Ana Catarina Bastos

Reductions in soil surface albedo as a function of biochar application rate: implications for global radiative forcing

Biochar can be defined as pyrolysed (charred) biomass produced for application to soils with the aim of mitigating global climate change while improving soil functions. Sustainable biochar application to soils has been estimated to reduce global greenhouse gas emissions by 71‐130 Pg CO2-Ce over 100 years, indicating an important potential to mitigate climate change. However, these estimates ignored changes in soil surface reflection by the application of dark-coloured biochar. Through a laboratory experiment we show a strong tendency for soil surface albedo to decrease as a power decay function with increasing biochar application rate, depending on soil moisture content, biochar application method and land use. Surface application of biochar resulted in strong reductions in soil surface albedo even at relatively low application rates. As a first assessment of the implications for climate change mitigation of these biochar‐albedo relationships, we applied a first order global energy balance model to compare negative radiative forcings (from avoided CO2 emissions) with positive radiative forcings (from reduced soil surface albedos). For a global-scale biochar application equivalent to 120 t ha 1 , we obtained reductions in negative radiative forcings of 5 and 11% for croplands and 11 and 23% for grasslands, when incorporating biochar into the topsoil or applying it to the soil surface, respectively. For a lower global biochar application rate (equivalent to 10 t ha 1 ), these reductions amounted to 13 and 44% for croplands and 28 and 94% for grasslands. Thus, our findings revealed the importance of including changes in soil surface albedo in studies assessing the net climate change mitigation potential of biochar, and we discuss the urgent need for field studies and more detailed spatiotemporal modelling.

A comment on ‘Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis': on the importance of accurate reporting in supporting a fast-moving research field with policy implications

S IMON JEFFERY * , FRANK G .A . VERHE I J EN † , ANA CATAR INA BASTOS † and MARIJN VAN DER VELDE‡ *Soil Biology and Soil Biological Quality Group, Wageningen University, Postbus 47, 6700AA Wageningen, The Netherlands, †Centre for Environmental and Marine Studies (CESAM), University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal, ‡International Institute for Applied Systems Analysis (IIASA), Ecosystems Services and Management Program, Schlossplatz 1, A-2361 Laxenburg, Austria

Sustainability, certification, and regulation of biochar

Biochar has a relatively long half-life in soil and can fundamentally alter soil properties, processes, and ecosystem services. The prospect of global-scale biochar application to soils highlights the importance of a sophisticated and rigorous certification procedure. The objective of this work was to discuss the concept of integrating biochar properties with environmental and socioeconomic factors, in a sustainable biochar certification procedure that optimizes complementarity and compatibility between these factors over relevant time periods. Biochar effects and behavior should also be modelled at temporal scales similar to its expected functional lifetime in soils. Finally, when existing soil data are insufficient, soil sampling and analysis procedures need to be described as part of a biochar certification procedure.

Concise overview of European soil erosion research and evaluation

Abstract Soil loss by erosion is a major threat to European soil resources. It is linked to most other threats to soils and is estimated to incur substantial costs to society. To monitor and evaluate soil erosion comprehensively, measurements and modelled estimates of soil loss by erosion need to integrate water, wind and tillage erosion, as these are common throughout Europe. Tolerable rates of soil erosion (thresholds) in Europe can be set equal to estimated soil formation rates, that is, ~1 t ha−1 yr−1, but defining this threshold will require further research in the context of soil functions. There is a strong need for improving the knowledge base of current erosion rates, especially to develop and validate reliable erosion prediction models. This should include depositional environments (e.g. flood plains) where greater erosion rates than those on hill slopes may be tolerable, depending on the consequent effects on all relevant ecosystem goods and services provided by soil. Moreover, in considering erosion at catchment (watershed) level, the distance between erosion sites and areas of deposition should be taken into account.

Biochars in soils: towards the required level of scientific understanding

Key priorities in biochar research for future guidance of sustainable policy development have been identified by expert assessment within the COST Action TD1107. The current level of scientific understanding (LOSU) regarding the consequences of biochar application to soil were explored. Five broad thematic areas of biochar research were addressed: soil biodiversity and ecotoxicology, soil organic matter and greenhouse gas (GHG) emissions, soil physical properties, nutrient cycles and crop production, and soil remediation. The highest future research priorities regarding biochar’s effects in soils were: functional redundancy within soil microbial communities, bioavailability of biochar’s contaminants to soil biota, soil organic matter stability, GHG emissions, soil formation, soil hydrology, nutrient cycling due to microbial priming as well as altered rhizosphere ecology, and soil pH buffering capacity. Methodological and other constraints to achieve the required LOSU are discussed and options for efficient progress of biochar research and sustainable application to soil are presented.

Simulated post-fire temperature affects germination of native and invasive grasses in cerrado (Brazilian savanna).

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 °C. Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses. Methods: Seeds were stored at alternating temperatures of 45 ºC/10 ºC (10 h/14 h) for 7 d or 30 d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30 d. Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 ºC/10 ºC) after 7 d, with significant reduction in the germination time after 30 d. Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.

The different faces of biochar: contamination risk versus remediation tool

This article reviews the different aspects of biochar as source and sink of organic and inorganic contaminants. Biochar can contain organic contaminants such as polycyclic aromatic hydrocarbons or ...

Representativeness of European biochar research: Part I–field experiments

A representativeness survey of existing European Biochar field experiments within the Biochar COST Action TD1107 was conducted to gather key information for setting up future experiments and collaborations, and to minimise duplication of efforts amongst European researchers. Woody feedstock biochar, applied without organic or inorganic fertiliser appears over-represented compared to other categories, especially considering the availability of crop residues, manures, and other organic waste streams and the efforts towards achieving a zero waste economy. Fertile arable soils were also over-represented while shallow unfertile soils were under-represented. Many of the latter are likely in agroforestry or forest plantation land use. The most studied theme was crop production. However, other themes that can provide evidence of mechanisms, as well as potential undesired side-effects, were relatively well represented. Biochar use for soil contamination remediation was the least represented theme; further work is needed to identify which specific contaminants, or mixtures of contaminants, have the potential for remediation by different biochars.

A comment on the Editorial “Replication in aquatic biology: The result is often pseudoreplication”

In a recent Editorial, the Editors revisited the issue of pseudo)replication in scientific studies, expressing insightful opinon in the context of aquatic biology and related disciplines Nikinmaa et al., 2012). Appreciatively, they invited the readers o submit their own judgement and ultimately, “contributions that onclusively show errors in [. . .] above thinking”, as a means of genrating positive discussion on such a hot topic. Here we provide our hands-on’ view on (pseudo)replication, in the light of what we conider to be a more practical and relative concept than that described y a number of authors. We thus, encourage our comments not to e perceived as yet another review on pseudoreplication or one ore piece of criticism (otherwise seemingly ‘wore out’) to fellow eers who one might find as lacking “of appreciation [. . .] of basic tatistical issues” (Heffner et al., 1996). Subsequently, we address he series of concerns posed by the Editors as specific discussion oints, where we have identified potential overgeneralization and onsequently, the possibility for misinterpretation by the readers. n this context, we present and discuss examples that illustrate raditionally accepted premises of scientific method. The term ‘pseudoreplication’ has seen overwhelming popularty ever since Hurlbert (1984) released his distinctive review and ritique to ecologist peers, in the matters of misconceptions in xperimental design and misuse of statistical treatments. Such an ssay has certainly raised the standards for any study of the natral environment, as well as set guidelines for the more aware esearchers, editors and reviewers. For the purpose of this disussion, we address ‘replication’ as expressed by Drummond and owler (2012), hereby consisting of the qualitative or quantitative escription of “more than one individual from within an experiental unit, which has been given the same treatment, or has been xposed to the same fixed effects, or has been drawn from the same roup”. Expectedly, there is a certain degree of variability within ach experimental unit (e.g. a group of individuals), although such ntra-variability is far smaller than that expected among different xperimental units. In other words, one expects a certain degree of ariation in replicate measurements and hence the more replicates ne uses, the more representative is one’s grasp about the experiental unit. Despite this legitimate assumption, it is perhaps less easonable to think that such a variation could be fully explained by andom sampling. So-called ‘pseudoreplication’ arises when ranom sampling is restricted by whichever reason. We are all part f an overwhelmingly variable universe, thus yes, sampling that is ruly random is not often achieved and the result might be seen s pseudoreplication, at some level. The question is not on whether his is important (undoubtedly it is), but rather on when it is imporant and on how does that importance relate to other features of xperimental design and statistical analyses.

Representativeness of European biochar research: part II – pot and laboratory studies

Biochar research is extensive and there are many pot and laboratory studies carried out in Europe to investigate the mechanistic understanding that govern its impact on soil processes. A survey was conducted in order to find out how representative these studies under controlled experimental conditions are of actual environmental conditions in Europe and biomass availability and conversion technologies. The survey consisted of various key questions related to types of soil and biochar used, experimental conditions and effects of biochar additions on soil chemical, biological and physical properties. This representativeness study showed that soil texture and soil organic carbon contents used by researchers are well reflected in the current biochar research in Europe (through comparison with published literature), but less so for soil pH and soil type. This study provides scope for future work to complement existing research findings, avoiding unnecessary repetitions and highlighting existing research gaps.