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The implications for greenhouse gas emissions of optimizing a slow pyrolysis-based bioenergy system for biochar and energy production rather than solely for energy production were assessed. Scenarios for feedstock production were examined using a life-cycle approach. We considered both purpose grown bioenergy crops (BEC) and the use of crop wastes (CW) as feedstocks. The BEC scenarios involved a change from growing winter wheat to purpose grown miscanthus, switchgrass, and corn as bioenergy crops. The CW scenarios consider both corn stover and winter wheat straw as feedstocks. Our findings show that the avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land (2--19 Mg CO2 ha(-1) y(-1)) than used solely for fossil energy offsets. 41--64% of these emission reductions are related to the retention of C in biochar, the rest to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions other than CO2. Despite a reduction in energy output of approximately 30% where the slow pyrolysis technology is optimized to produce biochar for land application, the energy produced per unit energy input at 2--7 MJ/MJ is greater than that of comparable technologies such as ethanol from corn. The C emissions per MWh of electricity production range from 91-360 kg CO2 MWh(-1), before accounting for C offset due to the use of biochar are considerably below the lifecycle emissions associated with fossil fuel use for electricity generation (600-900 kg CO2 MWh(-1)). Low-temperature slow pyrolysis offers an energetically efficient strategy for bioenergy production, and the land application of biochar reduces greenhouse emissions to a greater extent than when the biochar is used to offset fossil fuel emissions.

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is pro- posed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver im- mediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (

Current models of soil organic matter (SOM) turnover tend to invoke pools that are defined by their contrasting first-order reactivity constants but which cannot be directly measured. New models may be based around fractions defined by procedures that can be used to isolate them experimentally. The drawback of such fractions is that they may display properties that are not sufficiently distinct or which vary in time or space. In this study the properties of two fractions from soils of contrasting geographical origin and under different nutrient management were examined using 13 C nuclear magnetic resonance (NMR) spectroscopy. The fractions were free SOM (FR-SOM, discrete organic particles located between stable aggregates), and intra-aggregate SOM (IA-SOM, discrete organic particles within stable aggregates). The composition of both fractions was highly consistent across soil types and environments, but the fractions differed significantly in the proportion of C present in five of the seven functional C groups identified by NMR (P

We used thermal analysis to compare the proportions of active and more stable components in soil organic matter (SOM) fractions and whole soil under contrasting agricultural land-uses. The fractions (free light, intra-aggregate, and organomineral fractions) were isolated using density fractionation. Exothermic weight loss between 300 and 350°C was attributed to a relatively labile portion comprising carboxyl and aliphatic C, and that between 400 and 450°C to the decomposition of material rich in aromatic components. Under arable cultivation, free light SOM showed much greater weight loss in the first exothermic range than intra-aggregate SOM. In soil receiving very small inputs of organic matter (a long-term bare fallow) the free light and intra-aggregate fractions displayed similar characteristics and resembled the intra-aggregate fraction from the arable soil. The difference between the free light and intra-aggregate fractions was also small for the grassland soil but the fractions resembled the free light fraction from the arable soil. Small total weight loss for whole soil and organomineral fractions demonstrated the value of physical fractionation techniques in establishing the effect of land-use on SOM with greater precision than is possible whole (unfractionated) soil.

A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for measuring microbial biomass C (CBIO) and N (NBIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots or changing soil water content (0.44–0.55 kg kg–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both CBIO and NBIO (P

The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding.

Methane production in soil is a microbiological process that occurs under strict anaerobic conditions. A laboratory incubation study was conducted using 10 wetland rice (Oryza sativa L.) soils from the Philippines to establish soil characteristics that govern the redox characteristics and CH 4 production of soils upon wetting. Labile soil organic matter in the Ap horizon was quantified as enrichment of C and N and non-clay-protected C and N fractions. The C/N ratio of the enriched fraction controlled the rate of reduction upon flooding, whereas the buffering capacity, measured as extractable Fe 3+ content, controlled the reduction capacity for the soils. Methane production was influenced both by the reduction characteristics of the soils and labile organic substrates.

Black carbon (BC) is an important fraction of many soils worldwide and plays an important role in global C biogeochemistry. However, few studies have examined how it influences the mineralization of added organic matter (AOM) and its incorporation into soil physical fractions and whether BC decomposition is increased by AOM. BC-rich Anthrosols and BC-poor adjacent soils from the Central Amazon (Brazil) were incubated for 532 days either with or without addition of 13 C-isotopically different plant residue. Total C mineralization from the BC-rich Anthrosols with AOM was 25.5% ( P P P P 13 C-enriched microbial culture. The recovery was found to be 21–41% lower ( P

A laboratory study was conducted to compare methods of labelling the soil NH4+ pool with 15N as a prerequisite to the measurement of gross N mineralisation. Composite soil (0–12 cm) was collected from 12 sites differing in land use and soil texture. Three methods were used to apply 15N to the soil: (i) addition of a 15NH3–air gas mixture to the headspace above the soil (gas jar), (ii) injection of a 15NH3–air gas mixture into re-packed soil cores (gas injector) and (iii) addition of a (15NH4)2SO4 solution pipetted onto the soil surface (solution). 15N isotopic dilution was determined between 24 and 72 h after 15N application. Of the applied 15N 52 to 93% was recovered as inorganic N 24 h after application. Less 15N was recovered in the clay loam compared to the sandy loam and silty clay loam for all methods. Recovery from the gas injector was lower than from the gas jar or solution treatments in the sandy loam and silty clay loam. No difference in the recovery of applied 15N between methods was observed in the clay loam. 15N isotopic dilution was less in the gas jar compared to the gas injector and solution treatments. This resulted in significantly lower estimates of gross N mineralisation rates and NH4+ consumption for the gas jar treatment. The non-uniform distribution of 15N through the soil probably caused these differences as a consequence of 15NH3 dissolving quickly in the surface of the soil. In seven of the 12 soils, gross rates of N mineralisation were not significantly different when 15N was applied as solution or by gas injection. In the remaining five soils, estimates of gross N mineralisation rates were greater in the solution treatment. Ammonium consumption was significantly different between the solution and gas injector treatments in three soils. Where there were differences in values for gross N mineralisation and NH4+ consumption rates between methods, the effects were not associated with a particular soil texture or land use. Greater nitrification of 15NH4+ to 15NO3− and shorter pseudo-residence times of the NH4+ pool were observed in the solution treatment compared to gas injector. This suggests a difference in the distribution of 15N within soil microsites, with the 15N applied in the solution treatment being more accessible for microbial consumption. Nevertheless, application of 15N as an NH4+ solution, or injection of 15NH3 gas into soil, resulted in estimates of a similar magnitude for gross N mineralisation rates and identified the same differences between soil type and land use.