Agricultural Soil Amendment Research Articles

A study of olive mill wastewaters obtained from different treatment processes effects on chemical and microbial properties of a Typic Xerofluvent soil and wheat yield

This study was carried out to investigate the potential for the usability of treated olive mill wastewater (OMW) as an organic amendment in agricultural soils under Mediterranean climate conditions. OMW was treated by two different treatment processes as economical (E-OMW) and advanced (A-OMW). The treated OMWs and raw OMW (R-OMW) were applied to a loamy soil at a rate of 100 m3 ha-1 year-1 for 2 years. Soils were sampled 15 days and about 5 months (at harvest) after OMW application for chemical and microbial analyses in each year. The total concentrations of N, P, Cu, Zn, and phenol of R-OMW decreased after both treatment processes while salinity (EC) and the total amounts of K, Na, and Ca increased. The applications of OMW caused changes in soil chemical (pH, EC, Pext, Kext) and microbial (microbial biomass-C (MB-C), microbial biomass-N (MB-N), basal soil respiration (BSR), N-mineralization (N-min)) characteristics (P < 0.05). In the second year of the experiment, initial samplings showed that the values of soil pH and EC increased significantly under all OMW applications compared to the control. High Pext concentrations were determined in soils amended with R-OMW, while there were high Kext concentrations in soils amended with the treated OMWs. The increases determined in MB-C and MB-N at all sampling times resulted in high MB-C/TOC and MB-N/TN ratios in soils amended with the treated OMWs. The wheat grain yield over the 2-year period showed that the application of the treated OMWs had a positive effect. It was determined that no negative effects occurred for either soil properties or wheat growth with the treated OMW applied at rates of up to 100 m3 ha-1. The addition of treated OMW after removal of its phenolic components may be considered as a good option for evaluating this waste in countries where OMW causes serious environmental pollution.

Impact of Low-Dose Municipal Sewage Sludge Compost Treatments on the Nutrient and the Heavy Metal Contents in a Chernozem Topsoil Near Újkígyós, Hungary: A 5-Year Comparison

Abstract Agriculture is one of the major fields, where sewage sludge can be used. Its high nutrient content can contribute to the improvement of important soil properties, such as nutrient content, water balance and soil structure. However, sewage sludge may contain hazardous components, such as pathogens and pollutants. Therefore, it is important to monitor the effects of its field application. In this paper, we assessed the impacts of two low-dose (2.5 m3/ha) municipal sewage sludge compost applications (in 2013 and in 2017) in a 5.6 ha arable land in southeast Hungary (near Újkígyós), located in the Hungarian Great Plain. The nutrient and the heavy metal contents in the upper soil layer (0-30 cm) of the studied Chernozem soils were compared between two sampling campaigns in 2013 (before the compost applications) and in 2018 (after the compost applications). Basic soil properties (pH, salinity, humus content, carbonate content, Arany yarn number) complemented with nutrient content (K2O, P2O5, NO2+ NO3) and heavy metal content (Cd, Co, Cr, Cu, Ni, Pb and Zn) analyses were performed. The results show that no significant change can be noticed in the baseline parameters over the 5-year period. The slight increase in the P2O5, NO2+ NO3 content is closely related to the beneficial effects of the sewage sludge deposition. The soil-bound heavy metal load did not increase significantly as a result of the compost treatments, only nickel showed a slight increase in the topsoil. In all cases the heavy metal concentrations did not reach the contamination thresholds set by Hungarian standards. The results provided positive evidences proving that low dose municipal sewage sludge compost disposal on agricultural land is safe, and can be considered as a sustainable soil amendment for agriculture in compliance with legal requirements.

Effect of Biochar on Soil Properties, Soil Loss, and Cocoyam Yield on a Tropical Sandy Loam Alfisol.

Among agricultural soil amendment that can enhance crop productivity and soil sustainability is biochar. Hence, two-year field experiments were conducted on a sandy loam Alfisol at Owo, southwest Nigeria, to evaluate the effects of biochar produced from hardwood on soil physical and chemical characteristics, erosion potential, and cocoyam (Xanthosoma sagittifolium (L.) Schott) yield. The study was a 2 × 4 factorial experiment with two years (2017 and 2018) and four biochar levels (0 (control), 10, 20, and 30 t ha−1). The treatments were laid out in a randomized complete block design with three replications. Results indicated that biochar application significantly in both years improved yield of cocoyam and soil physical (bulk density, porosity, moisture content, mean weight diameter (MWD) of soil aggregates, dispersion ratio, and infiltration rate) and chemical (soil organic matter, pH, N, P, K, Ca, Mg, and CEC) properties and erosion resistance. Soil characteristics and cocoyam yield improved with level of biochar from 0–30 t ha−1. When 2018 is compared with 2017 in term of soil loss, in the amended plots, 2018 reduced soil loss by 7.4, 20, and 73.5%, respectively, for 10, 20, and 30 t ha−1biochar, whereas there was an increase of 2.7% soil loss in the control plot in 2018 compared with 2017. Therefore, application rate of 30 t ha−1 biochar is considered as suitable for severely degraded soil because this application rate efficiently improves cocoyam yield and soil properties and reduces soil loss.

Application of FGD Waste for Degraded Soil Amendment for Sustainable Agriculture

The product from coal-fired power plants is flue gas desulfurization (FGD) waste. FGD has been used in many industries such as wallboard and cement industries. It can be applied in agriculture to make soil higher quality. The application of this waste in agriculture is scarce. The benefit of FGD waste can change the acidic condition in soil and increase the substance for plant growing to enhance soil quality. The degradation of soil is one of the main impacts for agricultural industries. Degraded soil is the soil with a decrease in quality because of excessive land use, overuse of chemical fertilizers, deforestation and clearing the land. In Thailand, degraded soil is a crucial problem especially in the northern areas. The aim of this work is to use the FGD waste from coal-fired power plants to enhance the soil quality in Nan, Thailand and to evaluate the effects of FGD waste mixture ranging from 5-40 % by weight on soil texture, bulk density, pH and electrical conductivity (EC). Based on the results, the higher amount of FGD waste in the mixture, the better quality of soil can be obtained, specifically soil texture and pH. The soil texture can be adjusted from clay to silt loam or loam. The pH increases from 5.664 up to 6.861. The soil bulk density reduces for all ratios of mixing with FGD waste which is conducive to plant growth. This study can be used for soil improvement and enhance the agricultural yields. The potential mixing ratios of 30 % to 40 % of FGD waste are expected to investigate the effects on plant growing and soil improvement in the real field for further study.

Response of chemical and microbial properties to short-term biochar amendment in different agricultural soils

The objective of this study was to assess the effect of biochar soil amendment (BSA) on chemical and microbial properties in different agricultural soils in Vojvodina Prov?ince. Short-term pot experiment consisted of five biochar application doses (0, 0.5, 1, 2, and 3%) and five contrasting soil types (Mollic Gleysol, Eutric Cambisol, Calcaric Fluvisol, Gleyic Chernozem, and Haplic Chernozem), planted with sunflower (Helianthus annuus L.) and winter wheat (Triticum aestivum L.). The examined chemical and microbial properties were significantly influenced by soil type and interaction of experimental factors. Significant influence of biochar on the contents of calcium carbonate (CaCO3), total nitrogen (N), total carbon (C), soil organic carbon (SOC), humus and potassium (K) of the tested soils was observed. Biochar also significantly affected the number of azotobacters (AZB), fungi (FNG), actino?mycetes (ACT) and copiotrophic bacteria (CB). The effect of BSA varied depending on the applied dose, with higher values of the examined chemical and microbial parameters at higher doses of application. Further studies on using biochar in soils with low fertility will be neces?sary to establish its efficiency as an enhancer for agricultural production in Serbia.

Liming Positively Modulates Microbial Community Composition and Function of Sugarcane Fields

Liming combined with an optimum quantity of inorganic fertilizer, as a soil amendment in intensive agriculture, is a viable agricultural practice in terms of improving soil nutrient status and productivity, as well as mitigating soil degradation. The chief benefits of this strategy are fundamentally dependent on soil microbial function. However, we have limited knowledge about lime’s effects on soil microbiomes and their functions, nor on its comprehensive influence on soil nutrient status and the productivity of sugarcane plantations. This study compares the impacts of lime application (1-year lime (L1), 2-year lime (L2), and no lime (CK) on microbial communities, their functions, soil nutrient status, and crop yield in a sugarcane cropping system. We employed Illumina sequencing and functional analysis (PICRUSt and FUNGuild) to decipher microbial communities and functions. In comparison with CK, lime application (L1 and L2) mitigated soil acidity, increased the level of base cations (Ca2+ and Mg2+), and improved soil nutrient status (especially through N and P) as well as soil microbial functions associated with nutrient cycling and that are beneficial to plants, thereby improving plant agronomic parameters and yield. Liming (L1 and L2) increased species richness and stimulated an abundance of Acidobacteria and Chloroflexi compared to CK. In comparison with CK, the two functional categories related to metabolism (amino acid and carbohydrate) increased in the L1 field, whereas cofactors and vitamin metabolites increased in the L2 field. Turning to fungi, compared to CK, liming enriched symbiotrophs (endophytes, ectomycorrhizae, and arbuscular mycorrhizae) and led to a reduction of saprotrophs (Zygomycota and wood saprotrophs) and pathotrophs. The observed benefits of liming were, in turn, ultimately reflected in improved sugarcane agronomic performance, such as increased stalk height and weight in the sugarcane planting system. However, the increase in the above-mentioned parameters was more prominent in the L2 field compared to the L1 field, suggesting consecutive liming could be a practical approach in terms of sustainable production of sugarcane.

Kenaf stems: Thermal characterization and conversion for biofuel and biochar production

Kenaf stems are characterized in this present investigation in order to assess their suitability in energy recovery through a pyrolysis process and to identify sustainable applications of the generated biochar. In particular, the raw biomass properties are analyzed using numerous analytical techniques such as thermogravimetric analyses (TGA/DTG), X-Ray Fluorescence (XRF) and Scanning Electronic Microscopy (SEM). First, the thermogravimetric analyses monitor the pyrolysis parameters, control the proportion of its outputs and allow to extract the kinetic parameters. The latter is determined using Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) models.In a second step, Kenaf derived chars are produced at different pyrolysis temperatures and their physicochemical, morphological, textural and structural properties are determined using different techniques such as CO2 adsorption, Raman Spectroscopy, and DRIFT Spectroscopy.The main results confirm the Kenaf potential for energy applications as its thermal properties are more interesting compared to other usual crops. The Kenaf stem derived char is also very promising for pollutants removal or gas storage as its surface area as well as its microporous structure are interestingly developed when increasing the pyrolysis temperature. Kenaf char could be also chemically or physically activated in order to be used for pollutants removal from gaseous and aqueous effluents.Finally, the XRF analysis indicated that contents in K and P elements are high. Ca and Mg are also major mineral species in the char. These contents indicate that Kenaf derived char could be also suitable for agricultural soil amendments.

Remediation of heavy metals and enhancement of fertilizing potential of a sewage sludge by the synergistic interaction of woodlice and earthworms

Woodlice and the earthworm alone or in combination were used to improve physical properties, nutrient release, and heavy metals stabilization during composting of sewage sludge. Chemical properties of raw sludge (IS) were compared to those of composted sludge (CS), sludge + earthworms (VS), sludge + woodlice (WS), and sludge + earthworms + woodlice (VWS) after 50 and 100 days of composting. Physical properties and heavy metals accumulation by the studied fauna was determined after 100 days of composting. Highest proportions of fine particles, porosity and water holding capacity were in the VWS treatment, electrical conductivity, ash content, inorganic N and the total concentrations of P, K, Ca and Mg increased, whereas the pH value, the organic C, C:N ratio and humic acids content decreased in following order: VWS > VC > WS > CS > IS. Total concentrations of Pb, Cd and Ni in composted sludge were lower whereas concentrations of Zn, Cu and Mn were higher than in raw sludge, and woodlice showed higher bioconcentration factor (BCFs) than earthworm for all heavy metals in all treatments. We concluded that woodlice and earthworms synergistically improved the physicochemical properties of the compost and enhanced its potential use as amendment in agricultural soils.

Assessing the quality of sewage sludge as an agricultural soil amendment in Mediterranean habitats

PurposeMunicipal sewage sludge generated from three operational wastewater treatment plants, located in the Bekaa valley of Lebanon, was assessed for its potential use as agricultural soil amendment.MethodsSludge samples were taken from three treatment plants located in the villages of Iaat, Ablah and Joub Jannine during the summer season of 2018, from June to September, on a monthly basis. The evaluation was based on characterizing the physicochemical parameters such as the metal content, the pathogenic microorganisms (Salmonella, E.Coli, Staphylococcus aureus, Helminth eggs, Ascaris, Acinetobacter) and the phytotoxicity–stability indicators of the sludge samples.ResultsThe obtained results were compared to the Lebanese guidelines for sludge reuse in agriculture. For the physicochemical analysis, all the samples showed a possibility to be used in agriculture due to the high content of minerals and organic matter. Considering the metal content of sludge, Iaat and Ablah sludge were classified as Class A according to the Lebanese guidelines; however, sludge from Joub Janine was classified as B due to its high content of zinc that exceeded the limit of 700 ppm. Helminth eggs and Salmonella were absent in the sludge samples. Pathogenic organisms, mainly E. coli, were detected in Iaat dry sludge, Staphylococcus aureus was present in Joub Jannine sludge and Acinetobacter in Ablah station (> 100 CFU/100 g).ConclusionIt is recommended to submit the sludge which did not meet the required criteria, for further treatments, particularly the composting process to reduce the metal content and pathogenic microorganisms for a safer reuse in agriculture.

Characterization of Physically Fractionated Wollastonite-Amended Agricultural Soils

Wollastonite is a natural silicate mineral that can be used as an agricultural soil amendment. Once in the soil, this mineral undergoes weathering and carbonation reactions, and, under certain soil and field crop conditions, our previous work has shown that this practice leads to accumulation of inorganic carbon (calcium carbonate). Mineral carbonation is the carbon sequestration approach with the greatest potential for sequestration capacity and permanency. Agricultural lands offer vast areas onto which such minerals can be applied, while benefiting crops. This work illustrates a technique to separate wollastonite-containing soils into different fractions. These fractions are characterized separately to determine organic and inorganic content, as well as to determine the chemical and mineral composition. The aim is to detect the fate of wollastonite in agricultural soils, and the fate of weathering/carbonation products in the soil. The soils used in the study were collected from soybean and potato farmlands in Southern Ontario, and from an experimental pilot plot. Soil fractionation was done using sieving, and soil fractions were analyzed by a calcimeter, X-ray diffraction, and loss-on-ignition. Acid digested samples were measured by Inductively Coupled Plasma Mass Spectrometry. Carbonates and wollastonite were enriched by fractionation.

Influence of electrolyte composition and pH on glyphosate sorption by cow-dung amended soil

This study investigated the pH-dependent relationship between glyphosate and soils before (NS) and after amendment with cow-dung, CD (SACD). Sorption isotherms were generated using batch equilibration techniques from CaCl2, KCl, CaSO4 and Ca(H2PO4)2 background electrolytes. Linear partition coefficients decreased with increase in pH in the order: CaCl2>KCl > CaSO4>Ca(H2PO4)2, which reflect both the effect of the inorganic anion in terms of competition and the cation in terms of bridging interactions. However, soil amendment with CD minimized the inhibitory effect of pH increase on glyphosate sorption. Variations in glyphosate sorption from CaCl2 and Ca(H2PO4)2 were attributed to fraction of hydrophilic contribution while variations in sorption from CaCl2 and KCl were attributed to Ca-bridging and ranged from 22 to 70% across the two soils. Estimated hydrophobic partitioning () systematically decreased with increasing soil solution pH from 36 to 3% and 5 to <1% in NS and SACD, respectively. Greater sorption in NS over SACD was partly attributed to higher phosphate level in SACD which is preferentially sorbed over glyphosate. This study noted CD application as soil amendment for agriculture could impede glyphosate sorption and facilitate its off-site leaching and contamination of surface and groundwater.

Effectiveness of Biochar Obtained from Corncob for Immobilization of Lead in Contaminated Soil.

Background.Recent studies have explored the potential for using biochar as a soil amendment in agriculture. However, it can also be used as a gentle remediation option for contaminant reduction. Biochar is a by-product obtained from the pyrolysis of biomass (organic matter). It is known for its long-lasting chemical properties, wide surface area values, and carbon-richness, which make it an efficient method for the immobilization of organic and inorganic contaminants such as heavy metals.Objective.The aim of the present study was to analyze the efficiency of biochar, obtained from the gasification of corncob, for the immobilization of lead in contaminated soils.Methods.In the present study, biochar from corncob was used as an amendment for soil contaminated with lead (extracted from the municipality of Malambo, Colombia) in order to estimate its ability to immobilize leaching lead. A comparison laboratory test applied a modified biochar produced with a 10% hydrogen peroxide chemical treatment. In addition, a pot experiment was done with both biochar by sowing seeds of Pennisetum clandestinum for 33 days. During this period, plant growth was measured for the different amendments of biochar concentrations.Results.Laboratory tests indicated that unmodified biochar obtained a maximum retention of 61.46% of lead, while the modified biochar obtained only 44.53% retention. In the pot experiments, the modified biochar indicated high germination and growth of seeds (up to 89.8%).Conclusions.Although the lead immobilization in soil was positive for both cases, the use of soil with high concentrations of lead (167.62 g/kg) does not indicate biochar's effectiveness for purposes of comparison with the current United States Environmental Protection Agency (USEPA) limit value (400 ppm for bare soil in urban play areas). Therefore, further studies are recommended using soil with lower lead concentration levels.Competing Interests.The authors declare no competing financial interests. One author is an employee of Pure Earth.

Valorization of sludge from the quartz industry as soil amendment and crop production

Europe is moving towards a resource efficient economy implementing as initiative the valorization of waste products. Hence, the use of waste sludge from the quartz industry as amendment in agriculture represents a promising alternative to recycle this by-product. The aim of this study was to test the suitability of the sludge from the quartz industry as soil amendment for agriculture. Four samples with different sewage sludge from the quartz industry and a control were investigated in a pot experiment with wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and sunflower (Helianthus annus L.) cultivated in a sandy soil classified as Inceptisol Ochrept Xerochrept from the Spanish province of Segovia during 2015 and 2016. The following treatments were applied: (1) 25% sewage sludge and 75% soil, (2) 50% sewage sludge and 50% soil, (3) 75% sewage sludge and 25% soil, (4) 100% sewage sludge and (5) 100% soil (control). The concentration of potentially toxic heavy metals was found to be below the critical limits imposed by regulations concerning the agronomic use of sludge. The application of this sludge also resulted in an improvement of soil properties, increasing a maximum of 31% the water content, 0.98% the oxidable carbon and providing a higher concentration of nutrients. In sludge treatments, the CE did not exceed the value of 2 dS cm−1 for sensitive field crops and for the pH the highest value achieved after the sludge application was 8.4 for the 100% quartz sludge treatment, which does not exceed the 8.5 established as limit for sodification risk. In relation to crop growth, the sludge treatment 25% sewage sludge and 75% soil presented positive results, being the height 0.715 m, 0.764 m and 1.16 m for wheat, barley and sunflower, respectively. The nature of this industrial sludge causes some deficiencies in crop yield when compared with the control, being the maximum difference in nitrogen and protein concentration between the sludge treatments and the control of 20%. These results suggest that the application of sludge from the quartz industry can potentially serve as soil amendment. The combination of this sludge with a supplementary nitrogen source could be further studied to improve the crop yield.

Impacts of long term copper exposure on abundance of nitrogen cycling genes and denitrification activity in pasture soils

Soils are the main source of nitrous oxide (N2O) emissions, with 60–70% of global N2O production due to the enhanced denitrification activity with elevated nitrogen (N) availability associated with agricultural intensification. The amendment of agricultural soils with biosolids, the residual product of wastewater treatment, has been used for several decades as an inexpensive source of organic matter and N. Biosolids also contain elevated levels of trace elements such as copper (Cu), which influence the activity of the bacterial enzyme nitrous oxide reductase (N2OR). We extracted DNA from a pasture soil 20 years after application of biosolid and Cu salts and used an environmental genomics approach (GeoChip) to evaluate broad changes in the abundance and structure of families of N-cycling genes. We then focussed on abundances of individual bacterial genes involved in sequential N-reduction (nirS, nirK, and nosZ). There was no relationship between total soil Cu concentrations and the different N-cycling gene families (GeoChip; P > 0.1). However, increasing Zn was associated with decreased nitrification (amoA) and dissimilatory N-reduction (napA and nrfA) gene-family abundances (P < 0.1). When focused on individual bacterial denification pathway genes (qPCR), nosZ (nitrous oxide reductase) was found to be sensitive to Cu concentrations. Moreover, the activity of the Cu-dependent enzyme N2OR is potentially affected by historical Cu concentrations found in these pasture soils. The results highlight the sensitivity of a few key functional taxa (nosZ type denitrifying bacteria) to long-term Cu exposure in soil, and how these effects can translate into alteration of wider N-cycling processes such as those affecting net N2O emissions.

Distribution trend of trace elements in digestate exposed to air: Laboratory-scale investigations using DGT-based fractionation

The use of digestate as amendment for agricultural soils has already been proposed as an alternative to mineral fertilizers or undigested organic matter. However, little information is available concerning the effect of digestate atmospheric exposure on trace elements speciation and, consequently, on their mobility and bio-accessibility when digestate is stored in open tanks or handled before land spreading. In this study, we investigated at laboratory-scale the effect of digestate aeration on the distribution of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and W using the diffusive gradients in thin films technique (DGT)-based fractionation. For this purpose, experiments were performed to assess the variation in distribution between the labile, soluble and particulate fractions over time in digested sewage sludge during passive and forced aeration. Results showed that aeration promoted a dissolution of Al, As, Co, Cr, Cu, Fe, Mn, Mo and Pb, suggesting a possible increase in their mobility that may likely occur during storage in open tanks or handling before land spreading. Labile elements’ fraction increased only during forced aeration (except for Fe and Mn), suggesting that their short-term bio-accessibility can increase only after significant aeration as the one assumed to occur when land spreading takes place.

Nutrient Source and Tillage Effects on Maize: II. Yield, Soil Carbon, and Carbon Dioxide Emissions

Core Ideas Industrial biotechnology waste as a soil amendment approximates farmer practice yields. Applying waste amendments significantly increased soil organic C compared with farmer practice. Using waste nutrients for agriculture and soil organic matter improves sustainability. Reuse of industrial biotechnology by‐products has become an important component of circular bio‐economies whereby nutrient‐rich wastes are returned to agricultural land to improve soil fertility and crop productivity. Heat‐inactivated spent microbial biomass (SMB) from the production of 1,3‐propanediol is an industrial fermentation by‐product with nutrients that could replace or supplement conventional fertilizers. Our objectives were to determine if SMB utilization as a soil amendment in agriculture could generate environmental benefits while meeting farmer yield expectations and assess the impact of SMB application on CO2 emissions. This study examined the replacement of typical farmer fertilizer practices with the application of SMB. In addition to yellow dent maize (Zea mays L. var. indentata) grain yield and aboveground biomass, soil organic carbon (SOC) was measured. The eddy covariance (EC) micrometeorological method was used to measure CO2 flux. Overall maize yields were positively correlated with increasing application rates of SMB. After two SMB applications, SOC increased by 45% on the SMB plot as compared with an increase of 11% on the farmer practice plot. The SMB‐treated plot also emitted more CO2 (794 g CO2 m−2 yr−1) compared with the farmer practice treatment (274 g CO2 m−2 yr−1). Results from this study provide information on the efficacy of waste product nutrient cycling in the soil–plant ecosystem that could improve productivity and sustainability.

Softening of drinking water by the pellet reactor - Effects of influent water composition on calcium carbonate pellet characteristics

Pellet softening of drinking water can provide aesthetic, socioeconomic and environmental benefits in areas with hard water. Calcium carbonate pellets are the main by-product from pellet softening and their characteristics determine their reuse potentials. We characterized pellets from a pilot-scale pellet reactor treating 16 water types at 8 Danish drinking water treatment plants to investigate the variations in pellet characteristics and how they depend on the influent water composition. The pellets consisted of up to 100% calcium as calcium carbonate, but contained often also impurities such as strontium, magnesium, iron and sodium, each contributing with up to 1.3% of the pellet mass. Other elements, including heavy metals, accounted for <0.04% of the pellet mass. The quartz sand seeding material contributed with up to 15% of the pellet mass and can be a barrier for pellet reuse. Therefore, replacing this with calcium carbonate (limestone) seeding material increases the pellet purity. Modelling the chemical speciation indicated that elements not forming carbonates (e.g. potassium and magnesium), are only incorporated into pellets to a limited extent. The concentrations of strontium, magnesium, manganese, iron and nickel in the pellets had a strong positive correlation with the influent water concentration. Consequently, the pellet purity increases if the concentration of these elements is reduced in the water before softening by other treatment technologies. Potassium, arsenic and zinc showed no or only a weak correlation. The pellets precipitated as calcite, and had a reactivity of ≤25.7% and a specific surface area of ≤0.32 m2/g, which limits the potential reuse as soil amendment in agriculture. The pellet mineralogy was independent of the investigated range of influent water quality and seeding materials. Including pellet characteristics when designing the softening process can improve pellet reuse, ultimately leading to a more environmentally sustainable drinking water supply.

Comparative studies of chemical crosslinking reactions and applications of bio-based hydrogels

Superabsorbent hydrogels are polymeric materials known for their ability to absorb and retain large amounts of water or aqueous solutions. Due to their unique properties, hydrogels have been useful in disposable diapers and other sanitary products, and in a range of other fields including agriculture and oral delivery of drugs, nutraceutical compounds or other bioactive molecules. The primary aim of this review is to provide an overview of several synthesis pathways for bio-based hydrogels by describing several chemical crosslinking methods and different ways of introducing new chemical functional groups to improve the absorbency of the polymers. In addition, bio-based superabsorbent hydrogels from proteins, carbohydrates and other biological molecules will be discussed, along with some of their applications in treating wastewater contaminated with heavy metals or as soil amendments in agriculture. Finally, some bio-based self-healing polymers and their respective applications will be covered in some details.

Effect of biochar, hydraulic residence time, and nutrient loading on greenhouse gas emission in laboratory-scale denitrifying bioreactors

Increased adoption of denitrifying bioreactors to mitigate nutrient export in agricultural drainage can improve water quality but also raises concerns about potential unintended consequences of widespread implementation. Greenhouse gas (GHG) emissions, especially as nitrous oxide (N2O) produced during denitrification, are of particular concern. To gain understanding of the variables controlling bioreactor GHG production, the effects of nutrient loading, hydraulic residence time, and biochar addition on emissions of N2O, methane (CH4), and carbon dioxide (CO2) were tested in 6550 cm3 laboratory columns. Biochar, an organic carbon pyrolysis product, was hypothesized to reduce GHG emissions, as has been reported with its use as an agricultural soil amendment. GHG fluxes were measured during 5-day trials using the closed dynamic chamber technique. The 36 combinations of three media types (woodchips, 10% biochar, and 30% biochar), three residence times (3, 6, and 12 h), and four influent formulations, all combinations of high and low nitrogen as nitrate (16.1 and 4.5 mg NO3-N L−1) and phosphorus as orthophosphate (1.9 and 0.6 mg PO4-P L−1) concentrations, were tested in triplicate. Treatment effects were assessed with linear mixed effects models. Biochar addition, particularly at the 30% rate, was found to increase N2O and CO2 emissions and the proportion of removed NO3-N released as N2O-N. However, quantified GHG flux rates were not environmentally concerning. Methane fluxes were negligible, and CO2 fluxes were not considered to increase net GHG emissions. Nitrous oxide fluxes normalized to surface area averaged 2.92 mg N2O-N m−2 d−1, and 98% of measured fluxes were within the range previously reported for woodchip bioreactors and considered acceptable.

Changes in root traits explain the variability of biochar effects on fruit production in eight agronomic species

Biochar (BC) application to soil could increase soil C sequestration, soil fertility, and crop production, which makes it an interesting soil amendment for organic agriculture. However, studies to date show a great variability in their results, depending on the plant species studied. Our hypothesis is that the different root responses of the species to the addition of BC may explain the high variability of BC effects on yield. We investigated the effects of addition of olive-tree pruning BC applied to soil at 5% w/w on soil properties, root morphology, and crop yield in a greenhouse pot experiment. We used eight species of agronomic interest: Brassica napus L., Capsicum annuum L., Cicer arietinum L., Glycine max L., Gossypium herbaceum L., Solanum lycopersicum L., Solanum melongena L., and Zea mays L. Addition of BC reduced soil bulk density and increased both soil water content and nutrient availability. BC addition had an influence on many plant traits as it increased the specific root length, specific leaf area, and leaf relative water content. Also, the BC addition increased aboveground biomass and fruit production. Interestingly, the increase in fruit production was positively correlated with the changes in specific root length. Our results support the hypothesis that the most responsive species to BC addition through changes in root traits may be those that increase more fruit production.