changes in soil tortuosity and porosity and the presence of meso- and micropores in the bagasse charcoal, which did not contribute to soil water transfer. In NO leaching studies using bagasse charcoal (800° C)-amended soils with different charcoal contents (0-10% [w/w]), the maximum concentration of NO in effluents from bagasse charcoal-amended soil columns was approximately 5% less than that from a nonamended soil column because of NO adsorption by bagasse charcoal (800° C). We conclude that application of bagasse charcoal (800°C) to the soil will increase the residence time of NO in the root zone of crops and provide greater opportunity for crops to absorb NO.     

Sorption kinetics of chlortetracyline and tylosin on sandy loam and heavy clay soils

Antibiotics may appear in the environment when manure, sewage sludge, and other organic amendments are added to soils. There is concern that the presence of antibiotics in soils may lead to the development of antibiotic-resistant bacteria which may spread to the rest of the environment. This paper aims at evaluating the sorption kinetics of two antibiotics frequently used in pig production. The results indicate that sorption of chlortetracycline (CTC) and tylosin (TYL) in sandy loam and clay occurs very fast. More than 95% of the CTC adsorption is completed within 10 min on both soils and of TYL within 3 h. These results suggest that 24-h soil and antibiotic solution mixtures is enough for sorption studies. Also, there is less likelihood that these antibiotics will leach through soil and appear in the ground water since their sorption on soils is very high unless they are carried by soil particles through preferential flow. There was also no effect of soil sterilization on sorption kinetics of these antibiotics thus suggesting that there is minimal probability of the antibiotics degrading by microorganisms during 24- to 48-h adsorption studies.     

One step forward toward characterization: some important material properties to distinguish biochars

Terra Preta research gave evidence for the positive influence of charred organic material (biochar) on infertile tropical soils. Facing global challenges such as land degradation, fossil energy decline, water shortage, and climate change, the use of biochar as a soil amendment embedded into regional matter cycles seems to provide an all-round solution. However, little is known about biochar effects on individual ecosystem processes. Besides, the term is used for a variety of charred products. Therefore, the aim of this study was to investigate principal material properties of different chars to establish a minimum set of analytical properties and thresholds for biochar identification. For this purpose, chars from different production processes (traditional charcoal stack, rotary kiln, Pyreg reactor, wood gasifier, and hydrothermal carbonization) were analyzed for physical and chemical properties such as surface area, black carbon, polycyclic aromatic hydrocarbons, and elemental composition. Our results showed a significant influence of production processes on biochar properties. Based on our results, to identify biochar suitable for soil amendment and carbon sequestration, we recommend using variables with the following thresholds: O/C ratio <0.4, H/C ratio <0.6, black carbon >15% C, polyaromatic hydrocarbons lower than soil background values, and a surface area >100 m g.     

Adsorption and transport of arsenic(V) in experimental subsurface systems

The adsorption and transport of As(V) in a heterogeneous, iron oxide-containing soil was investigated in batch and column laboratory experiments. The As(V) adsorbed rapidly to the soil over the first 48 h, but continued to adsorb slowly over the next several weeks, clearly indicating the potential for rate-limited transport. The equilibrium As(V) adsorption isotherm was markedly nonlinear, further indicating the potential for nonideal transport. A model developed for the adsorption of As(V) to hydrous ferric oxide (HFO) was able to predict the pH-dependent adsorption of As(V) to the soil in batch experiments within 0.116 to 0.726 root mean square error (RMSE). Arsenic(V) was significantly retarded in column transport experiments. The column transport experiments were modeled using the one-dimensional advection-dispersion equation, considering both linear and nonlinear adsorption equilibrium. Although the nonlinear local equilibrium model (NLLE, RMSE = 0.273) predicted the data better than the linear local equilibrium model (LLE, RMSE = 0.317), As(V) breakthrough occurred more rapidly than predicted by either model due to adsorption nonequilibrium. However, due to the presence of an irreversible or slowly desorbing fraction, the peak aqueous As(V) concentration (0.624 mg L(-1)) and the total amount of As(V) recovered (44%) was lower than predicted based on the two equilibrium models (NLLE and LLE). For the conditions used in this study [1 mg L(-1) As(V), pH 4.5 and 9,0-0.25 mM PO4, 0.53-1.6 cm min(-1) pore water velocity], the effect on As(V) mobility and recovery increased in the order pH < pore water velocity < PO4.     

Laboratory degradation studies of bentazone, dichlorprop, MCPA, and propiconazole in Norwegian soils

Laboratory degradation studies were performed in Norwegian soils using two commercial formulations (Tilt and Triagran-P) containing either propiconazole alone or a combination of bentazone, dichlorprop, and MCPA. These soils included a fine sandy loam from Hole and a loam from Kroer, both of which are representative of Norwegian agricultural soils. The third soil was a highly decomposed organic material from the Froland forest. A fourth soil from the Skuterud watershed was used only for propiconazole degradation. After 84 d, less than 0.1% of the initial MCPA concentration remained in all three selected soils. For dichlorprop, the same results were found for the fine sandy loam and the organic-rich soil, but in the loam, 26% of the initial concentration remained. After 84 d, less than 0.1% of the initial concentration of bentazone remained in the organic-rich soil, but in the loam and the fine sandy loam 52 and 69% remained, respectively. Propiconazole was shown to be different from the other pesticides by its persistence. Amounts of initial concentration remaining varied from 40, 70, and 82% in the reference soils after 84 d for the organic-rich soil, fine sandy loam, and loam, respectively. The organic-rich soil showed the highest capacity to decompose all four pesticides. The results from the agricultural soils and the Skuterud watershed showed that the persistence of propiconazole was high. Pesticide degradation was approximated to first-order kinetics. Slow rates of degradation, where more than 50% of the pesticide remained in the soil after the 84-d duration of the experiment, did not fit well with first-order kinetics.     

Dissolved organic carbon in runoff and tile-drain water under corn and forage fertilized with hog manure

Dissolved organic carbon (DOC) export from soils can play a significant role in soil C cycling and in nutrient and pollutant transport. However, information about DOC losses from agricultural soils as influenced by management practices is scarce. We compared the effects of mineral fertilizer (MF) and liquid hog manure (LHM) applications on the concentration and molecular size of DOC released in runoff and tile-drain water under corn (Zea mays L.) and forage cropping systems. Runoff and tile-drain water samples were collected during a 2-mo period (October to December 1998) and DOC concentration was measured. Characterization of DOC was performed by tangential ultrafiltration with nominal cut-offs at 3 and 100 kDa. Mean concentration of DOC in runoff water (12.7 mg DOC L(-1)) was higher than in tile-drain water (6.5 mg DOC L(-1)). Incorporation of corn residues increased the DOC concentration by 6- to 17-fold in surface runoff, but this effect was short-lived. In runoff water, the relative size of the DOC molecules increased when corn residues and LHM were applied probably due to partial microbial breakdown of these organic materials and to a faster decomposition or preferential adsorption of the small molecules. The DOC concentration in tile-drain water was slightly higher under forage (7.5 mg DOC L(-1)) than under corn (5.4 mg DOC L(-1)) even though the application rates of LHM were higher in corn plots. We suggest that preferential flow facilitated the migration of DOC to tile drains in forage plots. In conclusion, incorporation of corn residues and LHM increased the concentration of DOC and the relative size of the molecules in surface runoff water, whereas DOC in tile-drain water was mostly influenced by the cropping system with relatively more DOC and larger molecules under forage than corn.     

TRANSPORT AND FATE OF ATRAZINE IN MIDWESTERN RIPARIAN BUFFER STRIPS1

ABSTRACT: The fate of pesticides entering the Riparian Buffer Strips (RBS) has not been well documented. This study compared the transport and fate of atrazine in soil of three‐, five‐, and nine‐year‐old switchgrass (Panicum virgatum L.) RBS to that in adjacent soils cropped to a corn‐soybean rotation or a grass‐alfalfa pasture. Undisturbed soil columns were collected from the RBS and cropped areas within the Bear Creek watershed, near Roland, Iowa. Atrazine and bromide breakthrough curves obtained using intact soil columns under saturated conditions were described by a two‐region, mobile‐immobile transport model. Preferential flow of bromide and atrazine was evident in five‐and nine‐year‐old RBS soil, but there was little difference in transport characteristics between these two RBS soils and the adjacent cropped soils. There was a trend towards an increase in dispersion coefficients between the five‐and nine‐year‐old RBS sites, which suggests an increased degree of preferential flow with increasing RBS age. Despite similar texture and organic C contents, atrazine sorption was significantly greater in RBS soil than the adjacent cropped soil. Cropped soil degraded atrazine faster than the RBS soil. The rapid degradation of atrazine in the corn‐soybean soil adjacent to the five‐year‐old RBS (atrazine half‐life of 19 days) appeared to be due to a larger population of atrazine‐degrading microorganisms. Atrazine‐degrading microorganisms in the corn‐soybean soil were 50,940 cells g^‐1 soil compared with 2,970 cells g^‐4 soil in 5‐year‐old RBS soil which resulted in 60 percent mineralization of [¹⁴C‐UL‐atrazine] in the corn‐soybean soil.     

Biochar pyrolyzed at two temperatures affects Escherichia coli transport through a sandy soil

The incorporation of biochar into soils has been proposed as a means to sequester carbon from the atmosphere. An added environmental benefit is that biochar has also been shown to increase soil retention of nutrients, heavy metals, and pesticides. The goal of this study was to evaluate whether biochar amendments affect the transport of Escherichia coli through a water-saturated soil. We looked at the transport of three E. coli isolates through 10-cm columns packed with a fine sandy soil amended with 2 or 10% (w/w) poultry litter biochar pyrolyzed at 350 or 700°C. For all three isolates, mixing the high-temperature biochar at a rate of 2% into the soil had no impact on transport behavior. When added at a rate of 10%, a reduction of five orders of magnitude in the amount of E. coli transported through the soil was observed for two of the isolates, and a 60% reduction was observed for the third isolate. Mixing the low-temperature biochar into the soil resulted in enhanced transport through the soil for two of the isolates, whereas no significant differences in transport behavior were observed between the low-temperature and high-temperature biochar amendments for one isolate. Our results show that the addition of biochar can affect the retention and transport behavior of E. coli and that biochar application rate, biochar pyrolysis temperature, and bacterial surface characteristics were important factors determining the transport of E. coli through our test soil.     

Estimation of effect of sugarcane bagasse biochar amendment in landfill soil cover on geotechnical properties and landfill gas emission

In a sanitary landfill, the final cover plays an important role in reducing the landfill gas emission to the atmosphere and in preventing the ingress of rainwater into the dumped waste. The present study investigated the suitability of sugarcane bagasse biochar as an amendment to the cover soil to improve the required landfill liner properties. The amended cover soil sugarcane bagasse (SSB) was tested for its stability and effectiveness, in terms of both geotechnical properties and methane mitigation efficiency. The effects of amending 15%, 20%, and 25% of sugarcane bagasse biochar (passing through 300 micron Indian Standard sieve) on the geotechnical properties of the SSB indicated that the SSB with 25% biochar showed the required values as per the standard with maximum dry density of 1.57 grams per cubic centimeter (g/cm³), liquid limit, plasticity index, and percentage of fines 48.5%, 16.3%, and 74.7%, respectively, and permeability of 0.9 × 10^?7. A column study that was conducted to determine the methane emission from the cover soil showed a 65.8% reduction in the methane emission compared to that of a column without SSB cover, with a cumulative methane emission of 410 milliliters (mL) at the end of 200 hours (h). On the other hand, the volume of methane emitted after 310 h from the column without cover and with the SSB cover was 1850 mL and 692 mL, respectively. The difference between these two values is found to be 22% of the total methane that the cover would have handled in its lifetime (5267 mL). Thus, there is an increase in the percentage of methane adsorption by soil cover from 15% to 22% when the soil was amended with 25% sugarcane bagasse biochar.     

Detailed characterization of solute transport in a heterogeneous field soil

There is a necessity for improved physical understanding of solute transport processes in heterogeneous soil systems. In situ nondestructive techniques like time domain reflectometry (TDR) and fiber optic miniprobes (FOMPs) permit the collection of unique measurements of solute transport processes in soils for the purposes of model development and validation. This study examined the application of TDR and FOMPs to measure solute transport at various points laterally and at two depths in a heterogeneous clay-loam soil. A miscible displacement experiment was performed at a constant irrigation flux to examine the applicability of these probes to field soils. In their first application to a field soil, the FOMPs were successfully calibrated and performed well in measuring solute breakthrough curves. Two flow regimes were identified in the soil profile, the first where lateral spreading of the solute occurred in the surface horizon, followed by convergence into preferential flow pathways in the second transport zone. The measured transport response was heterogeneous with at least two identifiable vertical flow phases. It was demonstrated using transfer function modeling and data from a corresponding laboratory study that the FOMPs were measuring the slower phase, while the TDR probes captured a composite of the fast and slow phases. The combination of these two techniques may be a means to separate solute transport phases in heterogeneous media and relate laboratory column results to field studies.     

Extent of pyrolysis impacts on fast pyrolysis biochar properties

A potential concern about the use of fast pyrolysis rather than slow pyrolysis biochars as soil amendments is that they may contain high levels of bioavailable C due to short particle residence times in the reactors, which could reduce the stability of biochar C and cause nutrient immobilization in soils. To investigate this concern, three corn ( L.) stover fast pyrolysis biochars prepared using different reactor conditions were chemically and physically characterized to determine their extent of pyrolysis. These biochars were also incubated in soil to assess their impact on soil CO emissions, nutrient availability, microorganism population growth, and water retention capacity. Elemental analysis and quantitative solid-state C nuclear magnetic resonance spectroscopy showed variation in O functional groups (associated primarily with carbohydrates) and aromatic C, which could be used to define extent of pyrolysis. A 24-wk incubation performed using a sandy soil amended with 0.5 wt% of corn stover biochar showed a small but significant decrease in soil CO emissions and a decrease in the bacteria:fungi ratios with extent of pyrolysis. Relative to the control soil, biochar-amended soils had small increases in CO emissions and extractable nutrients, but similar microorganism populations, extractable NO levels, and water retention capacities. Corn stover amendments, by contrast, significantly increased soil CO emissions and microbial populations, and reduced extractable NO. These results indicate that C in fast pyrolysis biochar is stable in soil environments and will not appreciably contribute to nutrient immobilization.     

The influence of biochar and black carbon on reduction and bioavailability of chromate in soils

The widespread use of chromium (Cr) has a deleterious impact on the environment. A number of pathways, both biotic and abiotic in character, determine the fate and speciation of Cr in soils. Chromium exists in two predominant species in the environment: trivalent [(Cr(III)] and hexavalent [Cr(VI)]. Of these two forms, Cr(III) is nontoxic and is strongly bound to soil particles, whereas Cr(VI) is more toxic and soluble and readily leaches into groundwater. The toxicity of Cr(VI) can be mitigated by reducing it to Cr(III) species. The objective of this study was to examine the effect of organic carbon sources on the reduction, microbial respiration, and phytoavailability of Cr(VI) in soils. Organic carbon sources, such as black carbon (BC) and biochar, were tested for their potential in reducing Cr(VI) in acidic and alkaline contaminated soils. An alkaline soil was selected to monitor the phytotoxicity of Cr(VI) in sunflower plant. Our results showed that using BC resulted in greater reduction of Cr(VI) in soils compared with biochar. This is attributed to the differences in dissolved organic carbon and functional groups that provide electrons for the reduction of Cr(VI). When increasing levels of Cr were added to soils, both microbial respiration and plant growth decreased. The application of BC was more effective than biochar in increasing the microbial population and in mitigating the phytotoxicity of Cr(VI). The net benefit of BC emerged as an increase in plant biomass and a decrease in Cr concentration in plant tissue. Consequently, it was concluded that BC is a potential reducing amendment in mitigating Cr(VI) toxicity in soil and plants.     

Biochar: a synthesis of its agronomic impact beyond carbon sequestration

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.     

Adsorption of methylene blue from aqueous solution by jackfruit (Artocarpus heteropyllus) leaf powder: A fixed-bed column study

Continuous fixed-bed studies were undertaken to evaluate the efficiency of jackfruit leaf powder (JLP) as an adsorbent for the removal of methylene blue (MB) from aqueous solution under the effect of various process parameters like bed depth (5–10 cm), flow rate (30–50 mL/min) and initial MB concentrations (100–300 mg/L). The pH at point of zero charge (pH_PZC) of the adsorbent was determined by the titration method and a value of 3.9 was obtained. A FTIR of the adsorbent was done before and after the adsorption to find the potential adsorption sites for interaction with methylene blue molecules. The results showed that the total adsorbed quantities and equilibrium uptake decreased with increasing flow rate and increased with increasing initial MB concentration. The longest breakthrough time and maximum MB adsorption were obtained at pH 10. The results showed that the column performed well at low flow rate. Also, breakthrough time and exhaustion time increased with increasing bed depth. The bed-depth service time (BDST) model and the Thomas model were applied to the adsorption of MB at different bed depths, flow rates, influent concentrations and pH to predict the breakthrough curves and to determine the characteristic parameters of the column that are useful for process design. The two model predictions were in very good agreement with the experimental results at all the process parameters studied indicating that they were very suitable for JLP column design.