Kurt A. Spokas

Bio: Kurt A. Spokas is an academic researcher from United States Department of Agriculture. The author has contributed to research in topics: Biochar & Soil water. The author has an hindex of 51, co-authored 171 publications receiving 10661 citations. Previous affiliations of Kurt A. Spokas include Princeton University & Argonne National Laboratory.

Review of the stability of biochar in soils: predictability of O:C molar ratios

Abstract: Biochar is not a structured homogeneous material; rather it possesses a range of chemical structures and a heterogeneous elemental composition. This variability is based on the conditions of pyrolysis and the biomass parent material, with biochar spanning the range of various forms of black carbon. Thereby, this variability induces a broad spectrum in the observed rates of reactivity and, correspondingly, the overall chemical and microbial stability. From evaluating the current biochar and black carbon degradation studies, there is the suggestion of an overall relationship in biochar stability as a function of the molar ratio of oxygen to carbon (O:C) in the resulting black carbon. In general, a molar ratio of O:C lower than 0.2 appears to provide, at minimum, a 1000-year biochar half-life. The O:C ratio is a function of production temperature, but also accounts for other impacts (e.g., parent material and post-production conditioning/oxidation) that are not captured solely with production temperature. Th...

Biochar: a synthesis of its agronomic impact beyond carbon sequestration.

Abstract: Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.

Impacts of Sixteen Different Biochars on Soil Greenhouse Gas Production

Abstract: One potential abatement strategy to increasing atmospheric levels of carbon dioxide (CO 2 ) is to sequester atmospheric CO 2 captured through photosynthesis in biomass and pyrolysed into a more stable form of carbon called biochar. We evaluated the impacts of 16 different biochars from different pyrolysis/gasification processes and feed stock materials (corn stover, peanut hulls, macadamia nut shells, wood chips, and turkey manure plus wood chips) as well as a steam activated coconut shell charcoal on net CO 2 , methane (CH 4 ) and nitrous oxide (N 2 O) production/consumption potentials through a 100 day laboratory incubation with a Minnesota agricultural soil (Waukegan silt loam, total organic carbon = 2.6%); Wisconsin forest nursery soil (Vilas loamy sand, total organic carbon = 1.1%); and a California landfill cover soil (Marina loamy sand plus green waste-sewage sludge, total organic carbon = 3.9%) at field capacity (soil moisture potential = -33 kPa). After correcting for the CO 2 , CH 4 and N 2 O production of the char alone, the addition of biochars (10% w/w) resulted in different responses among the soils. For the agricultural soil, five chars increased, three chars reduced and eight had no significant impact on the observed CO 2 respiration. In the forest nursery soil, three chars stimulated CO 2 respiration, while the remainder of the chars suppressed CO 2 respiration. In the landfill cover soil, only two chars increased observed CO 2 respiration, with the remainder exhibiting lower CO 2 respiration rates. All chars and soil combinations resulted in decreased or unaltered rates of CH 4 oxidation, with no increases observed in CH 4 oxidation or production activity. Biochar additions generally suppressed observed N 2 O production, with the exception being high nitrogen compost-amended biochar, which increased N 2 O production. The general conclusions are: (1) the impact on trace gas production is both dependent on the biochar and soil properties and (2) biochar amendments initially reduce microbial activity in laboratory incubations. These preliminary results show a wide diversity in biochar properties that point to the need for more research. Permanent URL: http://hdl.handle.net/2047/d10019583

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Biochar effects on soil biota – A review

Abstract: Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the effects of biochar on soil biota have received much less attention than its effects on soil chemical properties. A review of the literature reveals a significant number of early studies on biochar-type materials as soil amendments either for managing pathogens, as inoculant carriers or for manipulative experiments to sorb signaling compounds or toxins. However, no studies exist in the soil biologyliterature that recognize the observed largevariations ofbiochar physico-chemical properties. This shortcoming has hampered insight into mechanisms by which biochar influences soil microorganisms, fauna and plant roots. Additional factors limiting meaningful interpretation of many datasets are the clearly demonstrated sorption properties that interfere with standard extraction procedures for soil microbial biomass or enzyme assays, and the confounding effects of varying amounts of minerals. In most studies, microbial biomass has been found to increase as a result of biochar additions, with significant changes in microbial community composition and enzyme activities that may explain biogeochemical effects of biochar on element cycles, plant pathogens, and crop growth. Yet, very little is known about the mechanisms through which biochar affects microbial abundance and community composition. The effects of biochar on soil fauna are even less understood than its effects on microorganisms, apart from several notable studies on earthworms. It is clear, however, that sorption phenomena, pH and physical properties of biochars such as pore structure, surface area and mineral matter play important roles in determining how different biochars affect soil biota. Observations on microbial dynamics lead to the conclusion of a possible improved resource use due to co-location of various resources in and around biochars. Sorption and therebyinactivation of growth-inhibiting substances likelyplaysa rolefor increased abundance of soil biota. No evidence exists so far for direct negative effects of biochars on plant roots. Occasionally observed decreases in abundance of mycorrhizal fungi are likely caused by concomitant increases in nutrient availability,reducing theneedfor symbionts.Inthe shortterm,therelease ofavarietyoforganic molecules from fresh biochar may in some cases be responsible for increases or decreases in abundance and activity of soil biota. A road map for future biochar research must include a systematic appreciation of different biochar-types and basic manipulative experiments that unambiguously identify the interactions between biochar and soil biota.

Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review

Abstract: Natural organic biomass burning creates black carbon which forms a considerable proportion of the soil’s organic carbon. Due to black carbon’s aromatic structure it is recalcitrant and has the potential for long-term carbon sequestration in soil. Soils within the Amazon-basin contain numerous sites where the ‘dark earth of the Indians’ (Terra preta de Indio, or Amazonian Dark Earths (ADE)) exist and are composed of variable quantities of highly stable organic black carbon waste (‘biochar’). The apparent high agronomic fertility of these sites, relative to tropical soils in general, has attracted interest. Biochars can be produced by ‘baking’ organic matter under low oxygen (‘pyrolysis’). The quantities of key mineral elements within these biochars can be directly related to the levels of these components in the feedstock prior to burning. Their incorporation in soils influences soil structure, texture, porosity, particle size distribution and density. The molecular structure of biochars shows a high degree of chemical and microbial stability. A key physical feature of most biochars is their highly porous structure and large surface area. This structure can provide refugia for beneficial soil micro-organisms such as mycorrhizae and bacteria, and influences the binding of important nutritive cations and anions. This binding can enhance the availability of macro-nutrients such as N and P. Other biochar soil changes include alkalisation of soil pH and increases in electrical conductivity (EC) and cation exchange capacity (CEC). Ammonium leaching has been shown to be reduced, along with N2O soil emissions. There may also be reductions in soil mechanical impedance. Terra preta soils contain a higher number of ‘operational taxonomic units’ and have highly distinctive microbial communities relative to neighbouring soils. The potential importance of biochar soil incorporation on mycorrhizal fungi has also been noted with biochar providing a physical niche devoid of fungal grazers. Improvements in soil field capacity have been recorded upon biochar additions. Evidence shows that bioavailability and plant uptake of key nutrients increases in response to biochar application, particularly when in the presence of added nutrients. Depending on the quantity of biochar added to soil significant improvements in plant productivity have been achieved, but these reports derive predominantly from studies in the tropics. As yet there is limited critical analysis of possible agricultural impacts of biochar application in temperate regions, nor on the likelihood of utilising such soils as long-term sites for carbon sequestration. This review aims to determine the extent to which inferences of experience mostly from tropical regions could be extrapolated to temperate soils and to suggest areas requiring study.