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Various studies have established that feedstock choice, pyrolysis temperature, and pyrolysis type influence final biochar physicochemical characteristics. However, overarching analyses of pre-biochar creation choices and correlations to biochar characteristics are severely lacking. Thus, the objective of this work was to help researchers, biochar-stakeholders, and practitioners make more well-informed choices in terms of how these three major parameters influence the final biochar product. Utilizing approximately 5400 peer-reviewed journal articles and over 50,800 individual data points, herein we elucidate the selections that influence final biochar physical and chemical properties, total nutrient content, and perhaps more importantly tools one can use to predict biochar’s nutrient availability. Based on the large dataset collected, it appears that pyrolysis type (fast or slow) plays a minor role in biochar physico- (inorganic) chemical characteristics; few differences were evident between production styles. Pyrolysis temperature, however, affects biochar’s longevity, with pyrolysis temperatures > 500 °C generally leading to longer-term (i.e., > 1000 years) half-lives. Greater pyrolysis temperatures also led to biochars containing greater overall C and specific surface area (SSA), which could promote soil physico-chemical improvements. However, based on the collected data, it appears that feedstock selection has the largest influence on biochar properties. Specific surface area is greatest in wood-based biochars, which in combination with pyrolysis temperature could likely promote greater changes in soil physical characteristics over other feedstock-based biochars. Crop- and other grass-based biochars appear to have cation exchange capacities greater than other biochars, which in combination with pyrolysis temperature could potentially lead to longer-term changes in soil nutrient retention. The collected data also suggest that one can reasonably predict the availability of various biochar nutrients (e.g., N, P, K, Ca, Mg, Fe, and Cu) based on feedstock choice and total nutrient content. Results can be used to create designer biochars to help solve environmental issues and supply a variety of plant-available nutrients for crop growth.

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Maize (Zea mays L., line F2) plants were grown in the field under high or low fertilization input to monitor the metabolic, biochemical and molecular events occurring in young vegetative leaves and in the different leaf stages along the main axis in plants harvested 15 days after silking. This study shows that in maize which possess large sinks represented by the seeds, nitrogen (N) management is different compared with tobacco in which sink strength is much lower and mostly limited to young developing leaves. Although in young leaves nitrate assimilation predominates in both species, ammonium assimilation exhibits some species‐specific differences with respect to inorganic and organic N metabolite accumulation during leaf ageing. These differences are likely to be related to the high sink strength of the ear in maize, which continuously imports carbon and N assimilates during grain filling. Consequently, a number of cytosolic glutamine synthetase isoenzymes are expressed during leaf ageing to maintain a constant flux of reduced N necessary for the synthesis of organic N molecules used either for leaf protein synthesis or directly translocated to the grain. This situation contrasts with that found in tobacco for which leaf ammonium assimilation in the plastids is shifted to the cytosol during the transition from sink leaves to source leaves. These species‐specific differences for N assimilation and recycling are discussed in relation to the evolution of leaf photosynthetic activity and leaf senescence, which both seem to be largely dependent on the different sink strength in each species.

Agriculture and land use change has significantly increased atmospheric emissions of the non-CO2 green-house gases (GHG) nitrous oxide (N2O) and methane (CH4). Since human nutritional and bioenergy needs continue to increase, at a shrinking global land area for production, novel land management strategies are required that reduce the GHG footprint per unit of yield. Here we review the potential of biochar to reduce N2O and CH4 emissions from agricultural practices including potential mechanisms behind observed effects. Furthermore, we investigate alternative uses of biochar in agricultural land management that may significantly reduce the GHG-emissions-per-unit-of-product footprint, such as (i) pyrolysis of manures as hygienic alternative to direct soil application, (ii) using biochar as fertilizer carrier matrix for underfoot fertilization, biochar use (iii) as composting additive or (iv) as feed additive in animal husbandry or for manure treatment. We conclude that the largest future research needs lay in conducting life-cycle GHG assessments when using biochar as an on-farm management tool for nutrient-rich biomass waste streams.

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