Effects of manure (M), hazelnut husks (HH), tea waste (TEW), and tobacco wastes (TOW) on some soil quality indexes were monitored for more than 2 years in a clay field and a loamy sand field. While soil organic carbon (OC) contents were around 2% after 30 months in clay, they were generally less than 2% after 7 months in loamy sand. Organic wastes generally increased aggregate stability (AS) and field capacity and decreased bulk density (BD) of the soils. Soil pH decreased with TEW and increased with M treatment. Tobacco wastes exerted the greatest effect on AS, EC, and nitrate (NO₃) nitrogen (N). Hazelnut husks and TEW had the greatest effect on soil respiration in clay and loamy sand soils, respectively. While BD and pH increased, the other indicators generally decreased between the first and the last sampling. Soil quality can be improved in coarse-textured soils using TEW and HH and in fine-textured soils using TEW and M.

The remediation of heavy metals (HMs) in soil is always an important topic, as environmental contamination by HMs is of serious concern. Numerous potential advantages, especially integrated with biochar produced from various biomass, might provide an ecologically beneficial tool for achieving the UN’s sustainable development objectives for greener soil remediation. The aim of this study was to address how the soil-science professions may best successfully utilize biochar for greener remediation of HMs-contaminated soils. In this context, the biochar preparation method from different agricultural feedstock, and its use as a soil amendment for remediation of HMs-contaminated soil, were discussed. Furthermore, biochar-based nanocomposites containing functional materials have lately attracted much interest because of the unique properties emerging from their nanoscale size compartment, and present good promise in terms of reactivity and stability. The utility and potency of biochar-based nanocomposites, on the other hand, are determined by their ability to adapt to particular site circumstances and soil qualities. This overview summarized the current advances in the application for the remediation of HMs-polluted soils. Future views on the usage and possibilities for deploying biochar-based nanocomposites in polluted soils were discussed.

In this study, changes in some soil quality indexes in a hazelnut orchard located in the Black Sea Region of Turkey were investigated after 6 months of compost (CMP) and hazelnut husk (HH) applications. CMP and HH applications increased soil organic carbon (OC) content from 1.40% to 2.57 and 3.51%, and electrical conductivity from 0.06 dS m⁻¹ to 0.20 and 0.91 dS m⁻¹, respectively (P < 0.01). In comparison to control treatment, CMP and HH applications increased the sum of exchangeable cations by 31 and 37%, aggregate stability by 2 and 7%, initial infiltration rate by 34 and 436%, and reduced bulk density by 20 and 33%, penetration resistance by 33 and 67%, respectively (P < 0.01). Physical and chemical soil quality parameters were improved using both HH and CMP in the hazelnut orchard. Although both organic matter sources were effective on quality of clay soil, slow mineralization rate of HH in soil due to including the highest C:N ratio (55%) caused greater effects of HH on soil quality indexes than that of CMP (having 22% C:N ratio) after 6 months of application.

This study was carried out to determine the proper amount of application for manure (M), hazelnut husk (Corylus avellane L.) (HH), tobacco (Nicotiana tabacum L.) (TO) and tea (Camellia Sinensis (L.)) (TE) wastes based on hydraulic property improvement of a loamy sand cropland in Turkey. The effects of agricultural wastes on field capacity (FC), permanent wilting point (PWP), available water content (AWC), relative saturation (RS) and initial infiltration rate (IR) were determined for a loamy sand soil 7 months after agricultural wastes were incorporated to 15 cm soil depth at four different rates (0, 2%, 4% and 6%, weight:weight) in a randomized plot design experiment with three replicates. While increases in soil OM content for the M application rates were generally lower, TE and HH treatments including high organic carbon (OC) contents resulted in high soil organic matter (OM) increases. Organic wastes generally increased the values of soil hydraulic properties, with increased aggregate stability (AS) and total porosity (F) and reduced bulk density (BD). The highest AS and F values were obtained with 6% HH and 6% TE applications, respectively. Due to different mineralization rates of the organic wastes attributable to their carbon: nitrogen (C:N) ratios, the same application rate had different effects on the soil’s hydraulic properties. Manure, having the lowest C:N ratio, generally had a lower effect on AS and BD. Increased IR due to increases in AS and F by the agricultural waste treatment, especially at 4 and 6% HH, reduced the AW content to 15 cm compared with 2% HH. This indicates that the significant application of higher C:N ratio wastes is not suitable in terms of AW, due to significant improvement of IR. While the highest FC (17.3%) and AWC (10.7%) values were found in the 6% TE application, the highest PWP (7.2%) and IR (333.4 cm h⁻¹) were in the 6% TO and 6% HH applications, respectively. To improve soil physical and hydraulic properties, 6% TO and M, 4% TE and 2% HH applications are suggested for loamy sand cropland.

Biochar application has gained attention as an effective soil amendment for improving soil quality and increasing crop productivity, particularly in clay-rich soils facing challenges such as compaction, poor drainage, and nutrient limitation. This two-year field study evaluated the effects of fresh and artificially aged biochar on soil chemical, physical, and biological properties and wheat (Triticum aestivum) yield. The experiment was conducted on clay soil with treatments including no biochar application as a control (CK), 5 and 10 t ha⁻¹ fresh biochar (B5, B10) and 5 and 10 t ha⁻¹ aged biochar (AB5, AB10). The results showed significant improvements in soil pH, soil organic carbon, cation exchange capacity, total nitrogen, and plant-available water capacity, particularly with higher doses of biochar. In both years, the effects of the treatments on the soil quality index area (SQI-area) were found to be statistically significant. The AB10 treatment increased SQI-area by 19% compared to the CK in the first year and by 33% in the second year. In the first year, the highest grain yield was obtained from the AB10 treatment, reaching 5.25 t ha⁻¹, which was 13% higher than the CK. In the second year, the highest yield was obtained from the B10 treatment, reaching 4.09 t ha⁻¹, which was 24% higher than the CK. Despite these positive changes, the correlation between SQI and yield was not statistically significant, suggesting that crop yield may also depend on other interacting variables. These results highlight the potential of biochar, particularly aged biochar, as a sustainable practice to improve soil health and productivity in clay soils.