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Valorizing lignite waste into engineered nitro-humic fertilizer: Advancing resource efficiency in the era of a circular economy
Abstract
This study investigates using lignite waste as a carrier matrix for creating engineered nitro-humic fertilizer (NHF). The NHF is synthesized through an innovative ozone oxidation method and nitrogen enrichment. Agronomic efficiency was evaluated through maize growth responses, soil incubation experiments, and fertilizer performance, comparing NHF to commercial urea and NPK fertilizers. Nitrogen release patterns and kinetic models were studied to understand the nitrogen release mechanism of NHF. The engineered structure of NHF displayed globular-like, microporous, and heterogeneous properties, with a negative charge density of 48.85 mV and lower thermal stability of aliphatic carbons. The NHF exhibited a remarkable capability to increase water-holding capacity by up to 48% and extend the water-retention period by 57% during 30 d of soil application. NHF significantly reduced soil urease enzyme activity by more than two-fold. It exhibited a longer nitrogen release period (77 d) with a slow-release pattern, releasing 71.75% of total nitrogen compared to 88.5% in 14 d for urea. The simple Elovich model accurately predicted NHF's nitrogen release kinetics (R2 = 0.9943), identifying Fickian diffusion-based controlled release. Applying NHF improved multiple aspects of maize growth: height, stem diameter, biomass, root weight, leaf area, SPAD value, and leaf nitrogen concentration. Total chlorophyll, carotenoid, and nitrogen uptake also greatly increased compared to the control sample. NHF exhibited superior nitrogen use efficiency (41.5%) and agronomic fertilizer efficiency (36.22%) compared to urea and even surpassed commercial NPK fertilizers. Generally, the produced NHF is an eco-friendly alternative to slow-release fertilizers, offering the advantages of humic substances and nitrogen fertilizers.
... As an amide enzyme, urease is positively correlated with the number of soil microorganisms [31], Li et al. also showed that urease is positively correlated with the number of soil microorganisms. organic matter content [32], total nitrogen, and available nitrogen content [33], and its activity often represents the nitrogen status of the soil [34]. This result is consistent with previous studies. ...
... In contrast, researchers have investigated whether the recycling of animal and vegetable waste is a feasible means to achieve a more natural production of agricultural products. Novel approaches are constantly being developed and tested, highlighting the possibility of adopting new methods to convert organic waste streams into value-added products like biochar (Silva et al., 2022), nitro-humic fertilizers (Sarlaki et al., 2023), and artificial humic acids, such as lignin-rich biogas digestate (Sarlaki et al., 2024). ...
Slow-release fertilizers are sustainable alternatives to soil nutrition that can effectively enhance agricultural productivity. In this study, we formulated slow-release organomineral fertilizers using spent coffee grounds (SCG) impregnated with triple superphosphate (TSP). The effects of the composition of the fertilizer on pellet resistance and P release capacity were evaluated, along with heat treatment at different temperatures and times. The pellets with 10 g sugarcane molasses and 2.5 g TSP per gram of SCG, dried at 100 °C, presented the best mechanical resistance, releasing about 90% P in 13.8 h. The release kinetics of these pellets followed the Korsmeyer-Peppas model, controlled by Fickian diffusion. The fertilizer thermally treated at 400 °C for 30 min was classified as a slow-release fertilizer, as it released 90% P in 793.3 h. Thus, the partial carbonization of biomass promoted P adsorption to the surface of the porous matrix of the pellets, allowing the slow release of nutrients. Overall, we found that pelletized OMFs can be used as sustainable and inexpensive fertilizers derived from waste biomass; thus, their application can contribute to eco-friendly agricultural practices.
Index terms:
Extrusion; release kinetics; thermal treatment; fickian diffusion; sustainable agriculture.
... Their structure, shape and particle size are dynamic and influenced by the type of starting biomass, water content and soil structure, and environmental conditions (e.g., concentration, pH, ionic strength, or redox potential etc.) (Klučáková 2018). Soil amendments incorporating artificial humic substances are becoming increasingly recognized for their environmentally beneficial properties as biostimulants and soil conditioners (Pukalchik et al. 2019;Lee et al. 2019;Sarlaki et al. 2023b). The application of artificial humic substances to soil has been shown to improve plant growth, but the extent is inconsistent and depends on a number of factors such as the source of the humic substances, the environmental growing conditions, the type of plant being treated, and the manner of application (Rose et al. 2014). ...
Hydrothermal carbonization (HTC) converts wet biomass into hydrochar and a process liquid, but aromatic compounds in the products have been reported as a roadblock for soil applications as they can inhibit germination, plant growth, and soil microbial activity. Here, we compared HTC and hydrothermal humification (HTH) of cow manure digestate while varying the initial alkaline content by adding KOH. HTH converted 37.5 wt% of the feedstock to artificial humic acids (A-HAs) found in both solid and liquid, twice that of HTC. HTH reduced phenolic and furanic aromatic compounds by over 70% in solids and 90% in liquids. The A-HAs in HTH resemble natural humic acids (N-HA), based on FTIR, UV–vis spectra, and CHN and XRD analysis. The HTH liquid possesses 60% higher total organic carbon (TOC) than HTC. Although one-third of TOC can be precipitated as A-HA, a high TOC concentration remains in the liquid, which is shown to be mainly organic acids. Therefore, we also evaluated the HTC and HTH liquids for anaerobic biomethane production, and found that compared to the original cow manure digestate, the HTH liquids increased methane yield by 110.3 to 158.6%, a significant enhancement relative to the 17.2% increase seen with HTC liquid. The strong reduction in organic acids during biogas production from HTH liquid indicates the potential for converting soluble byproducts into methane, while maintaining high A-HAs levels in the solid product.
Graphical Abstract
... Consequently, there is a growing reliance on chemical fertilizers, which now account for over 70% of agricultural and food production (Rodríguez-Espinosa et al., 2023). The main drawbacks of chemical nitrogenous fertilizers include low nitrogen use efficiency by plants (less than 30%), high emissions of greenhouse gases, high production costs, and negative impacts on soil organic matter content, microbial population, and diversity (Sarlaki et al., 2023b). Farmers are ramping up their agricultural activities and relying heavily on chemical fertilizers to boost their income from farming without considering the negative impact on the environment. ...
Hydrothermal carbonization (HTC) solid and liquid products may inhibit seed germination, necessitating post-treatment. The hydrothermal humification (HTH) method addresses this drawback by transforming inhibitory compounds, such as aromatics, into artificial humic acids (AHAs) and artificial fulvic acids (AFAs). This study introduces a novel approach by investigating the substitution of the commonly used alkaline agent in HTH, KOH, with hydrated lime to develop cost-effective hydrothermal fertilizers from sugar beet pulp, enriching them with AHAs. It assesses the effects of lime on AHA production and soluble organic compounds compared to KOH. The results indicate that lime significantly reduces furans (from 560 to 3.15 mg/kg DM in solid and from 344 to 3.86 mg/L in process liquid) and boosts sugars and organic acids, especially lactic acid (from 4.70 to 65.82 g/kg DM in solid and from 4.05 to 22.89 mg/L in process liquid), increasing hydrochar yield (68.8% with lime vs. 27.4% with KOH). Despite the lower AHA production with lime compared to KOH (3.47% vs. 15.50%), lime-treated hydrothermal products are abundant in calcium and magnesium, boasting a pH of 7. This property presents a safer and more efficient alternative to hydrothermal fertilizers. The characterization of AHAs aligns with standard and natural humic substances, while lime-assisted HTH products, applied at a level of 0.01% w/w, could significantly enhance wheat growth and nutrient uptake compared to the control group. Importantly, these products show no toxicity on Daphnia magna, underscoring their potential for sustainable agriculture.
Conventional nitrogen (N) fertilizers particularly urea mineralized quickly in soil. Without sufficient plant uptake, this rapid mineralization favors the heavy N losses. Lignite is a naturally abundant and cost-effective adsorbent capable of extending multiple benefits as a soil amendment. Therefore, it was hypothesized that lignite as an N carrier for the synthesis of lignite-based slow-release N fertilizer (LSRNF) could offer an eco-friendly and affordable option to resolve the limitations of existing N fertilizer formulations. The LSRNF was developed by impregnating urea on deashed lignite and pelletized by a mixture of polyvinyl alcohol and starch as a binder. The results indicated that LSRNF significantly delayed the N mineralization and extended its release to >70 days. The surface morphology and physicochemical properties of LSRNF confirmed the sorption of urea on lignite. The study demonstrated that LSRNF also significantly decreased the NH 3-volatilization up to 44.55%, NO 3-leaching up to 57.01%, and N 2 O-emission up to 52.18% compared to conventional urea. So, this study proved that lignite is a suitable material to formulate new slow-release fertilizers, suiting to alkaline calcareous soils favorably where N losses are further higher compared to non-calcareous soils.
The farmland in Yinchuan is composed of sierozem soil, which is characterized by high sand content and low organic matter content, resulting in poor water-holding capacity and weak soil structure. Humic acid is a natural organic polymer soil amendment. It is critical to study how humic acid affects soil water infiltration in sierozem soil at the microlevel. A one-dimensional vertical infiltration experiment was conducted to explore how adding different amounts of humic acid (0, 1%, 2%, 3% and 4%) affected the infiltration characteristics and hydraulic parameters of the sierozem soil. The results revealed that the wetting front and cumulative infiltration decreased with the increase in humic acid addition. When the infiltration time was 90 min, the wetting front of the 1%, 2%, 3% and 4% treatments was 6.50%, 10.00%, 15.00% and 21.00% lower than CK (0 for CK), and the cumulative infiltration volume was 4.50%, 11.14%, 18.42% and 23.60% lower than CK, respectively. Among the three infiltration models created by Philip, Horton and Kostiakov, the Kostiakov model (R2 > 0.95) could more accurately describe the soil water infiltration process in the study area. After infiltration, the moisture content of each soil layer increased with the increase in humic acid, which improved the water-holding capacity of the sierozem soil. Using Hydrus-1D to calculate soil hydraulic parameters, we found that the humic acid addition affected the hydraulic parameters. With the increase in the amount of humic acid addition, the retention water content θr and saturated water θs were positively correlated with the humic acid addition amount and negatively correlated with the saturated water conductivity Ks and the reciprocal of air-entry α. The results showed that humic acid could increase the water-holding capacity of soil and improve the rapid water loss and poor water-holding capacity of sierozem soil.
Agriculture accounts for 12% of global annual greenhouse gas (GHG) emissions (7.1 Gt CO2 equivalent), primarily through non-CO2 emissions, namely methane (54%), nitrous oxide (28%), and carbon dioxide (18%). Thus, agriculture contributes significantly to climate change and is significantly impacted by its consequences. Here, we present a review of technologies and innovations for reducing GHG emissions in agriculture. These include decarbonizing on-farm energy use, adopting nitrogen fertilizers management technologies, alternative rice cultivation methods, and feeding and breeding technologies for reducing enteric methane. Combined, all these measures can reduce agricultural GHG emissions by up to 45%. However, residual emissions of 3.8 Gt CO2 equivalent per year will require offsets from carbon dioxide removal technologies to make agriculture net-zero. Bioenergy with carbon capture and storage and enhanced rock weathering are particularly promising techniques, as they can be implemented within agriculture and result in permanent carbon sequestration. While net-zero technologies are technically available, they come with a price premium over the status quo and have limited adoption. Further research and development are needed to make such technologies more affordable and scalable and understand their synergies and wider socio-environmental impacts. With support and incentives, agriculture can transition from a significant emitter to a carbon sink. This study may serve as a blueprint to identify areas where further research and investments are needed to support and accelerate a transition to net-zero emissions agriculture.
Nitrogen (N) is an essential plant macro-nutrient for crop sustainability and productivity. Substantial quantities of N fertilizers are being applied in soil, but only about 33% is utilized by the plants. Its availability in soil varies to a great extent in terms of time and space. Plant root systems should efficiently respond to fluctuating N by tailoring root growth and development. However, N fertilizer production consumes massive energy resource, and excessive application has negative consequences on the environment and human health. Therefore, innovative solutions are imperative to enhance crop yields and N use efficiency (NUE) simultaneously, while maintaining and/or reducing N application amount. Crop NUE is a complex attribute, because it is controlled by numerous genetic as well as environmental factors interact to govern the mechanisms involved in N sensing,
uptake, translocation, assimilation, and remobilization in plants. Hence, a better understanding of these mechanisms is a key factor for improving NUE in cropping systems. In this review, we discussed the molecular, biochemical, and enzymatic
mechanisms involved in NUE in crop plants, ways to increase NUE through the identification of plant factors with special consideration of their interaction, and different management strategies. In addition, adaptation of classical approaches, i.e., root architecture studies, quantitative trait loci (QTLs), and selection of genes for better NUE, are briefly discussed. Broadly, from root uptake to accumulation of N assimilates in various plant tissues, an array of physiological mechanisms is involved
which is still not fully understood. Moreover, employing an integrated approach by combining expertise from fundamental and applied investigations in crop sciences may add further to available knowledge regarding crop N utilization
Food security relies on nitrogen fertilizers, but its production and use account for approximately 5% of global greenhouse gas (GHG) emissions. Meeting climate change targets requires the identification and prioritization of interventions across the whole life cycle of fertilizers. Here we have mapped the global flows of synthetic nitrogen fertilizers and manure and their corresponding GHG emissions across their life cycle. We have then explored the maximum mitigation potential of various interventions to reduce emissions by 2050. We found that approximately two-thirds of fertilizer emissions take place after their deployment in croplands. Increasing nitrogen-use efficiency is the single most effective strategy to reduce emissions. Yet this should be combined with decarbonization of fertilizer production. Using currently available technologies, GHG emissions of fertilizers could be reduced up to approximately one-fifth of current levels by 2050.
Vermicompost was used for humic acid (HA) preparation, and the adsorption of aflatoxin B1 (AFB1) was investigated. Two forms of HA were evaluated, natural HA and sodium-free HA (SFHA). As a reference, a non-commercial zeolitic material was employed. The adsorbents were characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), energy-dispersive X-ray spectroscopy (EDS), zeta potential (ζ-potential), scanning electron microscopy (SEM), and point of zero charge (pHpzc). The adsorbent capacity of the materials when added to an AFB1-contaminated diet (100 µg AFB1/kg) was evaluated using an in vitro model that simulates the digestive tract of chickens. Characterization results revealed the primary functional groups in HA and SFHA were carboxyl and phenol. Furthermore, adsorbents have a highly negative ζ-potential at the three simulated pH values. Therefore, it appears the main influencing factors for AFB1 adsorption are electrostatic interactions and hydrogen bonding. Moreover, the bioavailability of AFB1 in the intestinal section was dramatically decreased when sorbents were added to the diet (0.2%, w/w). The highest AFB1 adsorption percentages using HA and SFHA were 97.6% and 99.7%, respectively. The zeolitic material had a considerable adsorption (81.5%). From these results, it can be concluded that HA and SFHA from vermicompost could be used as potential adsorbents to remove AFB1 from contaminated feeds.
Cropland is a main source of global nitrogen pollution1,2. Mitigating nitrogen pollution from global croplands is a grand challenge because of the nature of non-point-source pollution from millions of farms and the constraints to implementing pollution-reduction measures, such as lack of financial resources and limited nitrogen-management knowledge of farmers3. Here we synthesize 1,521 field observations worldwide and identify 11 key measures that can reduce nitrogen losses from croplands to air and water by 30–70%, while increasing crop yield and nitrogen use efficiency (NUE) by 10–30% and 10–80%, respectively. Overall, adoption of this package of measures on global croplands would allow the production of 17 ± 3 Tg (1012 g) more crop nitrogen (20% increase) with 22 ± 4 Tg less nitrogen fertilizer used (21% reduction) and 26 ± 5 Tg less nitrogen pollution (32% reduction) to the environment for the considered base year of 2015. These changes could gain a global societal benefit of 476 ± 123 billion US dollars (USD) for food supply, human health, ecosystems and climate, with net mitigation costs of only 19 ± 5 billion USD, of which 15 ± 4 billion USD fertilizer saving offsets 44% of the gross mitigation cost. To mitigate nitrogen pollution from croplands in the future, innovative policies such as a nitrogen credit system (NCS) could be implemented to select, incentivize and, where necessary, subsidize the adoption of these measures. A meta-analysis of 1,521 field observations from the past two decades led to the identification of 11 key measures to cost-effectively mitigate nitrogen pollution from global croplands.
Poor organic matter and nitrogen (N) deficiency along with salinity in arid and semiarid region soils are major hurdles to optimization of cereal's yield. In different cereals, maize productivity is significantly decreased due to less availability of N in low organic matter soils. Scientists suggest the incorporation of organic fertilizers to overcome this issue. That’s why the current study was conducted to explore the effectiveness of chemically produced nitrate blended acidified carbon (NBC). There were 3 levels of NBC i.e., 0, 0.50 and 1.00% applied under naturally normal and saline soils having EC 2.75 and 6.19 dS/m respectively. Results showed that the addition of 1.00NBC was significantly better compared to 0NBC for improvement in maize growth attributes i.e., root (32.86 and 77.84%) and shoot (74.17 and 67.57%) length, shoot fresh (53.98 and 97.42%) and dry weight (53.20and 84.20%), root dry (45.97 and 53.66%) and fresh weight (45.62 and 25.14%) in normal and saline conditions respectively. A significant enhancement in chlorophyll a, b, total and carotenoids of maize leaves also validated the imperative role of 1.00NBC than 0NBC in saline and normal soil. Application of 1.00BC also significantly decreases leaves electrolyte leakage and Na concentration in root and leaves over 0NBC in saline soils. In conclusion, 1.00NBC is an effective amendment to improve maize growth in saline soil. More investigations are suggested on different cereal crops under variable agroclimatic zones to declare 1.00NBC as the most effective amendment for alleviation of salinity stress.
Two polyester-lignite composite coated urea slow-release fertilizers (SRFs; Poly3 and Poly5) were developed and their physicochemical properties were studied. Both these SRFs significantly (p < 0.05) extended the urea release compared to uncoated urea; Poly3 and Poly5 by 117 and 172 h, respectively. The urea release characteristics of Poly5 were further enhanced by linseed oil application (Poly5-linseed). The SEM images demonstrated the coatings were in contact with the urea and encase urea particles completely with the average coating thickness of 167.2 ± 15 µm. The new interactions between polyester and lignite in the composite coating were confirmed by the FTIR analysis. Polyester-calcium carbonate (Polyester-CaCO 3 ) coated SRFs (Calc3 and Calc5) were developed using CaCO 3 as a filler in place of lignite and the urea dissolution rate was compared with Poly3 and Poly5. The urea release times for the polyester-CaCO 3 formulations, 48 and 72 h, were significantly ( P < 0.05) lower than the polyester-lignite formulation, showing that lignite imparted greater control over release time than CaCO 3 . Findings from this work showed that polyester-lignite composites can be used as a coating material for SRFs.
Graphical abstract
This study was launched to test organic materials in the form of humic acids (HA) applied to soil to improve the effect of nitrogen on maize, and to determine an optimal dose of HA, which will be ecologically safe and will counteract potential negative (phytotoxic) influences of excessive nitrogen fertiliser doses, on two soils with different textural composition. The maize plants grown on the loamy sand were characterised by a higher value of the SPAD leaf greenness index, yields, and a lower content of total-N and sulphate sulphur in maize. Urea, and especially UAN, promoted higher SPAD leaf greenness index values during the stem elongation stage and particularly during the tassel emergence stage. The effect of urea on maize yields was positive on both soils, but UAN had a positive effect on this parameter only on the loamy sand. HA tended to increase the SPAD leaf greenness index. The impact of HA on plant height and yields (especially medium dose) was generally positive. However, a negative effect of the interaction of HA with UAN on the plant height and maize yield on the sand was observed. HA caused an increase in the total-N content, and their highest dose also decreased the sulphate sulphur content in maize. The application of HA to soil has a positive influence on the growth and development of plants and can create positive effects by mitigating adverse consequences of intensive agricultural production in the natural environment.
Weathered coal is known to have potential inhibitory effects on urease activity, thus reducing the loss of nitrogen from fertilizer such as ammonia. This means that it can be used as a urea enhancer to promote urea utilization efficiency. However, the variation in its composition and structure has impeded the optimal utilization of this resource. In this study, we collected Chinese weathered coal from six representative geographical locations and analyzed its elemental and substance composition, as well as determined its chemical structure via Fourier transform infrared spectroscopy and investigated its effects on urease (soybean meal) activity. The results showed evident variation in the composition and structure among the different weathered coal samples, especially in the pH values, humic acid and ash content, and aromaticity. All six weathered coal samples significantly inhibited urease activity, and the inhibitory effect was enhanced with the elevated proportion of weathered coal introduced to urea. When the additive proportion of weathered coal increased, the weathered coal, characterized as having a higher humic acid content and a more aliphatic structure, showed a more rapid increase in the urease activity inhibition rate, while there was only a slight effect when the weathered coal had a low humic acid content and high atomicity. Therefore, the former type of weathered coal was more sensitive to the additive proportion. Furthermore, there was no consistent rule when the same proportion of weathered coal from different geographic locations was blended into urea, which might be attributable to other unexplored factors.
Globally, nitrogen (N) fertilizer demand is expected to reach 112 million tonnes to support food production for about 8 billion people. However, more than half of the N fertilizer is lost to the environment with impacts on air, water and soil quality, and biodiversity. Importantly, N loss to the environment contributes to greenhouse gas emissions and climate change. Nevertheless, where N fertilizer application is limited, severe depletion of soil fertility has become a major constraint to sustainable agriculture. To address the issues of low fertilizer N use efficiency (NUE), biochar-based N fertilizers (BBNFs) have been developed to reduce off-site loss and maximize crop N uptake. These products are generally made through physical mixing of biochar and N fertilizer or via coating chemical N fertilizers such as prilled urea with biochar. This review aims to describe the manufacturing processes of BBNFs, and to critically assess the effects of the products on soil properties, crop yield and N loss pathways.
Graphical Abstract
Based on weathered coal (WC), a new type of nitrogen-enriched weathered coal fertilizer (NCF) was synthesized herein using hydrogen peroxide and urea in a closed container. Inductively coupled plasma mass spectrometry, elemental analysis, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Contact angle, Zeta potential and X-ray diffraction (XRD) measurements were performed; the obtained results showed that NCF has potential slow-release nitrogen properties. Additionally, the FTIR and XPS measurements revealed that NCF has various oxygen-containing active functional groups along with nitrogen-containing groups. A soil leaching test and the release kinetic model fitting of total nitrogen showed that NCF released nitrogen more slowly and over a longer time than urea, with nitrogen still being released after 70 days. Further, a mechanism study was performed, which revealed that NCF has a dual release performance that is similar to that of biochar and “dissolved black nitrogen.” Moreover, the total nitrogen release behavior of NCF was dominated by the multi-effects of the coal carbon carrier, including electrostatic attraction, the unconventional formation of hydrogen bonds, and decomposition of the nitrogen-containing groups. Furthermore, the application of NCF in both soil types (Lou and Loessal soil) stimulated the germination rate of spinach seeds and improved the chloroplast pigment content as well as the nutritional quality of spinach leaves. These results suggest that abandoned weathered coal may be fully utilized in the mining area and that NCF may have promising potential in improving plant quality and sustainable agriculture applications.
Graphical Abstract
Sewage sludge generated in the wastewater treatment process is a waste material and a serious environmental nuisance. Due to its specific properties, the management and final disposal of sewage sludge is a considerable problem also in Poland. Ozonation of sewage sludge is the most commonly used process based on the use of oxidizing agents for stabilization of the waste. This process results in substantial reduction of the sludge volume and simultaneous production of small amounts of toxic by-products. Despite the effectiveness of ozone in sanitation and reduction of sludge amounts and in improvement of many parameters, still little is known about the use of ozonated sewage sludge for agricultural purposes, e.g., fertilization of arable crops. Therefore, the present study was an attempt to evaluate the effect of ozone-stabilized sewage sludge on maize development in initial stages of growth in pot experiment conditions. We analyzed the effect of ozone-stabilized sewage sludge in soil on dry matter yields of aboveground parts of maize. We also conducted physiological measurements of chlorophyll content, fluorescence, and exchange. Additionally, the content of macro- and microelements and toxic heavy metals in aboveground maize biomass was determined. The ozone-stabilized sewage sludge exerted a positive impact on all maize parameters in the initial stage of growth. Compared to the control, plants fertilized with this type of sludge were characterized by a 50% higher yield of aboveground biomass and over 80% higher content of chlorophyll. Furthermore, the content of most macro- and microelements in the aboveground biomass was generally higher in plants fertilized with the ozonated sludge than in plants from the other experimental variants. The chlorophyll fluorescence and gas exchange parameters in plants fertilized with ozonated sludge were improved. No excessive accumulation of Pb and Cd was detected. The present results have confirmed that ozone-stabilized sewage sludge can be used for cultivation of agricultural plants, as it improves utilization of deposited nutrients. The improved bioavailability of nutrients was associated with ozonation-induced initial degradation of organic matter and release of deposited plant nutrients.
Humic acids (HA) are organic molecules that play essential roles in improving soil properties, plant growth, and agronomic parameters. The sources of HA include coal, lignite, soils, and organic materials. Humic acid-based products have been used in crop production in recent years to ensure the sustainability of agriculture production. Reviewed literature shows that HA can positively affect soil physical, chemical, and biological characteristics, including texture, structure, water holding capacity, cation exchange capacity, pH, soil carbon, enzymes, nitrogen cycling, and nutrient availability. This review highlights the relevance of HA on crop growth, plant hormone production, nutrient uptake and assimilation, yield, and protein synthesis. The effect of HA on soil properties and crops is influenced by the HA type, HA application rate, HA application mode, soil type, solubility, molecular size, and functional group. This review also identifies some knowledge gaps in HA studies. HA and its application rate have not been tested in field experiments under different crops in rotation, nitrogen fertilizer forms, sites and climatic conditions. Furthermore, HA chemical and molecular structures, their water and alkaline soluble fractions have not been tested under field experiments to evaluate their effects on crop yield, quality, and soil health. The relationship between soil-plant nutrient availability and plant nutrient uptake following HA application should also be further studied.
BACKGROUND
Humic acid (HA)‐enhanced urea (HAU) is the top‐selling efficiency‐enhanced urea in China. Comprehensive investigation into the structure and efficacy of HA complex formation with urea (HACU) – the main reaction product during HAU's production – is required to clarify the reaction mechanism between HA and urea, and to provide guidance for the development of high‐efficiency HAU.
RESULTS
HACU showed discrepant structural and compositional features from raw HA. Nitrogen (N) content in HACU was 7.3 times greater than that of HA. Several high‐resolution analytical methods showed a sharp increase of ammonia in the gaseous product during HACU pyrolysis, suggesting that urea contributed N to HACU. HACU was characterized with significantly fewer carboxyl groups than in raw HA, implying that the carboxyl group was the main group in HA to participate in the reaction between HA and urea. The presence of amide‐N in HACU verified the structure of the reaction product. Furthermore, both HACU and HA could enhance the biomass in hydroponically grown maize seedlings, but the highest stimulation for HACU came about when its carbon concentrations were 50–100 mg L⁻¹, higher than the optimal carbon concentration for HA (25 mg L⁻¹), attributed to the lower carboxyl group content for HACU to some extent.
CONCLUSION
During HAU's production, reaction with N derived from urea to form amide‐N decreased the carboxyl groups in HA, leading to higher concentrations for HACU required to achieve the similar bioefficacy of HA. © 2021 Society of Chemical Industry.
Five coal samples obtained from Chinese coal-producing areas were oxidized by hydrogen peroxide (H 2 O 2 ), and humic acids (HAs) were derived from original coal and its oxidizition samples. HAs were characterized by physical and chemical methods, between which was also comparison. Yield, ash, aromaticity, molecular weight and functional group of HAs showed variance between original coals. While, yield, molecular weight, and the quantity of oxygen-containing groups of HAs increased more from coals oxidized with H 2 O 2 . However, the increase of oxygen-containing functional groups depended on original coals. For Yimin lignite, the oxidation of H 2 O 2 could obviously improve the carboxyl group content of HAs, thus promoting the adsorption of nitrogen. This study demonstrated that oxidation of coal by using H 2 O 2 was one pretreatment way to obtain and modify HAs which could be used as prerequisite and functional material in agricultural field.
Nitrogen use efficiency enhancement is an important approach to obtain sustainable agriculture. Engineered biochar is considered as a super carrier to produce high-quality slow-release fertilizer. The purpose of this study was to compare nitrate and ammonium release using three treatments (i.e., MgCl2-modified biochar-based slow-release fertilizer (MBSRF), enriched modified biochar (EMBC), and chemical fertilizer (ammonium nitrate: AN)) and to analyze their effects on water retention, nitrogen use efficiency, and Zea mays L. growth. The treatments were prepared, and nitrate and ammonium release were determined. A pot experiment was performed with four treatments (control, MBSRF, EMBC, and AN), and the treatments’ impacts on selected parameters were investigated. Soils treated with EMBC and MBSRF retained more water than those treated with AN and the control treatment. The nitrate and ammonium release of MBSRF was slower and about 2.5 and 1.5 times lower than that of AN. MBSRF effectively increased plant height (20.1, 11.7, 37.1 %), shoot dry weight (24.2, 23.3, 44.0 %), root dry weight (29.9, 24.1, 48.8 %), chlorophyll content (9.43, 8.01, 13.6 %), and leaf area (24.8, 21.0, 30.4 %) in comparison to the AN, EMBC, and control treatments, respectively. Furthermore, the highest soil and plant nitrogen content and nitrogen use efficiency were associated with the MBSRF treatment. In conclusion, the use of MgCl2-modified biochar is promising in the synthesis of nitrogen slow-release fertilizer, and MBSRF can be used as a novel nitrogen slow-release fertilizer for increasing nitrogen use efficiency and improving corn growth.
In this study, humic substances were extracted from lignite of Zarand coalfields, Kerman, Iran, using a stirred batch reactor. A membrane ultrafiltration system was used to purify humic acids (HAs) from lignite-derived alkaline extracts obtained from the reactor. Gravimetric analysis along with several analytical methods including CHNOS, UV-Vis, FT-IR, ICP-OES and SEM were utilized to investigate the characteristics of the purified HAs. Gravimetric analysis showed that the purity of HA purified from membrane concentrated humates was higher than 95 %. CHNOS elemental analysis indicated the higher stability and condensation degree of the purified HA compared to the commercially available HAs. The ratios of E 4 /E 6 , E 2 /E 3 , and ΔlogK obtained from UV-Visible spectroscopy revealed that a purified HA had a higher molecular weight, aromaticity, and humification degree in comparison with commercial HAs. Furthermore, the peaks observed in the FT-IR analysis showed that HA had an aromatic structure. The very low concentrations of heavy metals and inorganic element contaminants observed by ICP-OES spectrometry showed a proper performance of the HA membrane purification. These results along with the results of SEM analysis showed the acceptable characteristics of purified HA from the lignite coal for agricultural and industrial applications.
This study evaluated the effectiveness of unmodified and modified biochar derived from Pisum sativum peels waste biomass as an adsorbent of copper (II) from aqueous medium under batch adsorption experiments at room temperature. The unmodified biochar was chemically modified by ozone oxidation followed by reaction with ammonium hydroxide and labeled as Pea-B and Pea-BO-NH2. The adsorption behavior of Cu2+ ions and the effect of required experimental parameters as initial Cu2+ ions concentrations, biochar dose, reaction time, and pH were intensively studied. The unmodified biochar (Pea-B) and modified biochar (Pea-BO-NH2) had significant copper (II) adsorption capacities of 126.25 and 156.25 mg/g, respectively, with 100% removal efficiency. The prepared biochars were characterized by Brunauer, Emmett and Teller (BET), Barrett, Joyner, Halenda (BJH), Scan Electron Microscope (SEM), Fourier Transform Infrared (FTIR), Thermal gravimetrical analysis (TGA) and Energy Dispersive Spectroscopy (EDAX) analyses. EDAX and FTIR analyses proved that amino groups were successfully formed onto the modified biochar surface. The data of adsorption experiments at equilibrium were studied by using various isotherm models as well as the error function equations were applied to the data of isotherm models. The analysis of the experimental data of Pea-B and Pea-BO-NH2 biochars showed that the best fit isotherm models were the Langmuir and Tempkin isotherm models, respectively. The adsorption rate of copper (II) was analyzed using different kinetic models and the pseudo-second-order was expressed as the most appropriate model for both Pea-B and Pea-BO-NH2 biochars.
Long‐term stockpiling of soil salvaged from oil sands operations often leads to the deterioration of soil quality and poor reclamation results for disturbed land. This study assessed the efficacy of organic amendments in improving the quality and productivity of long‐term stockpiled salvaged soil in Canada's Alberta oil sands region (AOSR). Dry soil samples (4.2 kg) from a 24‐yr‐old stockpile were placed into 5‐L pots and amended with biochar, humalite, peat, and 50:50 mixtures of biochar and peat (BCP) and biochar and humalite (BCH) at rates corresponding to 0, 6.55, 13.1, and 26.2 g C kg⁻¹ soil. The pots were seeded with barley (Hordeum vulgare L.), fertilized, and placed in a growth chamber. Plants were allowed to grow for three crop cycles of 45 to 59 d each and harvested at the end of each cycle. Results showed that biochar and peat increased dry matter yield (DMY) by 38 and 40%, respectively, compared with the unamended soil. Humalite produced the highest N and P concentrations in plant tissue, but this did not translate to an increase in DMY. Biochar and peat offer the greatest promise for improving the productivity of long‐term stockpiled salvaged soil, thereby enhancing the success of reclamation of disturbed sites.
Mechanochemical activation of coal is commonly employed in industry. However, even the simplest solid-phase reactions, such as neutralization of humic acids in brown coal, remain insufficiently studied. The hypothesis regarding the occurrence of mechanochemical neutralization under local hydrothermal conditions for humic acids in brown coal has been tested in this study. 3D modelling of the “block–interlayer” system (where coal particles are separated by air interlayers saturated with water vapor) was used. The 3D model showed that the permittivity is expected to rise from 14 to 16% as the moisture content in the system increases from 12 to 15%. The actual permittivities of coal with different moisture contents have been measured by dielectric spectroscopy. In the real system, the permittivity increases more than threefold as the moisture content rises from 12 to 15%. This increase is much greater than the calculated one, demonstrating that the phase containing unbound water appears in the system at a moisture content of ∼12–13% and may exert various effects on the solid-phase reaction. There is a correlation between the moisture content, permittivity, and predominant mechanisms of the reaction between the organic matter in brown coal and sodium percarbonate (a reagent simultaneously containing the alkaline and peroxidic components). The reactions between brown coal and alkaline reagents proceed under local hydrothermal conditions. Both the alkaline and peroxidic components of sodium percarbonate participate in the solid-phase reaction between brown coal and sodium percarbonate. The emergence of unbound water in coal significantly inhibits the oxidation reaction.
BACKGROUND
The utilization rate of urea‐N in fertilizer plays a very important role in agricultural production and environmental protection. Humic acid urea (HAU) and polyaspartic acid urea (PAU) are two similar synergistic nitrogen fertilizers.
METHODS
Fourier‐transform infrared spectroscopy (FTIR), X‐ray powder diffraction (XRD) and carbon‐13‐nuclear magnetic resonance (¹³C‐NMR) were used to determine the loading of urea‐N into humic acid (HA) and polyaspartic acid (PA). Thermal stability and physical adsorption properties of HAU and PAU were assessed by thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface measurement. The soil incubation experiment was conducted to investigate the effects of HAU and PAU on nitrogen transformation and gaseous nitrogen loss compared with commercial urea.
RESULTS
Nitrogen transformation from HAU and PAU was slowed down compared with urea. After 90 days of incubation, HAU and PAU reduced the cumulative ammonia (NH3) volatilization (by 9.70% and 6.30%, respectively) and nitrous oxide (N2O) emission (by 40.48% and 43.00%, respectively) from soil compared with the urea‐alone treatment.
CONCLUSION
HAU and PAU could improve the nitrogen use efficiency. © 2020 Society of Chemical Industry
Agriculture’s most pressing challenge is raising global food production while minimising environmental degradation. Nutrient deficiencies, principally nitrogen (N), limit production requiring future increases in fertiliser use and risk to proximal non-agricultural ecosystems. We investigated combining humate with urea, globally the most widely used N-suppling fertiliser, in a four-year field study. Humate increased pasture yield by 9.8% more than urea and significantly altered soil microbial diversity and function. Humate increased N retention suggesting microbial sequestration may lower N leaching and volatilisation losses. Humic microbial bio-stimulation could feasibly increase fertiliser efficiency and development of ecologically sustainable agriculture.
Over use of N fertilizers, most commonly as urea, had been seriously concerned as a major source of radiative N (Nr) for severe environment impacts through leaching, volatilization, and N2O emission from fertilized croplands. It had been well known that biochar could enhance N retention and use efficiency by crops in amended croplands. In this study, a granular biochar-mineral urea composite (Bio-MUC) was obtained by blending urea with green waste biochar supplemented with clay minerals of bentonite and sepiolite. This Bio-MUC material was firstly characterized by microscopic analyses with FTIR, SEM-EDS and STEM, subsequently tested for N leaching in water in column experiment and for N supply for maize in pot culture, compared to conventional urea fertilizer (UF). Microscopic analyses indicated binding of urea N to particle surfaces of biochar and clay minerals in the Bio-MUC composite. In the leaching experiment over 30 days, cumulative N release as NH4+-N and of dissolved organic carbon (DOC) was significantly smaller by >70% and by 8% from the BioMUC than from UF. In pot culture with maize growing for 50 days, total fresh shoot was enhanced by 14 % but fresh root by 25 % under Bio-MUC compared to UF. This study suggested that N in the Bio-MUC was shown slow releasing in water but maize growth promoting in soil, relative to conventional urea. Such effect could be related mainly to N retention by binding to biochar/mineral surfaces and partly by carbon bonds of urea to biochar in the Bio-MUC. Therefore, biochar from agro-wastes could be used for blending urea as combined organo/mineral urea to replace mineral urea so as to reduce N use and impacts on global Nr. Of course, how such biochar combined urea would impact N process in soil-plant systems deserve further field studies.
Biochar-based fertilizers have attracted increased attention, because biochar can improve the soil fertility, promote plant growth and crop yield. However, biochar-based controlled release nitrogen fertilizers (BCRNFs) still face problems because of the high cost, inefficient production technology, instability of nitrides, and the challenge associated with the controlled release of nutrients. In this study, we hydrothermally synthesised novel BCRNFs using urea-loaded biochar, bentonite and polyvinyl alcohol for controlled release of nutrients. Scanning electron microscopy and gas adsorption were conducted to identify the urea-loading and storage of bentonite in the inner pores of the biochar particles. X-ray diffraction, Fourier transform infrared spectroscopic and X-ray photoelectron spectroscopic studies demonstrated that strengthening the interactions among biochar, urea, and bentonite, helps control the moisture diffusion and penetration of bentonite, thereby leading to nutrient retention. The BCRNF showed significantly improved nutrient release characteristic compared with that of a mixture of biochar and urea. This urea-bentonite composite loaded with urea provides control over the release of nutrients stored in the biochar. BCRNF, especially those produced hydrothermally, can have potential applications in sustainable food security and green agriculture.
The application of most slow-release fertilizers is limited by complex preparation processes and short slow-release periods. In this study, carbon spheres (CSs) were prepared by a hydrothermal method using cellulose as the raw material. Using CSs as the fertilizer carrier, three new carbon-based slow-release nitrogen fertilizers were prepared using direct mixing (SRF-M), water-soluble immersion adsorption (SRFS), and co-pyrolysis (SRFP) methods, respectively. Examination of the CSs revealed regular and ordered surface morphology, enrichment of functional groups on the surfaces, and good thermal stability. Elemental analysis showed that SRF-M was rich in nitrogen (total nitrogen content of 19.66 %). Soil-leaching tests showed that the total cumulative nitrogen release of SRF-M and SRF-S was 55.78 % and 62.98 %, respectively, which greatly slowed down the release of nitrogen. Pot experiment results revealed that SRF-M significantly promoted the growth of pakchoi and improved crop quality. Thus, SRF-M was more effective in practical applications than the other two slow-release fertilizers. Mechanistic studies showed that CN, -COOR, pyridine-N and pyrrolic-N participated in nitrogen release. This study thus provides a simple, effective, and economical method for the preparation of slow-release fertilizers, providing new directions for further research and the develop of new slow-release fertilizers.
The livestock industry needs to use crop straws that are highly digestible to improve feed productivity and reduce ruminal methane emissions. Hence, this study aimed to use the ozonation and pelleting processes to enhance the digestibility and reduce the ruminal methane emissions of wheat straw enriched with two nitrogen sources (i.e., urea and heat-processed broiler litter). Various analyses were conducted on the pellets, including digestibility indicators, mechanical properties, surface chemistry functionalization, chemical-spectral-structural features, and energy requirements. For comparison, loose forms of the samples were also analyzed. The nitrogen-enriched ozonated wheat straw pellets had 43.06 % lower lignin, 28.30 % higher gas production for 24 h, 12.28 % higher metabolizable energy, 13.78 % higher in vitro organic matter digestibility for 24 h, and 28.81 % higher short-chain fatty acid content than the nitrogen-enriched loose sample. The reduction of methane emissions by rumen microorganisms of nitrogen-enriched wheat straw by ozonation, pelleting, and ozonation-pelleting totaled 89.15 %, 23.35 %, and 66.98 %, respectively. The ozonation process resulted in a 64 % increase in the particle density, a 5.5-time increase in the tensile strength, and a 75 % increase in the crushing energy of nitrogen-enriched wheat straw. In addition, ozone treatment could also reduce the specific and thermal energy consumption required in the pelleting process by 15.10 % and 7.61 %, respectively.
Utilization of kraft lignin to produce bio-based adsorptive material for effective dye adsorption from industrial wastewater is essential to fulfilling the significant environmental protection needs. Lignin is the most abundant byproduct material with a chemical structure containing various functional groups. However, the complicated chemical structure makes it somewhat hydrophobic and incompatible, which limits its direct application as an adsorption material. Chemical modification is a common way to enhance lignin properties. In this work, the kraft lignin was modified through direct amination using Mannich reaction and oxidization followed by amination as new route of lignin modification. The prepared lignins, including aminated lignin (AL), oxidized lignin (OL), and aminated-oxidized lignin (AOL), as well as unmodified kraft lignin, were analyzed by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), elemental analysis and 1H-nuclear magnetic resonance measurements (1HNMR). The adsorption behaviors of modified lignins for the malachite green in aqueous solution were investigated well and discussed, as well as the adsorption kinetics and thermodynamic equations. Compared with other aminated lignin (AL), the AOL displayed a high adsorption capacity of 99.1 % dye removal, due to its more effective functional groups. The change in structure and functional groups on the lignin molecules during oxidation and amination had no effect on its adsorption mechanisms. The adsorption process of malachite green on different kinds of lignin belongs to endothermic chemical adsorption, which mainly consists of monolayer adsorption. The modification of lignin through oxidation followed by amination process, afforded kraft lignin a broad potential application in the field of wastewater treatment.
The over-use of synthetic nitrogen (N) fertilisers for crop production can cause environmental pollution through leaching and gaseous losses, resulting in low N use efficiency (NUE). Previous work has shown that brown coal (BC) combined with urea can slow down the fertiliser-N release to better synchronise soil N supply with crop N demand. The study aimed to evaluate the impact of granulated BC-urea (BCU) applied to sweet corn on NUE, fate and recovery of fertiliser-N using an 15N tracer technique. In this in-field microcosm study, 10 atom percent enriched 15N-labelled urea (46% N) and BCU (20% N) were applied as N fertilisers at rates of 90 or 180 kg N ha-1. On average, BCU fertiliser reduced the urea-derived 15N losses as nitrous oxide (N2O) by 64%, ammonia (NH3) by 73% and downward movement of total N by 59% compared to urea. Reduced losses of applied BCU fertiliser-15N were associated with significantly increased microbial immobilisation, soil retention and availability of fertiliser-15N to plants for longer periods of time, compared with urea. As a result, BCU enhanced cob yield by an average of 23%, 15N uptake by 21% and fertiliser NUE by 21% over urea. The plant recovery of fertiliser-15N was significantly higher from BCU (59%) than the recovery from urea (38%). Moreover, mining of native soil-N was lower when the N-fertiliser source was BCU cf. urea, suggesting that BCU could be used as a more N-efficient alternative to urea in cropping systems.
Ammonium nitrogen (NH4+-N) is a form of N that is non-negligible in eutrophication water as well as an essential nutrient for plants growing. Carbon materials are considered superior for the adsorption recovery of excess NH4+-N in water bodies. The sulfonic-humic acid char (SHAC) was prepared from humic acid (HA) by pyrolysis and hydrothermal grafting with sodium allyl sulfonate. SEM-mapping, FTIR and XPS results indicated that sulfonic groups (-SO3H) were successfully grafted onto SHAC. The adsorption kinetic fitting displayed that the adsorption of NH4+-N by SHAC conformed to the pseudo-second-order kinetics and could reach equilibrium in about 100 min. The maximum adsorption of NH4+-N by SHAC was 77.24 mg/g, it was mainly contributed by electrostatic attraction, hydrogen bonding and pore volume sites. SHAC adsorption of NH4+-N resulted in the material SHAC-N, which desorption rate was considerably slower than that of commercially available ammonium chloride (NH4Cl) fertilizer and in accordance with the first order model. Wheat growth experiments revealed that the quality of wheat treated with SHAC-N (higher 100-grain weight and lower nitrate content) was better than that of NH4Cl fertilizer. In addition, the higher residual NH4+-N in the SHAC-N treatment soil facilitated subsequent crop planting. These results indicated that SHAC has excellent adsorption and slow release of NH4+-N, and has great potential application for N management in environment and agriculture.
The N losses and agronomic performances of newly developed slow-releasing fertilisers (SRFs; Epox5 and Poly5) were tested against conventional N fertilisers, urea and diammonium phosphate (DAP), in a climate-controlled lysimeter system. The dry matter (DM) yield and N losses of SRFs were not significantly different from urea and DAP. However, nitrate leaching and nitrous oxide (N2O) losses were unexpectedly low and therefore, it was inferred that nitrate underwent a chemical transformation. It was observed that a thick fibreglass wick interrupted drainage and created an anaerobic condition in the soil. The subsoil was found to have a high extractable total iron and it was postulated that iron played a role in the observed low level of N losses. An investigation was carried out with a factorial design using sand types and rates of N application as the main factors. Two types of sand; with high and low iron concentration and four levels of N applications; 0 (control), 50, 100 and 200 kg N ha−1 were employed in a leaching column and nitrate and N2O losses were measured. The nitrate leaching was significantly (P < 0.05) affected by sand types wherein a lower nitrate level was recorded for high‑iron concentration sand than for low-iron concentration sand at all N application levels. The N2O emission was significantly (P < 0.05) lower for high-iron sand than for low-iron sand for the 200 N treatment, but not significantly different between sand types for other treatments. These observations provide evidence for the involvement of iron in nitrate transformation under anaerobic conditions and it was hypothesised path was dissimilar nitrate reduction (DNR). Further studies are recommended, to identify the underlying mechanism responsible for nitrate reduction with iron-rich sand.
A cost-effective and energy-efficient nitro-humification process (urea pretreatment and ozone plasma oxidation) was developed for nitrogen functionalization and activation of the humic substances (HSs) of lignite. Different nitro-humification metrics, i.e., solubility, physicochemical properties, oxidation degree, nitrogen functionalization, spectral ratios, and surface functionalization, along with energy efficiency and economic profitability, were determined for the processed lignite. The best solubility metrics for the lignite were obtained under 3 wt% ozone, 10 wt% KOH, and 20 wt% urea. The selected conditions could increase alkali- and water-soluble HSs by 2.25 and 2.94 times, respectively, compared with the conventional alkaline extraction method. The process could result in a balanced distribution between nitrogen binding forms. The functionalized lignite showed a 14.5% reduction in the carbon content due to ozone oxidation and an 8.15% nitrogen enrichment due to urea pretreatment, leading to an ideal C/N ratio (5.6%) and a higher O/C ratio (0.94). The humification index (E4/E6 ratio of 6.8) and salt index (46.21%) were acceptable. The process could increase the cation exchange capacity of the lignite by 3.83 times while enhancing its carboxylic and phenolic groups by 215.87% and 85.71%, respectively. The crystallinity index of the processed lignite was increased by 2 times, and the availability of its macro-micronutrients and rare earth elements was increased by 6.35 times and 43.38%, respectively. The nitro-humic products showed lower heavy metals with higher micropores-mesopores in a globular-like and heterogeneous porous structure. The proposed method could increase the process energy efficiency by 59.91% while discounting the production costs by 43%.
The contradiction between population growth and soil degradation has been increasingly prominent, such that novel fertilizers (e.g., biochar and microbial fertilizers) should be urgently developed. Biochar is a promising fertilizer carrier for microbial fertilizers due to its porous structure. However, the preparation and mechanisms of the effects of biochar-based microbial fertilizers have been rarely investigated. In this study, biochar, Bacillus, and exogenous N-P-K fertilizers served as the raw materials to prepare biochar-based microbial fertilizers (BCMFs) by optimizing the preparation methods and the process parameters. Moreover, the release patterns of N-P-K were analyzed. A pot experiment was performed on pakchoi to examine the effect of the BCMFs and explore its synergistic effect on soil fertility. The results of this study indicated that adsorption by biochar maintained bacterial activity, whereas the granulation process reduced bacterial activity. The adsorption-granulation process increased the content of total nitrogen and organic matter in the soil while enhancing the slow-release effect of the BCMFs. The Elovich model was capable of describing the nitrogen release of the BCMFs, including the diffusion and chemical processes. As indicated by the result of the column leaching experiment, the BCMFs stopped nutrient leaching more significantly than the conventional fertilizers (CF), especially in stopping N and P leaching. The use of the BCMFs improved the available soil nutrients and soil quality while enhancing the abundance of bacteria correlated with carbon and nitrogen metabolism in the soil. Moreover, a 20 % reduction in the use of the BCMFs did not significantly affect the soil available N and P and the growth status of pakchoi. The result of redundancy analysis indicated that the cation exchange capacity (CEC), NH4⁺-N, NO3⁻-N, β-glucosidase (BG), urease (URE), and alkaline phosphatase (AlkP) were the six critical environmental factors for the microbial community structure and could explain 94.8 % of the variance. The BCMFs up-regulated the levels of the above six factors, especially CEC and BG, thus improving the soil quality and enhancing the soil fertility.
Biochar is a product of the thermal treatment of biomass, and it can be used for enhancing soil health and productivity, soil carbon sequestration, absorbance of pollutants from water and soil, and promoting environmental sustainability. Extensive research has been done on applications of biochar to enhance the Water Holding Capacity (WHC) of biochar amended soil. However, a comprehensive road map of biochar optimised for enhanced WHC, and reduced hydrophobicity is not yet published. This review is the first to provide not only quantitative information on the impacts of biochar properties in WHC and hydrophobicity, but also a road map to optimise biochar for enhanced WHC when applied as a soil amendment. The review shows that straw or grass-derived biochar (at 500–600 °C) increases the WHC of soil if applied at 1 to 3 % in the soil. It is clear from the review that soil of varying texture requires different particle sizes of biochar to enhance the WHC and reduce hydrophobicity. Furthermore, the review concludes that ageing biochar for at least a year with enhanced oxidation is recommended for improving the WHC and reducing hydrophobicity compared to using biochar immediately after production. Additionally, while producing biochar a residence time of 1 to 2 h is recommended to reduce the biochar's hydrophobicity. Finally, a road map for optimising biochar is presented as a schematic that can be a resource for making decisions during biochar production for soil amendment.
Due to the population growth, there is an urgent need for sustainable technologies and products to address the imbalance between the availability of arable land and growing food needs. Increasing crop productivity in a cost-efficient and environmentally-friendly pathway is one approach to address this issue. In this study, lignin, a low-cost and underutilized biomass by-product of the pulping industry, was converted to a fertilizer via oxidation in the presence of KOH. The oxidation of lignin in water (15 wt.%) under the conditions of 195 °C temperature, 300 psi pressure, and KOH dosage of 30 wt.% (based on dried lignin) generated water-soluble lignin enriched with carboxylate groups. The X-ray photoelectron spectroscopy (XPS) and proton nuclear magnetic resonance (¹H NMR) analyses confirmed the introduction of carboxylate groups to lignin, while ³¹P NMR and heteronuclear single quantum coherence (HSQC) NMR studies confirmed the alterations in the aliphatic and aromatic structures of lignin. The fertilizing effects of oxidized lignin were investigated on Zea mays (maize) plants. The results confirmed that the average length and dry weight of the plants grown in the presence of oxidized kraft lignin were 27% and 92% greater than those produced without lignin, and they were 12% and 81% higher than those grown in the presence of humic acid, respectively. After 30 days, the plants grown in the presence of oxidized kraft lignin contained 14% and 32% more chlorophyll than those generated in the presence of humic acid and control samples, respectively. Finally, the ash content analysis of the plants shows that applying oxidized kraft lignin as a fertilizer can reduce the ash content and increase the organic content of plants. These results confirmed that the oxidation of kraft lignin in the presence of KOH could be a strategy to induce a green fertilizer for crop cultivation.
Increasing global demand for food production, often exasperated by excessive use of chemical fertilizers, has led to deterioration of soil health. Immediate action is needed to restore soil health in a sustainable manner. This review advocates switching to use of more organic matter (manure and compost) that contain vital nutrients for plant growth and help restore soil health. One important source of organic matter found ubiquitously in nature is humic substances, which are derived from degraded plant remains and their application to soil enhances essential nutrient supply and assimilation of atmospheric carbon dioxide (CO2) due to increased biomass yield. Promoting this globally can then lower atmospheric concentrations of carbon dioxide and create a sustainable agricultural practice. However, the process of humification and molecular structure of HSs remains a little understood subject of soil science. Therefore, it is imperative to understand the mechanism of various roles of HSs in agroecosystems. This review offers an insight into the various structural and functional aspects of HSs, particularly the humic acids (HAs). The dynamic and interactive nature of HSs creates the framework of sustainable agriculture.
Ozone is a powerful oxidative gas widely used as a green pretreatment to enhance the delignification of cereal straws. Urea pretreatment can enrich straws with nitrogen to make them more accessible to anaerobic microorganisms. This study aimed to evaluate the effect of ozone-urea pretreatment on the digestibility of wheat straw (i.e., physicochemical, nitrogen enrichment, gas production, nutritional value, and surface chemistry). The results of ozone-urea pretreatment were compared with non-pretreated, ozone-pretreated, and urea-pretreated samples. This pretreatment method outperformed the other methods in terms of digestibility metrics. The ozone-urea pretreatment resulted in a 50% reduction in lignin, a 4.2 times increase in crude protein, a 22.5% increase in bonded organic-N, a 2 times increase in 24 h-gas production, and a 43.67% increase in total digestible nutrients compared to the non-pretreated sample. Based on the total digestible nutrients index, one-tonne ozone-urea-pretreated straw would be 70.6 USD cheaper than the non-pretreated one.
Descending the application of nitrogen (N) fertilizers and promoting N utilization efficiency (NUE) are the keys to alleviating environmental pollution and achieving sustainable agricultural development. Humic acid urea (HU) as a novel slow-release urea fertilizer is beneficial for the enhancement of crop nitrogenous utilization rate. However, the effect of HU on the plant growth of maize supplied with reduced N fertilizer is still unclear. In the study, pot experiments were conducted to detect the impact of N fertilizer (urea) reduction combined with HU on the physiological characteristics and grain production of maize. The results revealed that an N fertilizer reduction caused serious N deficiency, which significantly decreased the total N in all plant tissues (leaves, stems, spikes, and roots), reduced SPAD values, and suppressed the efficiency of photosynthesis, resulting in remarkable decreases in dry weight, grain yield and NUE of maize. The application of HU alleviated the negative effect of N deficiency and significantly increased the plant total N content by 20.1–28.4%, SPAD values by 5.0–24.3%, leaf photosynthetic efficiency by 10.2–37.0%, and NUE by 41.7–77.5%, respectively. At the same N application rate, HU also increased the biomass and grain yield of maize by 30.2–59.1% and 12.6–39.1%, respectively. Furthermore, the HU application with a 15% reduction in the N application rate maintained the grain production of maize with no significant reduction. Collectively, our study indicated that HU could enhance the utilization rate of urea, promote N absorption and accumulation by plants, increase biomass, and consequently, increase the crop yield of maize.
Phosphorus (P) is an essential nutrient widely used in crops. Phosphate fertilizers are easily adsorbed on the soil surface, resulting in poor migration to the roots of crops, and a large amount of nutrients cannot be absorbed and utilized, resulting in waste of resources and low bioavailability. To solve the problem of insufficient mobility of phosphate fertilizer, this work uses TiO2-WO3 to catalyze the oxidation and pyrolysis of lignite to synthesize small molecular humic acid, and uses small molecular humic acid to coat commercial phosphate fertilizer (MAP) to obtain a new type of phosphate fertilizer (AMAP) with good fluidity. Water contact angle was determined from initially hydrophobic (132°) to hydrophilic (76°). Humic spectroscopic ratio (E4/E6), H/C and molecular weight distributions confirmed the effectiveness of the TiO2-WO3 catalyst and the successful modification of weathered lignite. The migration characteristics of phosphorus in the soil were studied by leaching migration experiments. The results showed that the effective phosphorus content of the new coated phosphate fertilizer (AMAP) in the soil exceeded that of the commercial phosphate fertilizer (MAP) at different vertical migration distances. After 21 d of incubation at the same fertilizer level, new coated phosphate fertilizer (AMAP) of phosphate fertilizer added with different products showed elevated levels of P. Migration data indicated that the migration distance of effective phosphorus approximated the long root distance of early corn, which benefitted crop growth. The pot experiment confirmed improved corn growth and improvement in the utilization rate of phosphorus fertilizer. All in all, activated lignite (AHA) can reduce or inhibit the fixation of phosphorus nutrients in the soil, and has obvious application value for improving the efficiency of phosphate fertilizers.
The adsorption behavior of the anionic dyes Remazol Brilliant Blue R (RBBR) and Reactive Black 5 (RB5) from aqueous solutions by polyethylenimine ozone oxidized hydrochar (PEI-OzHC) was investigated. The adsorption capacities of both dyes increased with functionalization of PEI in the hydrochar adsorbent. The results of surface characterization (FTIR, BET, TGA, elemental analysis, and SEM) showed that PEI modification greatly enhanced the adsorbent surface chemistry with a slight improvement of adsorbent textural properties. In addition, the adsorption kinetics data showed an excellent adsorption efficiency as reflected in the high removal percentages of the anionic dyes. The Isotherm results indicated that RBBR and RB5 dye adsorption occurred via monolayer adsorption, and chemisorption was the rate-controlling step. The PEI-OzHC adsorbent possesses higher maximum Langmuir adsorption capacity towards RBBR (218.3 mg/g) than RB5 (182.7 mg/g). This increase in adsorption capacity is attributed to the higher number of functional groups in RBBR that interact with the adsorbent. This study reveals the potential use of adsorbents derived from pine wood hydrochar in municipal as well as industrial wastewater treatment. Furthermore, surface chemistry modification is proven as an effective strategy to enhance the performance of biomass-derived adsorbents.
Nitrogen, the vital primary plant growth nutrient at deficit soil conditions, drastically affects the growth and yield of a crop. Over the years, excess use of inorganic nitrogenous fertilizers resulted in pollution, eutrophication and thereby demanding the reduction in the use of chemical fertilizers. Being a C4 plant with fibrous root system and high NUE, maize can be deployed to be the best candidate for better N uptake and utilization in nitrogen deficient soils. The maize germplasm sources has enormous genetic variation for better nitrogen uptake contributing traits. Adoption of single cross maize hybrids as well as inherent property of high NUE has helped maize cultivars to achieve the highest growth rate among the cereals during last decade. Further, considering the high cost of nitrogenous fertilizers, adverse effects on soil health and environmental impact, maize improvement demands better utilization of existing genetic variation for NUE via introgression of novel allelic combinations in existing cultivars. Marker assisted breeding efforts need to be supplemented with introgression of genes/QTLs related to NUE in ruling varieties and thereby enhancing the overall productivity of maize in a sustainable manner. To achieve this, we need mapped genes and network of interacting genes and proteins to be elucidated. Identified genes may be used in screening ideal maize genotypes in terms of better physiological functionality exhibiting high NUE. Future genome editing may help in developing lines with increased productivity under low N conditions in an environment of optimum agronomic practices.
Supplementary information:
The online version contains supplementary material available at 10.1007/s12298-021-01113-z.
Effective fertilizer nitrogen (N) management plays an important role in reducing the environmental problems caused by its overuse in maize production systems. The use of enhanced-efficiency N fertilizers is an effective approach to increase crop productivity and N use efficiency. However, to the best of our knowledge, there have been no associated comprehensive evaluations of the environmental impacts using a life cycle assessment (LCA) and ecosystem economic benefits (EEB). In this study, a consecutive 2-yr plot-based field experiment was conducted in Southwest China with two N fertilizer sources, blended urea (BU) containing controlled-release urea and conventional urea (CU) at a 1:1 ratio and CU only at five N rates (0, 90, 180, 270, and 360 kg N ha⁻¹) to determine the agronomic and environmental benefits as well as the EEB of BU in maize production. The results showed that among the five N rates tested, the N180 treatment (180 kg N ha⁻¹) showed greater potential for maintaining a high yield (8.8 Mg ha⁻¹) and reducing environmental impacts. The use of BU resulted in higher grain yield and agronomic efficiency compared to those with CU at 180 kg N ha⁻¹ in 2018 but not in the following year. In addition, BU significantly reduced reactive nitrogen losses through nitrous oxide emission (−27%), ammonia volatilization (−18%), and N leaching (−24%), reducing the crop environmental footprint by decreasing the global warming, acidification, and eutrophication potential by 8%–13%, 4%–9%, and 8%–22%, respectively. Furthermore, the use of BU increased economic benefits and EEB by reducing agricultural (N fertilizer; labour) and ecological costs. Compared to CU, BU improved the EEB by 68%, 39%, 29%, and 25% at N rates of 90, 180, 270, and 360 kg N ha⁻¹, respectively. These results demonstrated that replacement of CU with BU at the N rate of 180 kg N ha⁻¹ is an effective strategy to improve sustainability of maize production in subtropical regions of China.
The use of agro-biowaste compost fertilizers in agriculture is beneficial from technical, financial, and environmental perspectives. Nevertheless, the physical, mechanical, and agronomical attributes of agro-biowaste compost fertilizers should be engineered to reduce their storage, handling, and utilization costs and environmental impacts. Pelletizing and drying are promising techniques to achieve these goals. In the present work, the effects of process parameters, including compost particle size/moisture content, pelletizing compression ratio, and drying air temperature/velocity, were investigated on the density, specific crushing energy, and moisture diffusion of agro-biowaste compost pellet. The Taguchi technique was applied to understand the effects of independent parameters on the output responses, while the optimal pellet properties were found using the iterative thresholding method. The soil and plant (sweet basil) response to the optimal biocompost pellet was experimentally evaluated. The farm application of the optimal pellet was also compared with the untreated agro-biowaste compost using the life cycle assessment approach to investigate the potential environmental impact mitigation of the pelletizing and drying processes. Generally, the compost moisture content was the most influential factor on the density and specific crushing energy of the dried pellet, while the moisture diffusion of the wet pellet during the drying process was significantly influenced by the pelletizing compression ratio. The density, specific crushing energy, and moisture diffusion of agro-biowaste compost pellet at the optimal conditions were 1242.49 kg/m³, 0.5054 MJ/t, and 8.2×10⁻⁸ m²/s, respectively. The optimal biocompost pellet could release 80% of its nitrogen content evenly over 98 days, while this value was 28 days for the chemical urea fertilizer. Besides, the optimal pellet could significantly improve the agronomical attributes of the sweet basil plant compared with the untreated biocompost. The applied strategy could collectively mitigate the weighted environmental impact of farm application of the agro-biowaste compost by more than 63%. This reduction could be attributed to the fact that the pelletizing-drying processes could avoid methane emissions from the untreated agro-biowaste compost during the farm application. Overall, pelletizing-drying of the agro-biowaste compost could be regarded as a promising strategy to improve the environmental and agronomical performance of farm application of organic biofertilizers.
In modern agriculture, fertilizers are the most significant prerequisite to ensure sustainable crop production, and the intervention of chemical fertilizers has markedly increased crop production and quality. Unfortunately, plants cannot uptake a significant amount of nutrients (>50%) from the applied fertilizers, resulting in low fertilizer use efficiency. The nutrient losses due to leaching, volatilization, denitrification, fixation, erosion, and runoff could result in low fertilizer use efficiency and create environmental pollution as well as a rise in the cost of fertilizer application. To minimize such losses, researchers have suggested various strategies, one of which is the synthesis and application of slow-release fertilizers to extend the bioavailability of nutrients by the sustained release throughout the crop growth period. However, the high cost of current slow-release fertilizers is a major challenge for their widespread use. Carbon-based materials, especially biochar and lignite, have been shown to be effective as soil amendment in recent times. Additionally, these materials have an excellent ability to adsorb nutrients due to their high porosity, surface area, and abundance of functional groups. The cost-effective and abundant supply of these materials across the world can serve as an excellent nutrient-carrier in order to formulate climate-smart and cost-effective slow-release fertilizers. In this review paper, the potential of these materials as nutrient carriers, nutrient adsorption and desorption mechanisms, synthesis methods, nutrient release behavior, and agronomic and environmental implications are discussed in detail for future research priorities as the literature in this direction is very limited and scattered.
The present work investigates the optimization of humic acids (HAs) production from lignite processing wastes using a developed mechanical agitated (MA) tank reactor based on results of response surface methodology (RSM). The structures of the obtained HAs were characterized using elemental analysis, spectroscopy, scanning electron microscopy (SEM), particle size distribution (PSD), acidic functional groups, and ash content. The highest extraction efficiency of HA was 54.2%, which was obtained from the MA tank reactor under optimal conditions of using 0.5 M NaOH, the reaction time of 4 h, stirring speed of 850 rpm, and temperature of 70 °C. The developed MA tank reactor was capable of improving the HA extraction and energy efficiency of the process up to 26.9% and 24.8%, respectively, compared to the conventional magnetic stirred (MS) glass reactor. The extracted HA from the MA tank reactor exerted better quality indices, including higher oxygen content (37.02%), higher C/N and O/C ratios (61.26 and 0.47, respectively), higher total acidity and phenolic-OH contents (8.87 and 5.6 meq.g⁻¹, respectively), higher E4/E6 ratio (3.765), more homogeneously porous structure, higher specific surface area, lower H/C ratio (0.64), and lower ash content (2.2%), than the MS method, which indicate its suitability in agricultural applications.
To improve fertilizer use efficiency, reduce irrigation requirement, and minimize negative environmental impact, a novel large-grained-activated-lignite-slow-release fertilizer (LAF) with good water retention was developed by mechanical extrusion of activated lignite and traditional fertilizer. A 3D molybdate-sulfur hierarchical hollow nanosphere (3D-MoS2-HN) catalyst was successfully fabricated via a simple route and the lignite was activated by 3D-MoS2-HN to increase its water-soluble humic acid content and nutrient adsorption ability. After activation, the amounts of small molecular active groups and water-soluble humic acid of activated lignite was significantly higher than those of raw lignite. The activation also increased adsorption ability of the activated lignite for nutrients. LAF prepared from the activated lignite had preferable slow-release property and good water-holding capacity in soil. Moreover, a pot trial further demonstrated that LAF effectively improved the growth of apple plant. With outstanding water-retention and slow-release capacities, this new fertilizer is economical and eco-friendly, and thus is promising in field applications.