Soil Amendment Research Articles

Biochar & fly ash amendments lower mortality and increase antioxidant activity in chlorpyrifos-exposed earthworms

The investigation presented a novel finding regarding mitigating stress induced by chlorpyrifos in Eisenia fetida by incorporating biochar derived from rice straw and fly ash as soil amendments. It was observed that phenolic compounds exhibit solubility in methanol, and the methanolic fraction exhibited notable inhibitory effects on lipid peroxidation and displayed antioxidant properties. The defence mechanism of E. fetida, comprising catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and various other enzymes, remained effective in neutralizing stressors without disruption when the earthworm was subjected to diverse chemical agents or stressful conditions. These enzymes served as indicative markers of toxicity induced by pesticide exposure, even at sublethal concentrations. The scavenging of free radicals by these enzymes ultimately safeguarded the organism. Fly ash and biochar emerged as two organic alternatives capable of alleviating stress by providing a protective mechanism. In this context, the study examined the impact of biochar and fly ash amendments on earthworm biomarkers. The mortality rate at the median lethal concentration of chlorpyrifos was reduced to less than 50% through 3% and 5% modifications. In contrast to the non-amendment group exposed to sublethal doses, the amendment group exhibited higher levels of oxidative stress and lower protein content. This observation indicated the presence of stress induced by the accumulation of free radicals, which increased in number with higher doses of chlorpyrifos. Moreover, the study highlighted the interconnected nature of total antioxidant capacity and total phenolic capacity values, with a decrease in these parameters signifying a shift in earthworm biomarkers.Graphical abstract

Soil application of activated hydrochar derived from sewage sludge enhances plant growth and reduces nitrogen loss

Sewage sludge treatment and disposal is a considerable environmental and economic burden, and is considered a major global challenge. Here, sewage sludge treatment and disposal were studied with a focus on hydrothermal carbonization and the use of hydrochar (HC) as a soil amendment after Fenton-reaction activation. The underlying hypothesis was that enhanced adsorption of nutrients (e.g., ammonium) by activated HC (AHC) increases their availability, thus enhancing plant growth and reducing environmental impacts such as greenhouse gas emission and N leaching relative to conventional soil-amendment techniques.The impact of AHC on lettuce plant growth, N leaching, ammonia volatilization, soil trace-gas emissions, and respiration was studied in a net-house planting experiment. Four treatments were tested in quadruplicate using sandy loam soil with addition of either AHC, urea fertilizer, or AHC plus urea, and a control with no amendment.Activation-induced changes in AHC surface properties (indicated by SEM and XPS analyses) resulted in an NH4+ adsorption capacity 60 % higher than that of untreated HC. The AHC + urea soil treatment yielded the most enhanced plant growth, followed by urea and AHC treatments with comparable growth rates. Least growth occurred in the control with no amendment. Nitrogen loss through gas emissions, per kg of lettuce, was lowest with AHC + urea treatment, although its mean N emission as nitrous oxide (N2O) was notably higher at 2.3 mg N2O-N kg−1 than for other treatments (∼0.4 mg N2O-N kg−1). Dissolved-N leaching was reduced by up to four times with AHC treatment due to its higher NH4+ adsorption capacity, indicating reduced environmental impact of the AHC amendment.AHC application is therefore considered a sustainable soil amendment, enhancing plant growth and reducing N loss and sewage environmental impact.

Amended soils with weathered coal exhibited greater resistance to aggregate breakdown than those with biochar: From the viewpoint of soil internal forces

Soil erosion is the first threat to soil functions. Reducing the soil aggregate breakdown strength is a key step to improve the soil’s ability to resist rainfall splash erosion. Soil internal forces have been found to be the initial and important forces driving aggregate turnover. The application of exogenous organic materials can effectively improve soil aggregate stability and the resistance to rainfall erosion of agricultural soils. However, from the perspective of soil internal forces, information about the reduction effects of the exogenous organic materials application on soil aggregate breakdown is scarce, especially in comparing the effects of different materials. In this study, weathered coal and biochar were individually applied to loamy clay soil at rates of 0 %, 1 %, 2 %, and 3 % (w/w). Soil internal forces, aggregate breakdown strength, and splash erosion rate of different amended soils were then examined after four years. The results showed that compared with unamended soils (0 %), both weathered coal and biochar applications clearly increased the van der Waals attractive pressure and thus decreased the positive net pressure between soil particles. Additionally, these materials reduced soil aggregate breakdown strength and splash erosion rate. The application effects of the two materials were increased with their application rates. Under a lower electrolyte concentration in soil solution (0.0001 mol L−1), the aggregate breakdown strength in the soils amended with weathered coal was lower than that with biochar by 9.6 %, 23.2 %, and 17.7 % (when the diameter of broken aggregate was < 10 μm) and by 10.3 %, 20.8 %, and 17.5 % (when the diameter of broken aggregate was < 20 μm) at the 1 %, 2 %, and 3 % application rates, respectively (P < 0.05). Additionally, soils amended with weathered coal exhibited lower splash erosion rates compared to those amended with biochar, particularly at the higher application rate of 3 %. From the viewpoint of soil internal forces, weathered coal appears to be a suitable exogenous organic material for improving soil aggregate stability and anti-erosion ability during rainfall events. Our findings provide valuable insights into utilizing exogenous materials to improve soil resistance to rainfall splash erosion, assisting agricultural soil management in areas frequently affected by rainfall erosion.

Soil amendment mitigates mortality from drought and heat waves in dryland tree juveniles

Soil amendment mitigates mortality from drought and heat waves in dryland tree juveniles

Prospects of torrefied biomass as soil amendment for sustainable agriculture

Prospects of torrefied biomass as soil amendment for sustainable agriculture

Systematic review assessing the effects of amendments on acidic soils pH in tea plantations.

Soil acidification has emerged as a critical limiting factor for the sustainable development of the tea industry. In this article, a comprehensive review of 63 original research articles focusing on the impact of amendments on the pH in tea plantations soil was conducted. Through meta-analysis, the effect of applying soil amendments to increase the pH of tea plantation soil and its influencing factors were investigated. The results revealed that lime had a significant impact, increasing the pH by 18% in tea plantation soil, while rapeseed cake had a minimal (2%) effect. It was observed that as the quantity of amendments and pH levels increased, so did their impact on the pH of tea plantation soil. Subgroup analysis within biochar showed varying effects, depending on soil pH, with an 11% increase in acidic soil. Among these amendments, biochar produced at pyrolysis temperature ranging from 501-600 °C and derived from animal waste demonstrated significant effect on increasing soil pH in tea plantations by 9% and 12%, respectively. This study offers valuable insights into improving and ensuring the health and sustainability of tea plantations.

Bamboo charcoal application altered the mineralization process of soil organic carbon in different succession stages of karst forest land

Introduction: As a soil amendment, Bamboo charcoal helps to contributes to the improvement of soil carbon sequestration, but its effect on the accumulation and transformation of different soil organic carbon in soil of karst forests is not clear.Methods: The research focused on three distinct forest land succession stages: virgin forest, secondary forest, and planted forest. A 60-day indoor constant temperature culture experiment was conducted, applying bamboo charcoal to the soil of the three forest lands at four different addition ratios: 0%, 1.0%, 2.0%, and 4.0%. The analysis aimed to study the characteristics of SOC mineralization, different carbon fractions of organic carbon, and soil enzyme activity.Results: The findings revealed that bamboo charcoal application led to an increase in the organic carbon (SOC) content within the three forest soils. Moreover, the organic carbon content showed an increase corresponding to the increased proportion of bamboo charcoal, with the highest SOC content observed in the planted forest land with 4.0% bamboo charcoal. The overall performance of the C0/SOC value in the three forest soils was ranked as follows: planted forest &amp;lt; secondary forest &amp;lt; virgin forest (C0: the mineralization potential of soil organic carbon). In both planted and secondary forest soils, the C0/SOC value increased after the application of bamboo charcoal. However, in the virgin forest soil, the application of 1.0% and 4.0% bamboo charcoal reduced the C0/SOC value, while the application of 2.0% bamboo charcoal increased the C0/SOC value. Particularly the C0/SOC value of the planted forest soil without bamboo charcoal was the smallest at 0.047, whereas that in the virgin forest soil with 2.0% bamboo charcoal had the largest value at 0.161.Discussion: Herein, appropriate human intervention can enhance the carbon sequestration potential of forest soil, in different succession stages within the karst area. However, the external application of bamboo charcoal does not significantly improve the carbon sequestration potential in the planted and secondary forest. Notably, applying a higher proportion (4.0%) of bamboo charcoal can enhance the organic carbon sequestration potential, particularly in the virgin forest soil, representing the climax community of forest succession.

Improving biochar properties through liquid-phase exfoliation of onion peel biochar doped with chicken feathers

In recent decades, heightened environmental awareness has spurred a global push for innovative waste-to-wealth solutions. This study explores liquid-phase exfoliation as a strategy to enhance biochar properties. By doping onion peels and chicken feathers, hybrid biochar (HBC) was produced using a low-temperature co-carbonization system. Two exfoliation routes, the nitric acid and acetone routes, were compared with the un-exfoliated HBC through material characterization. Material characterization revealed distinct morphological features and a range of functional groups being introduced by exfoliation. It was also observed through the BET analysis that the HBC samples are mesoporous, with the exfoliated HBCs having an enhanced surface area and pore volume. Elemental analysis showcased HBC's fortification, highlighting potential applications such as adsorbents and soil amendments. This investigation shows the efficacy of liquid-phase exfoliation in enhancing biochar surface characteristics, opening avenues for diverse applications.

Ironstone and red mud barriers to reduce subsurface movement of soil phosphorus.

Loss of phosphorus in seepage may contribute to eutrophication of downstream water bodies. This study examined the potential use of pedogenic ironstone and untreated red mud (bauxite refining residue) as P sorbents in a permeable reactive barrier (PRB) to mitigate such loss. Effects of ironstone and red mud on P sorption (batch), transport (columns), saturated hydraulic conductivity (KS), and growth of common bermudagrass (Cynodon dactylon; greenhouse) were examined. Both materials had sorption maxima of ∼30mmol Pkg-1 or about five times that of a P-enriched sandy soil; however, sorption by red mud greatly increased with decreasing pH. Transport of P through columns of ironstone and red mud (diluted with nonreactive sand) was similar and slower compared to soil+sand. However, when red mud was mixed with soil, increased sorption at lower pH resulted in greater P retention compared to ironstone+soil (76%vs. 13%). Although addition of ironstone to soil up to 20% did not reduce KS, red mud at even 5% did. Soil amendment with red mud increased bermudagrass growth and P uptake. Given long-term neutralization of red mud in an acidic soil and increased P sorption, it may be suitable in a PRB if incorporated at a low rate and/or co-incorporated with a coarser material.

Synergistic impact of Rhizobium and arbuscular mycorrhizal fungi on lentil plant tolerance to heavy metal-rich fly ash amended soil

The purpose of the study was to investigate the impact of microbes [symbiotic bacteria viz. Rhizobium (Frank) and the arbuscular mycorrhizal fungi (AMF) viz. Funneliformis caledonius (Nicolson & Gerd.) and Glomus bagyarajii Mehrotra] on the growth and physiology of lentil (Lens culinaris Medik.) cultivated in soil alone and soil amended with fly ash. The experiment had twenty-four treatments, twelve in sterilized soil and twelve in unsterilized soil (with six treatments in soil alone and six in soil amended with fly ash in both the sets). Amendment of soil with 25% fly ash significantly increased plant growth. Microbial inoculation further increased the plant growth and physiological parameters studied (plant length, fresh and dry weight, chlorophyll and protein content, and nitrate reductase activity). Microbial parameters like nodule number and fresh weight, mycorrhizal root colonization and spore numbers were also significantly higher in plants inoculated with Rhizobium + AMF. Soil amendment with 25% fly ash together with inoculation of Rhizobium + AMF further improved the growth of lentil. Plant heavy metal (Cd, Pb, Zn) content was significantly more in soil amended with fly ash, but microbial inoculation significantly decreased heavy metal uptake. Of the two AM fungus studied F. caledonius proved to be better, resulting in higher plant growth and physiological parameters studied with reduced heavy metal uptake.

Açaí Seed Biochar-Based Phosphate Fertilizers for Improving Soil Fertility and Mitigating Arsenic-Related Impacts from Gold Mining Tailings: Synthesis, Characterization, and Lettuce Growth Assessment

Biochar represents a promising alternative for enhancing substrates and remediating contaminants in mining areas. Given that arsenic (As) and phosphorus (P) share similar chemical forms, the combination of biochar and P fertilizers may reduce As uptake, thereby mitigating As-related impacts. This study aimed to evaluate the potential of biochar-based P fertilizers in improving soil fertility and mitigating human health risks from gold mining tailings in the eastern Brazilian Amazon. Biochar from açaí palm (Euterpe oleracea Mart.) seeds was produced through enrichment with single and triple superphosphate at a ratio of 1:4, at 400 °C, and applied to mining tailings at 0.5%, 1%, and 2%. After one year of incubation, lettuce plants were grown for 70 days. Biochar reduced As absorption by lettuce and improved biomass and nutrient accumulation, resulting in improved vegetation indices. Biochar was effective in reducing non-carcinogenic As risks via ingestion of soil and plants to acceptable levels. Regression equations explained the As absorption behavior as affected by the biochar and the importance of biochar-related nutrients in reducing As stress. This study demonstrates the potential of P-enriched biochar as an amendment for As-contaminated soils, reducing As absorption, increasing P availability, and improving plant growth.

Stabilization of lead (Pb)- and arsenic (As)-contaminated soil using pen shells (Atrina pectinata).

Pen shells (PS), a type of shellfish, are abundantly consumed, and their inedible shell residues are often discarded near the coast without consideration of reutilization. This study sought to investigate the use of natural pen shells (NPS) and calcined pen shells (CPS) to stabilize Pb and As-contaminated soil. During the investigation, NPS and CPS were applied to the contaminated soil in amounts ranging from 1 to 10 wt% and cured for 28days. After the curing process, the mineral phase was examined through X-ray powder diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis. The XRD and SEM-EDX results revealed the presence of riversideite and ettringite, which contribute to Pb and As stabilization in the CPS-treated soil. The leachability of Pb and As in the treated soil was further examined with three types of chemical extraction methods. Extraction results using 0.1M HCl displayed a notable pH fluctuation in the extractant due to the residual amendments (NPS and CPS). The fluctuation resulted in a strong correlation of leached Pb and As with the pH of the extractant, which might hinder an accurate assessment of stabilization. In order to minimize the effect of pH, an EDTA-NH4OAc extraction was employed, suggesting its potential as a suitable assessment method. EDTA-NH4OAc extraction showed a higher effectiveness of CPS than NPS at 10 wt% of input amounts. In the SBET extraction, that uses a strongly acidic solution, a higher As leachability was observed by increasing the addition of CPS, which implied a CPS-related chemical fixation mechanism. The comparison of various extraction methods showed a higher CPS effectiveness as compared to NPS. However, it was recommended that CPS-treated soil required caution in strongly acidic conditions, especially for arsenic. This study explores the applicability of PS, which has not been investigated as an amendment for Pb and As-contaminated soil previously. Furthermore, this study revealed that utilization of various extraction methods is beneficial for gaining a comprehensive understanding of the role of CaCO3-based amendment in Pb and As-contaminated soil.

Determination of persistent organic pollutants in urban and peri-urban wastewater sludge: environmental and carcinogenic human risk assessment in the case of land application.

The management of digested sludge derived from treatment water plants is a problem worldwide due to the possible transfer of contamination from sludge to amended soil and, in turn, to humans. Within this work, through a chemometric experimental design, a robust GC-MS method for the simultaneous determination of two classes of micropollutants of concern (polycyclic aromatic hydrocarbons-PAHs-and polychlorinated biphenyls-PCBs-including dioxin-like compounds) was developed using microwave-assisted extraction (MAE). The method, which showed interesting greenness features in compliance with the 12 principles of Green Chemistry, allowed PCB and PAH extraction with recoveries higher than 75% (RSD < 14%) with method detection limits between 4.6 and 11.5µgkg-1 (PAHs) and between 6.9 and 13.7µgkg-1 (PCBs), without preconcentration. The matrix effect was below 20%. The validated protocol allowed the characterization of two digested sludges sampled in an urban and a peri-urban district, representative models of two scenarios of different anthropic impacts. This study highlighted higher contamination for the sludge derived from the urban area, accounted for by the 4-ring PAHs. In addition, since carcinogenic PAHs were detected, the environmental risk (by mean of the comparison of predicted vs predicted no-effect concentrations) and the carcinogenic human risk from dermal contact (through the calculation of the adsorbed lifetime average daily dose) were assessed in the case of soils amended with the sludges considered, pointing out that the measured concentrations do not pose a risk.

Investigation of the effects of biochar amendment on soil under freeze‒thaw cycles and the underlying mechanism

Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

Biochar Co-Compost: A Promising Soil Amendment to Restrain Greenhouse Gases and Improve Rice Productivity and Soil Fertility

Agriculture is a major source of greenhouse gas (GHG) emissions. Biochar has been recommended as a potential strategy to mitigate GHG emissions and improve soil fertility and crop productivity. However, few studies have investigated the potential of biochar co-compost (BCC) in relation to soil properties, rice productivity, and GHG emissions. Therefore, we examined the potential of BC, compost (CP), and BCC in terms of environmental and agronomic benefits. The study comprised four different treatments: control, biochar, compost, and biochar co-compost. The application of all of the treatments increased the soil pH; however, BC and BCC remained the top performers. The addition of BC and BBC also limited the ammonium nitrogen (NH4+-N) availability and increased soil organic carbon (SOC), which limited the GHG emissions. Biochar co-compost resulted in fewer carbon dioxide (CO2) emissions, while BC resulted in fewer methane (CH4) emissions, which was comparable with BCC. Moreover, BC caused a marked reduction in nitrous oxide (N2O) emissions that was comparable to BCC. This reduction was attributed to increased soil pH, nosZ, and nirK abundance and a reduction in ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) abundance. The application of different amendments, particularly BCC, favored rice growth and productivity by increasing nutrient availability, soil carbon, and enzymatic activities. Lastly, BCC and BC also increased the abundance and diversity of soil bacteria, which favored plant growth and caused a reduction in GHG emissions. Our results suggest that BCC could be an important practice to recycle organic sources while optimizing climate change and crop productivity.

Biochar Amendments and Phytoremediation: A Combined Approach for Effective Lead Removal in Shooting Range Soils.

The increasing contamination of soil with heavy metals poses a problem to environmental sustainability. Among these pollutants, lead is particularly concerning due to its persistence in the environment, with harmful effects on human health and ecosystems. Various strategies that combine phytoremediation techniques with soil amendments have emerged to mitigate lead contamination. In this context, biochar has gained significant attention for its potential to enhance soil quality and remediate metal-contaminated environments. This study aims to investigate the combined effect of biochar amendments on the phytoremediation of lead-contaminated shooting range soils. A series of experiments were conducted to determine the impact of the amount and distribution of biochar on lead removal from soil. Soil samples were incubated with biochar for one week, after which two types of seeds (Brassica rapa and Lolium perenne) were planted. Plant and root lengths, as well as the number of germinated seeds, were measured, and a statistical analysis was conducted to determine the influence of the amendments. After one month, the Pb concentration decreased by more than 70%. Our results demonstrate that seed germination and plant growth were significantly better in soil samples where biochar was mixed rather than applied superficially, with the optimal performance observed at a 10% wt. biochar amendment. Additionally, the combined use of biochar and phytoremediation proved highly effective in immobilizing lead and reducing its bioavailability. These findings suggest that the combination of biochar, particularly when mixed at appropriate concentrations, and Brassica rapa significantly improved lead removal efficiency.

Assessing the Evolution of Stability and Maturity in Co-Composting Sheep Manure with Green Waste Using Physico-Chemical and Biological Properties and Statistical Analyses: A Case Study of Botanique Garden in Rabat, Morocco

Organic waste utilization stands as a pivotal approach to ecological and economic sustainability. This study aimed to assess the stability, maturity, and evolution of co-composts comprising various blends of green waste (GW) and sheep manure (SM). Employing a diverse array of physico-chemical and biological parameters, we investigated the co-composting process over 120 days. Three types of garden waste (mixture of green waste (MGW), fallen leaves (FL), and grass cutting (GC)) were utilized. The results revealed significant compost transformation, evident by odor and insect absence and a shift to dark brown coloration, indicating maturation. The compost C2, derived from FL, exhibited superior soil amendment potential. Significantly, it exhibited a pH level of 6.80, an EC of 2.45 mS/cm, and an OM content of 55%, along with a C/N ratio of 16.15. Analysis of the macronutrients revealed values of 1.98% for TN, 3.22% for TP, and 0.61% for K. Crucially, the compost showed no phytotoxic effects and boasted a high GI of 94.20% and a low respiration rate of 4.02 mg/50 g, indicating its stability and appropriateness for agricultural application. Our findings underscore compost’s potential as an eco-friendly soil amendment, offering valuable insights for sustainable agricultural management and supporting the circular economy.

Soil Localized Leaching and Reclamation with Gypsum and Sulfuric Acid: A Case Study of Pistachio Orchard, Kerman-Iran

ABSTRACT Localized leaching method is a new reclamation leaching technique. Localized leaching method by using drip tapes allows water to be applied directly to the areas of salt accumulation. This study applied localized leaching method on a sandy loam soil in a pistachio orchard in Kerman, Iran to evaluate the impact of three treatments: adding gypsum soil remediation (G), soil remediation with sulfuric acid (SA) andirrigation water (IW) on soil remediation. Three treatments (IW, G and SA) in four repetitions were used to remove soluble salts from the Main Active Root Zone (MARZ) in a pistachio orchard which irrigated by a subsurface irrigation system. The localized leaching method consist of two T-tape pipelines at a distance of 40 cm located on both sides of the tree rows. Soil sampling was carried out before and after leaching from soil unit profiles with 80 cm (Length) × 120 cm (Depth) with 20 cm intervals. Concentrations of sodium (Na), magnesium (Mg), calcium (Ca) cations, and electrical conductivity (EC) were examined before and after leaching process. Results revealed that application of G-treatment compared to IW-treatment and SA-treatment led to more leaching of Na and Mg from the soil by 61% and 50%, respectively. The amount of leached Ca in both G-treatment and SA-treatments was less than that of IW-treatment. The leaching efficiency of total soluble salts for G, IW and SA treatments were 58%, 56% and 45%, respectively. Gypsum application could be recommended as a soil amendment. In addition, the localized leaching technique offers water-saving potential opposed to traditional leaching methods which applying water to the entire field.

Soil fertility and plant nutrition in an organic olive orchard after 5 years of amendment with compost, biochar or their blend

The agronomic use of compost and biochar as soil amendments may exhibit contrasting results in terms of soil fertility and plant nutrition. The effects of the biennial application of biochar, compost and a blend of compost:biochar (90:10; % dw:dw) on the agronomical performance of an organically managed and well established 25-year-old olive orchard was assessed 5 years after the initial application. The agronomical evaluation was based on the assessment of the soil physical, chemical, and biological characteristics, and the assessment of the soil fertility by both crop production and nutritional status of the orchard, and the bioassay with olive plantlets. Biochar mainly benefited the physical properties (bulk density, total porosity, aeration, water retention capacity) of soil, especially in the top 0–5 cm. Compost and its blend with biochar improved microbial activity, soil nutritional status (increasing the content of soluble organic C, N, and P) and favoured the formation of aggregates in soil. The bioassay conducted with young plantlets confirmed the enhanced soil fertility status in the three amended treatments, particularly in the case of biochar and its blend with compost. However, this effect was not significantly observed in the adult plants after 5 years of application, reflecting the slow response of adult olive trees to changes in fertilization. Based on these results, alongside the desirable long-residence time of biochar in soil and the ready availability of compost, the blend of biochar with compost assayed in this study is defined as a valid strategy for preparing high quality soil organic amendments.

Impacts of poultry manure and biochar amendments on the nutrients in sweet potato leaves and the minerals in the storage roots

Poultry manure (PM) has demonstrated its potential to enhance crop nutritional quality. Nevertheless, there remains a dearth of knowledge regarding its synergistic effects when combined with wood biochar (B) on the nutrient concentrations in sweet potato leaves (Ipomoea batatas L.) and the mineral content stored in sweet potato storage roots. Hence, a two-year field trial was undertaken during the 2019 and 2020 cropping seasons in southwestern Nigeria, spanning two locations (Owo—site A and Obasooto—site B), to jointly apply poultry manure and wood biochar as soil amendments aimed at enhancing the nutritional quality of sweet potato crop. Each year, the experiment involved different combinations of poultry manure at rates of 0, 5.0, and 10.0 t ha−1 and biochar at rates of 0, 10.0, 20.0, and 30.0 t ha−1, organized in a 3 × 4 factorial layout. The results of the present study demonstrated that the individual application of poultry manure (PM), biochar (B), or their combination had a significant positive impact on the nutrient composition of sweet potato leaves and minerals stored in the sweet potato storage roots, with notable synergistic effects between poultry manure and biochar (PM × B) in enhancing these parameters. This highlights the potential of biochar to enhance the efficiency of poultry manure utilization and improve nutrient utilization from poultry manure. The highest application rate of poultry manure at 10.0 t ha−1 and biochar at 30.0 t ha−1 (PM10 + B30), resulted in the highest leaf nutrient concentrations and mineral composition compared to other treatments at both sites. Averaged over two years, the highest application rate of poultry manure at 10.0 t ha−1 and biochar at 30.0 t ha−1 (PM10 + B30) significantly increased sweet potato leaf nutrient concentrations: nitrogen by 88.2%, phosphorus by 416.7%, potassium by 123.8%, calcium by 927.3%, and magnesium by 333.3%, compared to those in the control (PM0 + B0). The same treatment increased the concentration of sweet potato root storage minerals: phosphorus by 152.5%, potassium by 77.4%, calcium by 205.5%, magnesium by 294.6%, iron by 268.4%, zinc by 228.6%, and sodium by 433.3%, compared to the control. The highest application rate of poultry manure at 10.0 t ha−1 and biochar at 30.0 t ha−1 yielded the highest economic profitability in terms of gross margin (44,034 US$ ha−1), net return (30,038 US$ ha−1) and return rate or value-to-cost ratio (VCR) (263). The results suggested that the application of poultry manure at 10 t ha−1 and biochar at 30 t ha−1 is economically profitable in the study areas and under similar agroecological zones and soil conditions.