Evelyn S. Krull

Importance of mechanisms and processes of the stabilisation of soil organic matter for modelling carbon turnover

This paper reviews current knowledge of soil organic carbon (SOC) dynamics with respect to physical protection, soil moisture and temperature, and recalcitrant carbon fractions (such as charcoal) in predominantly agricultural soils. These factors are discussed within the framework of current soil organic matter models. The importance of soil structure in the stabilisation of organic residues through physical protection has been documented previously in various studies. In addition, changes in soil structure associated with tillage can significantly affect soil organic matter decomposition rates. The concept of physical protection has been incorporated into several soil carbon models as a function of soil texture. While soil texture can affect the soils capacity for aggregation and adsorption, factors such as soil moisture and temperature may further enhance or reduce the extent of physical protection. While adsorption and aggregation can slow decomposition processes, it is unlikely that these processes are solely responsible for the high mean residence times measured in biologically active surface soils. Accordingly, chemical recalcitrance appears to be the only mechanism by which soil organic carbon can be protected for long periods of time.

Biochar application to soil: agronomic and environmental benefits and unintended consequences.

Abstract Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment. The published reviews on biochar application to soil have so far focused mainly on the agronomic benefits, and have paid little attention to the potential unintended effects. The purpose of this chapter is to provide a balanced perspective on the agronomic and environmental impacts of biochar amendment to soil. The chapter highlights the physical and chemical characteristics of biochar, which can impact on the sorption, hence efficacy and biodegradation, of pesticides. As a consequence, weed control in biochar-amended soils may prove more difficult as preemergent herbicides may be less effective. Since biochars are often prepared from a variety of feedstocks (including waste materials), the potential introduction of contaminants needs to be considered before land application. Metal contaminants, in particular, have been shown to impact on plant growth, and soil microbial and faunal communities. Biochar has also been shown to influence a range of soil chemical properties, and rapid changes to nutrient availability, pH, and electrical conductivity need to be carefully considered to avoid unintended consequences for productivity. This chapter highlights some key areas of research which need to be completed to ensure a safe and sustainable use of biochar. In particular, understanding characteristics of biochars to avoid ecotoxicological impacts, understanding the effects of biochar on nutrient and contaminant behavior and transport, the effects of aging and the influence of feedstock and pyrolysis conditions on key properties are some of the areas that require attention.

δ13C depth profiles from paleosols across the Permian-Triassic boundary: Evidence for methane release

Stable carbon isotopic analyses of organic carbon (δ 13 C) in individual paleosol profiles from Permian–Triassic sequences of Antarctica reveal systematic isotopic variations with profile depth. These variations are in many cases analogous to those in modern soils, which are functions of redox conditions, soil development, and degree and type of microbial decay. In modern soils, these isotopic depth functions develop independently from vegetation changes (C 3 versus C 4 vegetation) and can be diagnostic of soil orders. This study shows that soil-intrinsic functions can be preserved in the δ 13 C values of paleosols as old as 260 Ma and constitute valuable data for paleoecological interpretations. A large carbon isotopic offset of as much as 10‰ in whole paleosol profiles across the Permian-Triassic boundary indicates significant changes in the soil biogeochemistry and the soil-atmosphere system. Early Triassic paleosols are distinctive in their extremely low δ 13 C values (to −42‰) and often show an anomalous δ 13 C depth distribution compared to both Permian paleosols and modern soils. Highly depleted δ 13 C values, as the ones in Early Triassic paleosols, are suggested to be associated with microbial methane oxidation (methanotrophy). This hypothesis implies increased methane concentrations in the Early Triassic soil-atmosphere system. Increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the Permian–Triassic boundary.

Characteristics of biochar: organo-chemical properties

Preface Foreword by Tim Flannery 1. Biochar for Environmental Management: An Introduction 2. Physical Properties of Biochar 3. Characteristics of Biochar: Microchemical Properties 4. Characteristics of Biochar: Organo-chemical Properties 5. Biochar: Nutrient Properties and Their Enhancement 6. Characteristics of Biochar: Biological Properties 7. Developing a Biochar Classification and Test Methods 8. Biochar Production Technology 9. Biochar Systems 10. Changes of Biochar in Soil 11. Stability of Biochar in Soil 12. Biochar Application to Soil 13. Biochar and Emissions of Non-CO2 Greenhouse Gases from Soil 14. Biochar Effects on Soil Nutrient Transformations 15. Biochar Effects on Nutrient Leaching 16. Biochar and Sorption of Organic Compounds 17. Test Procedures for Determining the Quantity of Biochar within Soils 18. Biochar, Greenhouse Gas Accounting and Emissions Trading 19. Economics of Biochar Production, Utilization and Greenhouse Gas Offsets 20. Socio-economic Assessment and Implementation of Small-scale Biochar Projects 21. Taking Biochar to Market: Some Essential Concepts for Commercial Success 22. Policy to Address the Threat of Dangerous Climate Change: A Leading Role for Biochar Index

Stable carbon isotope stratigraphy across the Permian–Triassic boundary in shallow marine carbonate platforms, Nanpanjiang Basin, south China

A distinct negative δ13C excursion is documented in two Permian–Triassic sections (Heping and Taiping) in shallow marine carbonate platform deposits in the Nanpanjiang Basin, south China. These sections span from the Changhsingian to the Dienerian and are characterized by a distinct marine boundary facies change from massive, skeletal lime packstone in the Changhsingian to distinctive calcimicrobial framestone in the Griesbachian Hindeodus parvus Zone. The δ13Corg and δ13Ccarb excursions occur directly after the onset of the calcimicrobial framestone (herein termed the ‘Permian–Triassic boundary event’) and before the first occurrence of H. parvus. The isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon (TOC) content. The shift towards depleted values in δ13Corg and δ13Ccarb at the Permian–Triassic boundary event, together with low TOC contents, persists throughout the Griesbachian H. parvus Zone. These data document a corresponding negative shift of δ13Corg and δ13Ccarb, values and low TOC contents with the onset of growth of calcified microbial framestones (a postextinction ‘disaster facies’) immediately below the base of the Griesbachian H. parvus Zone. Based on paleontological evidence, the first occurrence of the ‘disaster facies’ follows the extinction event, which implies that the 13C-depleted values above this facies postdate the event. This suggests that two separate events had to account for the initiation of the extinction and the δ13C excursion. However, the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of Early Triassic ecosystems. Based on data from PTB sections worldwide of a greater δ13C offset in high compared with low latitudes, we propose that methane eruptions from thermal destabilization of high-latitude clathrate deposits may have led to the negative δ13C shift and may have caused long-term adverse ecological conditions.

δ13C and δ15N profiles in 14C-dated Oxisol and Vertisols as a function of soil chemistry and mineralogy

The analyses of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of soil organic matter (SOM) is an increasingly used tool to estimate soil carbon turnover, to assess degree of soil development, and to study historical C3/C4 vegetation changes. However, the exact processes that control 13C- and 15N-enrichment of SOM within a soil profile are still not clearly identified. To better understand the isotopic processes associated with decomposition of SOM, we studied two Vertisol profiles and one Oxisol profile from southern Queensland by radiogenic (14C), stable isotopic (δ13C, δ15N), and spectroscopic (13C-NMR and FTIR) methods. The findings of this study demonstrate that fundamental differences exist in δ13C and δ15N fractionation dynamics in different soil types and that isotopic fractionation is highly influenced by soil chemistry, mineralogy, and type of organic matter input. Stable isotopic analyses of the Oxisol show the typically observed increase in δ13C and δ15N in the subsurface horizon whereas the Vertisols show consistently decreasing values with depth. The high degree of 13C-enrichment in the Oxisol compared with the Vertisols cannot be simply explained with increased fractionation due to soil age, as the 14C age of the Vertisols is greater and increases more rapidly with depth, compared with that of the Oxisol. Data from 13C-NMR, XRF and IR data together with data on pH and clay content reveal a more complex picture of isotopic fractionation in soils. The Oxisol is dominated by O-alkyl carbon and aromatic material whereas the Vertisols contain higher amounts of alkyl carbon. Smectite and kaolinite are the dominant clay minerals in the Vertisols while the Oxisol is dominated by gibbsite, kaolinite, and Fe and Al-oxides. We suggest that the 13C- and 15N-depletion in the Vertisols is associated with low pH, which inhibits nitrification and promotes stabilization of 13C-depleted alkyl material by smectitic clays. The 13C-enrichment in the Oxisol correlates with a high abundance of relatively 13C-enriched O-alkyl carbon, which is a mix of primary materials (plant carbohydrates) as well as secondary (microbially synthesized) carbon. The abundance of relatively labile O-alkyl carbon even at depth is likely due to physico-chemical protection through complexation with Fe- and Al-oxides.

Search for evidence of impact at the Permian-Triassic boundary in Antarctica and Australia

Life on Earth was almost destroyed some 250 m.y. ago in the most profound of all known mass extinction events. We investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias, search for shocked quartz, and analysis for iridium in Permian-Triassic boundary sections at Graphite Peak and Mount Crean, Antarctica, and Wybung Head, Australia. Thin claystone breccias at the isotopically and paleobotanically defined boundary at all three locations are interpreted as redeposited soil rather than impact ejecta. The breccias at all three locations also yielded shocked quartz, but it is an order of magnitude less abundant (0.2 vol%) and smaller (only as much as 176 micrometers m diameter) than shocked quartz at some Cretaceous-Tertiary boundary sites. Faint iridium “anomalies” were detected (up to 134 pgṁg −1 ). These values are an order of magnitude less than iridium anomalies at some Cretaceous-Tertiary boundary sites. Furthermore, peak iridium values are as much as 1 m below the isotopically and paleobotanically defined boundary. The idea that impact caused the extinctions thus remains to be demonstrated convincingly.

Microbial utilisation Of biochar-derived carbon

Whilst largely considered an inert material, biochar has been documented to contain a small yet significant fraction of microbially available labile organic carbon (C). Biochar addition to soil has also been reported to alter soil microbial community structure, and to both stimulate and retard the decomposition of native soil organic matter (SOM). We conducted a short-term incubation experiment using two (13)C-labelled biochars produced from wheat or eucalypt shoots, which were incorporated in an aridic arenosol to examine the fate of the labile fraction of biochar-C through the microbial community. This was achieved using compound specific isotopic analysis (CSIA) of phospholipid fatty acids (PLFAs). A proportion of the biologically-available fraction of both biochars was rapidly (within three days) utilised by gram positive bacteria. There was a sharp peak in CO2 evolution shortly after biochar addition, resulting from rapid turnover of labile C components in biochars and through positive priming of native SOM. Our results demonstrate that this CO2 evolution was at least partially microbially mediated, and that biochar application to soil can cause significant and rapid changes in the soil microbial community; likely due to addition of labile C and increases in soil pH.

Effect of banded biochar on dryland wheat production and fertiliser use in south-western Australia: an agronomic and economic perspective

Effects of banded biochar application on dryland wheat production and fertiliser use in 4 experiments in Western Australia and South Australia suggest that biochar has the potential to reduce fertiliser requirement while crop productivity is maintained, and biochar additions can increase crop yields at lower rates of fertiliser use. Banding was used to minimise wind erosion risk and place biochar close to crop roots. The biochars/metallurgical chars used in this study were made at relatively high temperatures from woody materials, forming stable, low-nutrient chars. The results suggest that a low biochar application rate (~1 t/ha) by banding may provide significant positive effects on yield and fertiliser requirement. Benefits are likely to result from improved crop nutrient and water uptake and crop water supply from increased arbuscular mycorrhizal fungal colonisation during dry seasons and in low P soils, rather than through direct nutrient or water supply from biochars. Financial analysis using farm cash flow over 12 years suggests that a break-even total cost of initial biochar use can range from AU

Marked changes in herbicide sorption–desorption upon ageing of biochars in soil

40 to 190/ha if the benefits decline linearly to nil over 12 years, taking into account a P fertiliser saving of 50% or a yield increase of 10%, or both, assuming long-term soil fertility is not compromised. Accreditation of biochar for carbon trading may assist cost reduction.