Johannes Lehmann

Biochar can have effects on soil biota that are distinct from the effects of other organic matter in soils. This chapter discusses the principles by which biochars affect the community composition, activity, and functioning of soil microorganisms and fauna. Surface properties of biochar, its mineral and organic functional groups, pore structure, specific organic compounds, and metabolizable substrates may all have direct and indirect effects on soil biota, which are described in detail.

Biochar science has advanced significantly in the past few years, but there are still knowledge gaps that need to be filled, such as the lack of a decision tool to identify the most suitable biochar for specific soils, materials, and environmental constraints. Therefore, experimental designs should be carefully planned, and comparisons should be made with standard biochar, a control without biochar, or equivalent amounts of carbon as crop residues or composts. Relevant knowledge gaps may need to be addressed by experimentation at the implementation scale, notably in the area of life cycle evaluation of their full environmental impact, socio-economic evaluation, and production technology. The large variety of possible biochar products requires due diligence of the supply chain to discover unintended consequences, and regulatory frameworks must be in place to provide incentives and point out limits. Scaling …

Biochar is a relatively new development in sustainable agricultural management that can be applied to ameliorate degraded and less fertile soils, especially sandy-textured ones, to improve their productivity with respect to crop production through improved nutrient availability. However, as the literature has shown, the response of sandy-textured soils to biochar varies in terms of effect size and direction. Therefore, the present study systematically reviewed the available evidence to synthesize the impact of biochar amendments on aspects of the nutrient cycle of sandy-textured soils. Both peer-reviewed and gray literature were searched in English in bibliographic databases, organizational web pages, and Internet search engines. Articles underwent a two-stage screening (title and abstract, and full-text) based on predefined criteria, with consistency checks. Validity assessments were conducted, utilizing specifically designed tools for study validity. Data extraction involved categorizing the various properties of the nutrient cycle into nine main Soil and Plant Properties (SPPs), each of which was studied independently. Nine meta-analyses were performed using a total of 1609 observations derived from 92 articles. Comparing meta-averages with and without correction for publication bias suggests that publication bias plays a minor role in the literature, while some indication for publication bias is found when accounting for heterogeneity by means of meta-regressions. According to the results, soil total and available nitrogen [N], phosphorous [P] and potassium [K], plant nutrient level, and potential cation exchange capacity (CEC) increased by 36% (CI …

Soil organic matter (SOM) is extremely complex because of the variety of its inputs (e.g., plant tissues, microorganisms, animals, exogenous organic matter) and their different stages of decomposition. This chapter presents methods designed for the characterization of its composition and turnover at contrasting scales. To separate different SOM pools (either chemically, thermally, or physically), fractionation methods can be used to separate meaningful subsets of SOM. The chemical composition of whole SOM or SOM fractions can be characterized with spectroscopic methods that do not require prior extraction of SOM. The study of specific components requires the utilization of wet chemical methods. Visualization methods allow for identification of the location of SOM within soil structure and deciphering of its interaction with soil minerals, even at nanometer scales. The dynamics of SOM can be determined by …

Manure-derived biochars have a fertilizer potential as pyrolysis concentrates non-volatile nutrients. The addition of magnesium (Mg) to poultry manure enhances its Mg/Ca ratio and could increase soluble P by phosphate-solubilizing bacteria (PSB). Our objective was to assess the potential of PSB strains to solubilize P from both unenriched and Mg-enriched biochar and to evaluate the growth of maize in an Oxisol fertilized with biochar (100 mg kg− 1 total P) to satisfy plant P needs. We examined the strains: Paraburkholderia fungorum UFLA 04–155, Pseudomonas anuradhapurensis UFPI B5-8A, Paenibacillus chondroitinus UFLA 03–116, Acinetobacter pittii UFLA 03–09, and Rhizobium tropici CIAT 899. Biochar was made from poultry manure at temperatures of 350 C, 500 C, and 650 C. Maize growth and P uptake were assessed in plants after 15 and 30 days under greenhouse conditions. The strain P …

In their commentary, Xiao et al.[1] cautioned that the conclusions on the critical role of microbial carbon use efficiency (CUE) in global soil organic carbon (SOC) storage in the paper by Tao et al.[2] might be too simplistic. TheyclaimedthatTaoetal.’sstudylacked mechanistic consideration of SOC formation and excluded important data sets. Xiao et al. brought up important points, which can be largely reconciled with our findings by understanding the differences in expressing processes in empirical studies and in models.Mechanistic understanding of complex processes from empirical research is usually translated into mathematical models with some level of simplification. For example, processes involved in SOC stabilization and persistence, as brought up by Xiao et al., were considered using the model and evaluated together with microbial CUE for their relative importance to global SOC storage in Tao et al.[2]. The …

Understanding the formation and stabilization mechanisms of soil organic carbon (SOC) is important for managing land carbon (C) and mitigating climate change. Tao et al. 1 reported that microbial C use efficiency (CUE) is the primary determinant of global SOC storage and that the relative impact of plant C inputs on SOC is minor. Although soil microbes undoubtedly play an important role in SOC cycling, we are concerned about the robustness of the approach taken by Tao et al. 1. The potential biases in their analyses may lead to misleading, model-dependent results.An important piece of evidence in support of an empirical relationship between CUE and SOC stems from a meta-analysis based on 132 paired CUE and SOC measurements. Tao et al. 1 applied a linear mixed-effects model to this dataset that included CUE, mean annual temperature (MAT), soil depth and random effects and explained 55% of the …

Biochar amendments add persistent organic carbon to soil and can stabilize rhizodeposits and existing soil organic carbon (SOC), but effects of biochar on subsoil carbon stocks have been overlooked. We quantified changes in soil inorganic carbon (SIC) and SOC to 2 m depth 10 years after biochar application to calcareous soil. The total soil carbon (i.e., existing SOC, SIC, and biochar-C) increased by 71, 182, and 210% for B30, B60, and B90, respectively. Biochar application at 30, 60, and 90 t ha–1 rates significantly increased SIC by 10, 38, and 68 t ha–1, respectively, with accumulation mainly occurring in the subsoil (below 1 m). This huge increase of SIC (mainly CaCO3) is ∼100 times larger than the inorganic carbon present in the added biochar (0.3, 0.6, or 0.9 t ha–1). The benzene polycarboxylic acid method showed that the biochar-amended soil contained more black carbon particles (6.8 times higher …