Bhupinder Pal Singh

Characterisation and evaluation of biochars for their application as a soil amendment

Biochar properties can be significantly influenced by feedstock source and pyrolysis conditions; this warrants detailed characterisation of biochars for their application to improve soil fertility and sequester carbon. We characterised 11 biochars, made from 5 feedstocks [Eucalyptus saligna wood (at 400°C and 550°C both with and without steam activation); E. saligna leaves (at 400°C and 550°C with activation); papermill sludge (at 550°C with activation); poultry litter and cow manure (each at 400°C without activation and at 550°C with activation)] using standard or modified soil chemical procedures. Biochar pH values varied from near neutral to highly alkaline. In general, wood biochars had higher total C, lower ash content, lower total N, P, K, S, Ca, Mg, Al, Na, and Cu contents, and lower potential cation exchange capacity (CEC) and exchangeable cations than the manure-based biochars, and the leaf biochars were generally in-between. Papermill sludge biochar had the highest total and exchangeable Ca, CaCO3 equivalence, total Cu, and potential CEC, and the lowest total and exchangeable K. Water-soluble salts were higher in the manure-based biochars, followed by leaf, papermill sludge, and wood biochars. Total As, Cd, Pb, and polycyclic aromatic hydrocarbons in the biochars were either very low or below detection limits. In general, increase in pyrolysis temperature increased the ash content, pH, and surface basicity and decreased surface acidity. The activation treatment had a little effect on most of the biochar properties. X-ray diffraction analysis showed the presence of whewellite in E. saligna biochars produced at 400°C, and the whewellite was converted to calcite in biochars formed at 550°C. Papermill sludge biochar contained the largest amount of calcite. Water-soluble salts and calcite interfered with surface charge measurements and should be removed before the surface charge measurements of biochar. The biochars used in the study ranged from C-rich to nutrient-rich to lime-rich soil amendment, and these properties could be optimised through feedstock formulation and pyrolysis temperature for tailored soil application.

Biochar carbon stability in a clayey soil as a function of feedstock and pyrolysis temperature.

The stability of biochar carbon (C) is the major determinant of its value for long-term C sequestration in soil. A long-term (5 year) laboratory experiment was conducted under controlled conditions using 11 biochars made from five C3 biomass feedstocks (Eucalyptus saligna wood and leaves, papermill sludge, poultry litter, cow manure) at 400 and/or 550 °C. The biochars were incubated in a vertisol containing organic C from a predominantly C4-vegetation source, and total CO(2)-C and associated δ(13)C were periodically measured. Between 0.5% and 8.9% of the biochar C was mineralized over 5 years. The C in manure-based biochars mineralized faster than that in plant-based biochars, and C in 400 °C biochars mineralized faster than that in corresponding 550 °C biochars. The estimated mean residence time (MRT) of C in biochars varied between 90 and 1600 years. These are conservative estimates because they represent MRT of relatively labile and intermediate-stability biochar C components. Furthermore, biochar C MRT is likely to be higher under field conditions of lower moisture, lower temperatures or nutrient availability constraints. Strong relationships of biochar C stability with the initial proportion of nonaromatic C and degree of aromatic C condensation in biochar support the use of these properties to predict biochar C stability in soil.

Interactive priming of biochar and labile organic matter mineralization in a smectite-rich soil.

Biochar is considered as an attractive tool for long-term carbon (C) storage in soil. However, there is limited knowledge about the effect of labile organic matter (LOM) on biochar-C mineralization in soil or the vice versa. An incubation experiment (20 °C) was conducted for 120 days to quantify the interactive priming effects of biochar-C and LOM-C mineralization in a smectitic clayey soil. Sugar cane residue (source of LOM) at a rate of 0, 1, 2, and 4% (w/w) in combination with two wood biochars (450 and 550 °C) at a rate of 2% (w/w) were applied to the soil. The use of biochars (~ -36‰) and LOM (-12.7‰) or soil (-14.3‰) with isotopically distinct δ(13)C values allowed the quantification of C mineralized from biochar and LOM/soil. A small fraction (0.4-1.1%) of the applied biochar-C was mineralized, and the mineralization of biochar-C increased significantly with increasing application rates of LOM, especially during the early stages of incubation. Concurrently, biochar application reduced the mineralization of LOM-C, and the magnitude of this effect increased with increasing rate of LOM addition. Over time, the interactive priming of biochar-C and LOM-C mineralization was stabilized. Biochar application possesses a considerable merit for long-term soil C-sequestration, and it has a stabilizing effect on LOM in soil.

Influence of biochar application to soil on the availability of As, Cd, Cu, Pb, and Zn to maize (Zea mays L.).

Biochar has gained importance due to its ability to increase the long-term soil carbon pool and improve crop productivity. However, little research has been done to evaluate the influence of biochar application to soil on the bioavailability of trace elements to plants. A pot experiment was conducted to investigate the influence of biochar on the availability of As, Cd, Cu, Pb, and Zn to maize (Zea mays L.). An activated wood biochar, pyrolysed at 550°C, was applied at 3 rates (0, 5, and 15 g/kg) in factorial combinations with 3 rates (0, 10, and 50 mg/kg) each of As, Cd, Cu, Pb, and Zn separately to a sandy soil. After 10 weeks of growth, plants were harvested, shoot dry matter yield was measured, and concentration of trace elements in shoots was analysed. The soil in pots was analysed for extractable trace elements. The results showed that the addition of wood biochar to soil did not have any significant effect on the dry matter yield of maize plants, even at the highest rate of application. However, trace element application significantly reduced the dry matter yield from 10 to 93% depending on the type of trace element. Biochar application decreased the concentration of As, Cd, and Cu in maize shoots, especially at the highest rate of trace element application, whereas the effects were inconsistent on Pb and Zn concentrations in the shoots. The concentrations of extractable As and Zn in soil increased with biochar application, whereas extractable Cu did not change, Pb decreased, and Cd showed an inconsistent trend. Sorption of trace elements on biochar with initial loadings up to 200 µmol at pH 7 occurred in the order: Pb > Cu > Cd > Zn > As. The results show that biochar application can significantly reduce the availability of trace elements to plants and suggest that biochar application may have potential for the management of soils contaminated by trace elements.

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.

Challenges and opportunities for mitigating nitrous oxide emissions from fertilized cropping systems

Nitrous oxide (N2O) is often the largest single component of the greenhouse-gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O-producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Long-term influence of biochar on native organic carbon mineralisation in a low-carbon clayey soil

Biochar can influence native soil organic carbon (SOC) mineralisation through “priming effects”. However, the long-term direction, persistence and extent of SOC priming by biochar remain uncertain. Using natural 13C abundance and under controlled laboratory conditions, we show that biochar-stimulated SOC mineralisation (“positive priming”) caused a loss of 4 to 44 mg C g−1 SOC over 2.3 years in a clayey, unplanted soil (0.42% OC). Positive priming was greater for manure-based or 400°C biochars, cf. plant-based or 550°C biochars, but was trivial relative to recalcitrant C in biochar. From 2.3 to 5.0 years, the amount of positively-primed soil CO2-C in the biochar treatments decreased by 4 to 7 mg C g−1 SOC. We conclude that biochar stimulates native SOC mineralisation in the low-C clayey soil but that this effect decreases with time, possibly due to depletion of labile SOC from initial positive priming, and/or stabilisation of SOC caused by biochar-induced organo-mineral interactions.

Soil Health Indicators Under Climate Change: A Review of Current Knowledge

Soil health indicators are a composite set of measurable physical, chemical and biological attributes which relate to functional soil processes and can be used to evaluate soil health status, as affected by management and climate change. Major soil health indicators discussed in the context of climate change are: aggregate stability, water infiltration, and bulk density, soil organic matter content, carbon and nitrogen cycling, microbial biomass and activity, and microbial diversity. In this chapter, we highlight that the selection of a suite of soil health indicators within a minimum data set depends on their sensitivity to management changes, and capacity to integrate and relate to important soil functions. These soil health indicators must also be sensitive to drivers of global change (increasing temperatures, elevated atmospheric carbon dioxide and atmospheric nitrogen deposition, increasing variability in amount, intensity, and distribution of precipitation, extreme climatic events, and their interactions) and should be able to indicate the mitigation and adaptive capability of soil and its resilience to climate change, and provide early warning for the need of implementing climate adaptive management strategies.

Soil health and climate change

Soil health indicators for the climate change.- Soil attributes and soil processes in response to the climate change.- Conventional land use systems.- Organic farming, biochar and bioenergy systems.

In Situ Persistence and Migration of Biochar Carbon and Its Impact on Native Carbon Emission in Contrasting Soils under Managed Temperate Pastures

Pyrogenic carbon (PyC) is an important component of the global soil carbon (C) pool, but its fate, persistence, and loss dynamics in contrasting soils and environments under planted field conditions are poorly understood. To fill this knowledge gap, a 13C-labelled biochar, as a surrogate material for PyC, produced from Eucalyptus saligna by slow pyrolysis (450°C; δ13C -36.7‰) was surface (0−10 cm) applied in C3 dominated temperate pasture systems across Arenosol, Cambisol and Ferralsol. The results show a low proportion of the applied biochar-C mineralised over 12 months in a relatively clay- and C-poor Arenosol (i.e., 2.0% loss via mineralisation), followed by a clay- and C-rich Cambisol (4.6%), and clay-, C- and earthworm-rich Ferralsol (7.0%). The biochar-C mean residence time (MRT), estimated by different models, varied between 44−1079 (Arenosol), 18−172 (Cambisol), and 11−29 (Ferralsol) years, with the shorter MRT estimated by a one-pool exponential and the longer MRT by an infinite-pool power or a two-pool exponential model. The two-pool model was best fitted to biochar-C mineralisation. The biochar-C recovery in the 12−30 cm soil layer varied from between 1.2% (Arenosol), 2.5−2.7% (Cambisol) and 13.8−15.7% (Ferralsol) of the applied biochar-C after 8−12 months. There was a further migration of biochar-C below the 50-cm depth in the Arenosol, as the combined biochar-C recovery in the mineralised pool and soil profile (up to 30 or 50 cm) was 82%, in contrast to 101% in the Cambisol and 104% in the Ferralsol after 12 months. These results indicate that the downward migration of biochar-C was greatest in the Arenosol (cf. Cambisol and Ferralsol). Cumulative CO2-C emission from native soil-plant sources was lower (p <0.10) in the biochar-amended vs. non-amended Ferralsol. This field-based study shows that the downward migration of biochar-C exceeded its loss via mineralisation in the Arenosol and Ferralsol, but not in the Cambisol. It is thus important to understand biochar-soil interactions to maximise long-term biochar C sequestration potential in planted soil systems.