| • | Biochar recalcitrance and biodegradability (measured by thermal analysis) was unaltered by 7 years of field weathering. |
| • | Aromaticity of biochar-derived dissolved organic matter increased with weathering time. |
| • | There is little-to-no change in biochar C sequestration potential during short-term (years) weathering. |
Biochar has been touted as a long-term carbon sequestration tool. However, there are no studies evaluating biochar’s effect on oxygen (O2) consumption as a measure of the microbial respiration response to biochar. To gain insight into this aspect, we evaluated O2 consumption rates to test the hypothesis that biochar is an efficient agent for carbon dioxide (CO2) sequestration in soils. Four different biochar types and one activated charcoal were incubated alone and associated with three different soils for approximately 2 months in laboratory incubations. Headspace concentration of CO2 and O2 was periodically quantified. The data presented here confirm that the CO2 production following biochar’s addition to soils results in a process that is correlated to oxygen consumption. However, this overall stimulation is not clearly related to biochar type. Activated carbon resulted in the highest statistically significant stimulation of activity, despite it possessing the lowest quantity of volatile carbon and mineral nutrient sources. Taking into consideration our results, we conclude that using biochar does achieve total carbon sequestration. However, the amount of available soil organic carbon following soil incorporation appears to be reduced following biochar addition and its long-term implication on this mineralizable soil organic carbon pool does deserve more research attention.
Pyrolysis is an option for enhancing the sustainable management of broiler manure surpluses by producing a concentrated, hygienic char product with a fertilizer and soil conditioner value. In this study, the impacts of pyrolysis conducted at 350, 400 and 450 °C on total nutrient and harmful element concentrations in biochars derived from peat-bedded broiler manure were examined. Emphasis was placed on the availability of phosphorus (P). In addition, the pore structures of these biochars were explored using X-ray microtomography and image analysis. During pyrolysis, 35–50%, 40–55% and 35–45% of the original carbon, nitrogen and sulfur contents, respectively, of the feedstock biomass were lost as volatiles. Mineral elements, including P, were concentrated in the biochar. Although water-extractable P was found to be converted to less labile forms due to charring, the concentration effect and notable increase in sodium bicarbonate-extractable P rendered broiler manure biochars richer in total labile P in comparison with feedstock manure (7.1, 10.0, 11.1 and 14.8 g labile P kg−1 in feedstock and biochars produced at 350, 400 and 450 °C, respectively). The pore volume of the micrometer-scale porosity of the broiler manure biochar was comparable to that found earlier in wood-based biochars. In comparison with wood-based biochars, the pore structure of broiler manure biochars was more versatile, and the pore size distribution was wider. Consequently, part of the porosity was too large to store plant-available water, which may reduce the potential of broiler manure biochars to improve soil water storage capacity.
| • | Application of DMP and DM significantly increased the labile C fractions at both the landscape positions. |
| • | DM and DMP application increased the soil enzymatic activities. |
| • | DM and DMP treatments significantly increased the soil microbial community structure. |
The forms of phosphorus (P) in animal manure and peat are different from synthetic P fertilizers and will affect soil P fractions when they are used as P amendments. Effects of chicken manure (CMB) and peat (PB) derived biochars (CMB and PB) alone or in combination with P fertilizer (KH2PO4) and rock phosphate (RP) on plant/soil health and soil P fractions in an acidic ultisol were examined with greenhouse pot experiments. The total P rate was constant at 120 mg kg−1 in all treatments. Soil P fractions, P uptake, and maize growth were determined after 56 days. Application of CMB combined with P fertilizer or alone significantly increased soil pH, water extractable and relatively labile P, dry matter yield of maize, chlorophyll contents in maize leaves, while decreasing the Fe and Al binding P. Moreover, sole application of CMB and PB showed greater effects than application of P fertilizer alone regarding plant growth and P fractionation. Integration of synthetic inorganic P sources with CMB or sole application of CMB is more beneficial than application of inorganic P sources to improve plant growth and P availability.
Biochar is considered as a good metal sequester and ameliorates the metal toxicity and uptake in plants. However, its effectiveness over other organic amendments is not well discussed. The aim of this study is to compare the biochar amendments alleviating the levels of Pb and Cd in Withania somnifera L. Dunal with other organic manure. Farmyard manure, vermicompost, and biochar were applied in the field spiked with highly available Pb and Cd. Metal bioavailability and accumulation, plant growth and plant physiology, antioxidant enzymes and metabolite content of W. somnifera along with soil properties were evaluated in all treatments. Study indicates that the application of organic manures significantly alleviated the metal levels (33–72%) in the plant in comparison with control. The herbage yield was significantly higher (33–69%) under different organic manures as compared to the metal treatments. Secondary metabolite contents and antioxidant enzymes were higher in metal treatments in comparison with control. Organic manures were not only able to restrain the Pb and Cd in soil but also enhanced the soil microbial activities. Results indicate that biochar amendments were more promising than farmyard manure and vermicompost due to the presence of more stable carbon in biochar and more alleviation in metal uptake. In addition, net profit in the cultivation of W. somnifera was higher for biochar amendments (50% higher) compared to control. The study recommended that biochar could be a better option for commercial and safer production of W. somnifera.
Despite an abundance of short-term studies focusing on biochar’s effects on annual plants, the long-term effects of biochar on perennial plants and the effects of the biochar on the mobility and speciation changes of metals/metalloids not limited to main plant nutrients in soils are poorly constrained. This study reports on the amelioration a sloped orthic ferralsol by biochar from Tibouchina wood and the resulting effects on perennial crops and microbiota, including a comprehensive analysis of metals/metalloids speciation changes. Fields were amended with biochar and urine-amended biochar (2 kg/m2) and were planted with papaya, banana, and manioc. Soil and plant materials were analyzed using acid digestions, sequential extractions, and 16S rRNA gene sequencing. Biochar applications led to decreased soil acidity, shifted the cation exchange capacity from being Al-influenced to being Mg/K/Ca-dominated, and elevated the concentrations of Mg, K, Ca, Zn, and Ba in soils. The exchangeable/acid-soluble fraction of Ca, P, and S notably increased. The soil microbial biome became more species rich and diverse in the biochar-amended fields. Manioc benefited from biochar applications, demonstrating increased growth, which resulted in generally decreased concentrations of trace elements in most plant parts, however, with an increased total elemental uptake. Urine amendment contributed to higher concentrations of P, S, and K in soils, but did not further increase plant growth. Biochar was shown to be a promising soil amendment for agricultural use of orthic ferralsols of the Brazil’s Atlantic forest region, but the accumulation of potentially harmful metals needs to be considered.
Feedstock sources and pyrolysis temperatures affect the physicochemical and morphological properties of biochars. We evaluated biochars derived from switchgrass (SGB) and poultry litter (PLB) pyrolyzed at 350 °C (SGB350, PLB350) and 700 °C (SGB700, PLB700) to identify their potential ability in improving soil health. Except for SGB350, the pH of biochars was high (> 10.0) and can be used as an amendment in acid soils. PLB700 had higher mineral content and nutrient availability due to its higher ash content (tenfold higher) and electrical conductivity. Surface functional groups responsible for metal retention were evidenced in all biochars. Cation exchange capacity (CEC), specific surface area (SSA), and microporosity more than doubled by increasing pyrolysis temperature from 350 to 700 °C. The pH-buffering capacity measured through acid titration curve was better than that calculated with acid/alkali additions. Biochars pyrolyzed at 700 °C have much higher pH, CEC, SSA, and stronger buffering capacity, and thus are more promising to improve soil health and reduce contaminant bioavailability.