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Methane (CH4) is the second greatest contributor to anthropogenic climate change. Emissions have tripled since preindustrial times and continue to rise rapidly, given the fact that the key sources of food production, energy generation and waste management, are inexorably tied to population growth. Until recently, the pursuit of CH4 mitigation approaches has tended to align with opportunities for easy energy recovery through gas capture and flaring. Consequently, effective abatement has been largely restricted to confined high-concentration sources such as landfills and anaerobic digesters, which do not represent a major share of CH4’s emission profile. However, in more recent years we have witnessed a quantum leap in the sophistication, diversity and affordability of CH4 mitigation technologies on the back of rapid advances in molecular analytical techniques, developments in material sciences and increasingly efficient engineering processes. Here, we present some of the latest concepts, designs and applic...

In developing countries, the simple biogas digesters installed underground without heating or stirring are seen as a 'green' technology to convert animal waste into biogas, a source of bio-energy. However, quantitative estimates of biogas production of manures from steers fed local feed diets at actual incubation temperatures have yet to be carried out. The aim of this study was to determine the methane (CH4) production potential of manures from steers in Vietnam offered traditional feed rations or supplemental diets. Biochemical CH4 production (BMP) was measured in batch tests at 30°C using manures collected from two different experiments of steers fed diets containing feed supplements. BMP was 110.1 (NLkg-1 VS) for manure from steers receiving a control diet, significantly lower 79.0 (NL kg-1 VS) for manure from steers fed a diet containing 0.3% tannin (%DM), but then showed an increasing trend to 90.9 and 91.2 (NL kg-1 VS) for manures from steers receiving 0.4 and 0.5% tannin (%DM) supplements, respectively. Similarly, the CH4 production (NL kg-1 VS) of manure from steers was 174 for control, 142 for control supplemented concentrate (C), 143 for control added rice straw treated with urea (R), and 127 for control supplemented C and R. Our results show there was a decrease in CH4 emissions from steer manures through using supplemented rations.

Mitigating methane (CH) emissions from New Zealand dairy effluent ponds using volcanic pumice soil biofilters has been found to be a promising technology. Because the soil column biofilter prototype previously used was cumbersome, here we assess the effectiveness of volcanic pumice soil-perlite biofilter media in a floating system to remove high concentrations of CH emitted from a dairy effluent pond and simultaneously in a laboratory setting. We measured the CH removal over a period of 11 mo and determined methanotroph population dynamics using molecular techniques to understand the role of methanotroph population abundance and diversity in CH removal. Irrespective of the season, the pond-floating biofilters removed 66.7 ± 5.7% CH throughout the study period and removed up to 101.5 g CH m h. By contrast, the laboratory-based floating biofilters experienced more biological disturbances, with both low (∼34%) and high (∼99%) CH removal phases during the study period and an average of 58% of the CH oxidized. These disturbances could be attributed to the measured lower abundance of type II methanotroph population compared with the pond biofilters. Despite the acidity of the pond biofilters increasing significantly by the end of the study period, the biofilter encouraged the growth of both type I ( and ) and type II ( and ) methanotrophs. This study demonstrated the potential of the floating biofilters to mitigate dairy effluent ponds emissions efficiently and indicated methanotroph abundance as a key factor controlling CH oxidation in the biofilter.

We have followed the responses of the properties of a sandy soil (0–50 mm), including carbon (C) and nitrogen (N) concentrations, to 10 years of ambient and elevated (475 μl l −1 ) CO 2 in a FACE (Free Air CO 2 Enrichment) experiment in a grazed pasture in North Island, New Zealand. We have previously reported results for the first 5 years where, at this relatively low level of CO 2 enrichment, most soil properties changed gradually and non-significantly. Here we add data from a further 5 years of enrichment and find that most soil properties had changed significantly. Soil moisture was greater under elevated CO 2 but we could find no evidence that this was the cause of changes in other properties, suggesting that increased inputs of C and N in the high CO 2 regime were driving soil differences. When soil total C and N were adjusted to account for differences in starting concentrations there was evidence of increased pool sizes and increased C/N under elevated CO 2 . Microbial C and N pools also increased with CO 2 as did heterotrophic respiration and labile C and N fractions. There were few changes in N mineralization but no evidence for reduced rates under elevated CO 2 . There was little evidence for a direct effect of changes in soil properties on plant biomass responses to CO 2 but the changes we observed relate to pools and fluxes that are known to be important in both production and environmental outcomes in grassland systems.

We describe experiments to better understand how CH 4 oxidation rates by different methanotroph communities respond to changing CH 4 concentrations. We used a novel system of automatically monitored chambers to investigate the response of CH 4 oxidation rates in a New Zealand pasture and adjacent pine forest soil exposed to varying atmospheric CH 4 concentrations. Type II methanotrophs that dominate CH 4 oxidation in the forest soil became progressively saturated as CH 4 concentrations rose from ambient (1.8 ppmv) to 570 ppmv, as shown by a decrease in uptake efficiency from 20% to 2% removal. By contrast, CH 4 oxidation in the pasture soil where Type I methanotrophs dominate increased in proportion to the increase in CH 4 inlet concentration, oxidising about 2% of the inlet CH 4 flux throughout. Modelling based on Michaelis-Menten kinetics revealed that low-affinity (Type I) methanotrophs were solely responsible for CH 4 oxidation in pasture soils, whereas high affinity (Type II) methanotrophs only contributed about 10% of the CH 4 oxidation in the forest soil. Increased aeration status using a soil–perlite (1:1) mixture doubled CH 4 oxidation rates at both ambient (1.8 ppmv) and 40 ppmv atmospheric CH 4 . A similar volcanic soil previously exposed for 8 y to high CH 4 fluxes from a landfill had removal efficiencies consistently above 95% for atmospheric CH 4 concentrations up to 7500 ppmv when the CH 4 oxidation rate was7000 μg CH 4 kg −1 soil h −1 .

Dairy farm effluent ponds are a source of methane (CH 4 ), a potent greenhouse gas. Biofiltration, whereby CH 4 is oxidised by methanotrophic bacteria, is a potentially cost-effective CH 4 mitigation technology. We report on the performance of a field-scale biofilter treating dairy farm effluent pond CH 4 emissions for 16 months. This study is the first to report on the feasibility of using biofiltration to mitigate dairy waste CH 4 emissions. The 70-L filter comprised a 1:1 volumetric mixture of volcanic soil from a landfill and perlite. Biogas collected in a floating cover on a 4-m 2 section of the pond was directed through the biofilter's base. Air was pumped through the filter to supply oxygen to the methanotrophs. The filter's maximum CH 4 removal rate was 16 g m −3 h −1 (or 53 μg g −1 h −1 ), which is high compared with literature landfill soil oxidation rates (typically −1 h −1 ). At the trial's conclusion, the filter experienced acid accumulation, due to oxidation of H 2 S in the inlet biogas (evidenced by low pH [3.9] and high sulphate-S [1079 mg −1 kg −1 ] at the base of the filter compared with the top [pH = 4.6, sulphate-S = 369 mg −1 kg −1 ]). Nonetheless, the filter's oxidation rate peaked at the end of the experiment indicating negligible H 2 S impact on overall performance over the 16-month period. The results showed that a 50-m 3 filter would be needed to offset CH 4 emissions (approximately 720 g h −1 ) from a typical 1000-m 2 dairy effluent pond. As this calculation is based on the efficiency of a single experimental filter, field testing of replicate biofilters is needed to accurately establish full-scale filter sizing. Nonetheless, this study has shown that biofilter technology is feasible to mitigate dairy effluent pond CH 4 emissions. Current research is underway to make the filter more economically viable through design optimisation.

Soil methane (CH(4)) biofilters, containing CH(4)-oxidizing bacteria (methanotrophs), are a promising technology for mitigating greenhouse gas emissions. However, little is known about long-term biofilter performance. In this study, volcanic pumice topsoils (0-10 cm) and subsoils (10-50 cm) were tested for their ability to oxidize a range of CH(4) fluxes over 1 yr. The soils were sampled from an 8-yr-old and a 2-yr-old grassed landfill cover and from a nearby undisturbed pasture away from the influence of CH(4) generated by the decomposing refuse. Methane was passed through the soils in laboratory chambers with fluxes ranging from 0.5 g to 24 g CH(4) m(-3) h(-1). All topsoils efficiently oxidized CH(4). The undisturbed pasture topsoil exhibited the highest removal efficiency (24 g CH(4) m(-3) h(-1)), indicating rapid activation of the methanotroph population to the high CH(4) fluxes. The subsoils were less efficient at oxidizing CH(4) than the topsoils, achieving a maximum rate oxidation rate of 7 g CH(4) m(-3) h(-1). The topsoils exhibited higher porosities; moisture contents; surface areas; and total C, N, and available-P concentrations than the subsoils, suggesting that these characteristics strongly influence growth and activity of the CH(4)-oxidizing bacteria. Soil pH values and available-P levels gradually declined during the trial, indicating a need to monitor chemical parameters closely so that adjustments can be made when necessary. However, other key soil physicochemical parameters (moisture, total C, total N) increased over the course of the trial. This study showed that the selected topsoils were capable of continually sustaining high CH(4) removal rates over 1 yr, which is encouraging for the development of biofilters as a low-maintenance greenhouse gas mitigation technology.

In forest ecosystems, few data are available on transfer rates of litterfall carbon (C) to mineral soil. Such data are, nevertheless, needed for predicting the effects of forest land-use change and management on soil C stocks. We here report the transfer of C from Pinus radiata litter to mineral soil over 117 weeks, using 14 C-labelled needles mixed with unlabelled needles in lysimeters placed on the forest floor of a 5-year-old P. radiata stand. Mean annual temperature was about 12.9°C and mean annual rainfall about 995 mm; the soil was a well-drained silt loam. Measurements were made at 39, 78 and 117 weeks of 14 C in residual litter and in 10-mm increments of mineral soil to 50 mm depth and 25-mm increments from 50 to 100 mm depth. Measurements were also made of 14 C-CO 2 production, at frequent intervals over the first 5 weeks and then less frequently. Recovery of 14 C in litter and mineral soil ranged from 51 to 66% at the different exposure times. Cumulative respired 14 C-CO 2 , expressed as a percentage of the initially added 14 C, increased from 16 to 19% after exposure times of 39 and 117 weeks, respectively. Total recovery of the added 14 C did not differ significantly (P > 0.12) with time over the three measurement periods, with means ranging from 68 to 84%. Apparent losses of 14 C were associated with large replicate variability, with coefficients of variation ranging from 20 to 31 %, and with some disturbance of litter in the lysimeters by birds. We estimate that 1.0-2.2% of the litter 14 C was transferred annually to 10-100-mm depth of mineral soil. On the basis of microbial biomass- 14 C measurements, this transferred C contained proportionately more microbial (labile) C than did the older total C in mineral soil. Results therefore are consistent with other studies on forests with well-developed organic horizons indicating that C in humified organic matter, rather than in newly fallen litter, is the main above-ground source for transfer of C to the mineral soil.

Soil has been identified as a possible carbon (C) sink to mitigate increasing atmospheric CO2 concentration. However, several recent studies have suggested that the potential of soil to sequester C is limited and that soil may become saturated with C under increasing CO2 levels. To test this concept of soil C saturation, we studied a gley and organic soil at a grassland site near a natural CO2 spring. Total and aggregate-associated soil organic C (SOC) concentration showed a significant increase with atmospheric CO2 concentration. An asymptotic function showed a better fit of SOC and aggregation with CO2 level than a linear model. There was a shift in allocation of total C from smaller size fractions to the largest aggregate fraction with increasing CO2 concentration. Litter inputs appeared to be positively related to CO2 concentration. Based on modeled function parameters and the observed shift in the allocation of the soil C from small to large aggregate-size classes, we postulate that there is a hierarchy in C saturation across different SOC pools. We conclude that the asymptotic response of SOC concentration at higher CO2 levels indicates saturation of soil C pools, likely because of a limit to physical protection of SOC.

Forest harvest results in the removal of a large reservoir of terrestrial carbon with potential significant effects on net CO 2 emissions, but concomitant effects on other atmospheric trace gas fluxes are poorly understood. We measured CO 2 , CH 4 and N 2 O fluxes between soils and the atmosphere over 3 years at a recently harvested site under Pinus radiata on a volcanic soil of high-fertility status using replicated, large, in situ chambers to enclose three harvest residue treatments. Temporal changes in CO 2 and N 2 O emissions were also measured over a wider harvested area using small chambers. The residue (slash) treatments were a control (‘no-slash’), ‘normal-slash’ typical of the site and ‘high-slash’ (three times normal-slash). Mass loss was inversely related to all size categories of slash, and averaged 98% for litter and 34% for large wood (76–120 mm diameter). C:N ratios generally declined as a result of increased N concentrations. Overall, CO 2 -C production was significantly higher ( P = 0.02) in the ‘normal-slash’ (by 27%) and ‘high-slash’ (by 72%) than in the ‘no-slash’ treatments. An interaction between treatment and time explained ( P = 0.05) the CO 2 -C flux data better than did the interaction between treatment and soil moisture ( P = 0.07). Evidence from small-chamber CO 2 -C flux data collected over a wider area before and after harvest suggested little apparent effect of soil disturbance during harvest. Averaged over 3 years, the annual CO 2 -C efflux from the large chambers was 8.3 ± 1.1 Mg ha −1 . Methane uptake was apparently depressed by surface soil disturbance during harvest, because it increased after harvest by 70% in the ‘normal-slash’ and ‘high-slash’ treatments to average 12 ± 1 kg CH 4 ha −1 year −1 . Neither NH 4 + nor NO 3 − -N concentrations had any measurable effect on CH 4 uptake. Despite the high N fertility of the harvest site, N 2 O emissions were low overall (0.56 ± 0.17 kg N 2 O-N ha −1 year −1 ) and differed little between treatments, apart from a spike shortly after harvest. Overall, during the time frame of the first commitment period under the Kyoto Protocol, the three greenhouse gases (CO 2 , CH 4 and N 2 O) contributed 87, −1 and 14%, respectively, to combined emissions on a CO 2 -equivalent basis from this fertile harvest site.

Rising concentrations of atmospheric [CO2] in a multi-species ecosystem can influence species composition and increase plant productivity, but have a less predictable effect on soil C storage and nutrient availability. Using a free-air [CO2]-enriched (FACE) system and seasonal sampling over a 5-year period, we examined the influence of elevated atmospheric [CO2] (475 μL L−1) on soil C and N pools and mineralization in a fertilized (P, K, S), sheep-grazed pasture of mixed grass, clover, and forb species on a seasonally dry sand (Mollic Psammaquent). Annual yields of herbage dry matter ranged from about 300 to 1600 g m−2. Total yields did not increase significantly under elevated [CO2], but the proportions of clovers and forbs increased markedly. Most properties in 0–50 mm-depth soil differed significantly (P 0.10) for moisture, pH, total C and N, extractable C and organic N, microbial C, and mineral-N. However, microbial N, CO2-C production (0–14 days) in field-moist soil, and net mineral-N production (14–56 days) in soil at 60% of water-holding capacity were significantly higher (per unit weight of soil) in the elevated-[CO2] treatment (P=0.071, 0.063, 0.003, respectively); the degree of these treatment differences was roughly similar when values were also expressed on a total C or N basis. Relationships with soil moisture were mainly non-significant for microbial C and N, but mainly significant (P

Both CO 2 –C production and the decomposability of grass leaf litter in a gley soil from a naturally occurring CO 2 spring were previously shown to be influenced by the atmospheric CO 2 concentrations under which the soil and litter were sampled. Here we investigate C mineralization in an organic soil from very high CO 2 environments (range 1220–3900 μl l −1 ) at the same spring, and the effect of added leaf litter on CO 2 –C production. Carbon mineralization in the organic soil was unusual in two respects: (1) the proportion of labile components was very high, with more than 11% of the initial soil C being metabolized to CO 2 –C after 56 d at 25 °C; (2) rates of CO 2 –C production in autumn samples increased on incubation, after an initial decline. Decomposition was initially more rapid in C3 Holcus lanatus (Yorkshire fog) than in C4 Pennisetum clandestinum (kikuyu) litter, but differed little in samples from different atmospheric CO 2 concentrations. Overall, the effects of environmental variables on estimates of litter decomposability in the organic soil were similar to, although much less marked than, those in the gley soil. Results suggest that organic components in the organic soil were metabolized at least as readily as those of added litter during the later stages of the 56-d incubation.

Summary Methane emissions from ruminant livestock are responsible for 45 % of New Zealand’s combined CO2-equivalent greenhouse gas inventory, and arise principally from sheep. Using a flock of 6-month old sheep (20 ha–1) grazing abundant pasture, we compare micrometeorological measurements of net methane emission rates with measurements from individual sheep based on a sulphur-hexafluoride tracer technique. Individual sheep emission rates were highly variable and averaged 19.5 ± 4.8 (SD) g CH4 sheep–1 d–1, or 39 ± 9.6 mg CH4 m–2 d–1 on an areal basis. Emission rates were poorly correlated with animal live weight or dry matter intake but represented an average dietary energy loss of 3.6%. Methane fluxes from the surface were determined as half hourly averages by a flux-gradient technique using temperature and methane gradients. Soil methane consumption was measured using chambers and found to be negligible (

Predictions of global climate change have recently focused attention on soils as major sources and sinks for atmospheric CO2, and various methodologies exist for measuring soil surface CO2 flux. A static (passive CO2 absorption in an alkali trap over 24 h) and a dynamic (portable infra-red CO2 gas analyzer over 1–2 min) chamber method were compared. Both methods were used for 100 different site × treatment × time combinations in temperate arable, forest and pasture ecosystems. Soil surface CO2 flux estimates covered a wide range from 0 to ca. 300 mg CO2C m−2 h−1 by the static method and from 0 to ca. 2500 mg CO2C m−2 h−1 by the dynamic method. The relationship between results from the two methods was highly non-linear, and was best explained by an exponential equation. When compared to the dynamic method, the static method gave on average 12% higher flux rates below 100 mg CO2C m−2 h−1, but much lower flux rates above 100 mg CO2C m−2 h−1. Spatial variability was large for both methods, necessitating a large number of replicates for reliable field data, with typical coefficients of variation being in the range 10–60%, usually higher with the dynamic than the static method. Diurnal variability in soil surface CO2 flux was partly correlated with soil temperature, whereas day-to-day variability was more unpredictable. However, use of a mechanistic simulation model of CO2 transport in soil, SOILCO2, showed that very large day-to-day changes in soil surface CO2 flux can result from rainfall events causing relatively small changes in soil water content above field capacity (ca. −10 kPa), even if CO2 production rates remained relatively unaffected.

Effects of elevated CO2 (525 and 700 μL L−1), and a control (350 μL L−1 CO2), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further ‘spring’ period, half of the turves under 350 and 700 μL L−1 were subjected to ‘summer’ drying and were then re-wetted before a further ‘autumn’ period; the remaining turves were kept continuously moist throughout these additional three consecutive ‘seasons’. The continuously moist turves were then pulse-labelled with 14C-CO2 to follow C pathways in the plant/soil system during 35 days. Growth rates of herbage during the first four ‘seasons’ averaged 4.6 g m−2 day−1 under 700 μL L−1 CO2 and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these ‘seasons’ averaged 465, 800 and 824 g m−2 in the control, 525 and 700 μL L−1 treatments, respectively. in continuously moist soil, elevated CO2 had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO2-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO2 produced h−1 mg−1 microbial C was about 10% higher in the 700 μL L−1 CO2 treatment than in the other two treatments. Elevated CO2 had no clearly defined effects on N availability, or on the net N mineralization of added herbage. In the labelling experiment, relatively more 14C in the plant/soil system occurred below ground under elevated CO2, with enhanced turnover of 14C also being suggested. Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously ‘summer’-dried, CO2 production was again higher, but net N mineralization was lower, under elevated CO2 than in the control after ‘autumn’ pasture growth. Over the trial period of 422 days, elevated CO2 generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.

Effects of elevated CO2 (700 μL L−1) and a control (350 μL L−1 CO2) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 μL L−1 CO2 and a temperature 6°C higher throughout than in the other treatments, was included.

Biofiltration, whereby CH(4) is oxidized by methanotrophic bacteria, is a potentially effective strategy for mitigating CH(4) emissions from anaerobic dairy effluent lagoons/ponds, which typically produce insufficient biogas for energy recovery. This study reports on the effectiveness of a biofilter cover design at oxidizing CH(4) produced by dairy effluent ponds. Three substrates, a volcanic pumice soil, a garden-waste compost, and a mixture of the two, were tested as media for the biofilters. All substrates were suspended as 5 cm covers overlying simulated dairy effluent ponds. Methane fluxes supplied to the filters were commensurate with emission rates from typical dairy effluent ponds. All substrates oxidized more than 95% of the CH(4) influx (13.9 g CH(4) m(-3) h(-1)) after two months and continued to display high oxidation rates for the remaining one month of the trial. The volcanic soil biofilters exhibited the highest oxidation rates (99% removal). When the influx CH(4) dose was doubled for a month, CH(4) removal rates remained90% for all substrates (maximum = 98%, for the volcanic soil), suggesting that biofilters have a high capacity to respond to increases in CH(4) loads. Nitrous oxide emissions from the biofilters were negligible (maximum = 19.9 mg N(2)O m(-3) h(-1)) compared with CH(4) oxidation rates, particularly from the volcanic soil that had a much lower microbial-N (75 mg kg(-1)) content than the compost-based filters (240 mg kg(-1)). The high and sustained CH(4) oxidation rates observed in this laboratory study indicate that a biofilter cover design is a potentially efficient method to mitigate CH(4) emissions from dairy effluent ponds. The design should now be tested under field conditions.

Landfills that generate too little biogas for economic energy recovery can potentially offset methane (CH(4)) emissions through biological oxidation by methanotrophic bacteria in cover soils. This study reports on the CH(4) oxidation efficiency of a 10-year old landfill cap comprising a volcanic pumice soil. Surface CH(4) and CO(2) fluxes were measured using field chambers during three sampling intervals over winter and summer. Methane fluxes were temporally and spatially variable (-0.36 to 3044 mgCH(4)m(-2)h(-1)); but were at least 15 times lower than typical literature CH(4) fluxes reported for older landfills in 45 of the 46 chambers tested. Exposure of soil from this landfill cover to variable CH(4) fluxes in laboratory microcosms revealed a very strong correlation between CH(4) oxidation efficiency and CH(4)/CO(2) ratios, confirming the utility of this relationship for approximating CH(4) oxidation efficiency. CH(4)/CO(2) ratios were applied to gas concentrations from the surface flux chambers and indicated a mean CH(4) oxidation efficiency of 72%. To examine CH(4) oxidation with soil depth, we collected 10 soil depth profiles at random locations across the landfill. Seven profiles exhibited CH(4) removal rates of 70-100% at depths

A simple method was developed for measuring phosphorus (P) mineralisation in soil using an anion exchange membrane. Labile inorganic phosphate was first removed from the soil by means of the membrane. The soil samples were then filtered on GF/C papers and incubated moist under aerobic conditions for seven days at 39°C. The inorganic phosphate produced during incubation was extracted using a second extraction with the anion exchange membrane to give a measure of phosphorus mineralisation. The method was applied to 17 soil samples taken from Inceptisols, Andisols, and Spodosols under pasture and pine forest.

The influence of soil allophane (a short-range-order mineral) content on organic-C turnover was determined with 14 C-labelled glucose. Samples from four soils, providing a range of allophane, organic C, clay contents, and some other characteristics, were incubated with 14 C-labelled glucose for 28 days. During incubation, microbial biomass 12 C and 14 C were determined using the fumigation-extraction technique. The amounts of 12 CO 2 and 14 CO 2 evolved during incubation were also monitored, and residual 14 C concentrations determined. Biomass 14 C was highest in the soil with the highest allophane content (13%) and least in the soil with least allophane content ( 14 CO 2 production from the [ 14 C]glucose was highest (63%) in the soil with least allophane content and lowest (54%) in the soil with the most allophane. It was concluded, from first-order decay rate constants for residual 14 C and exponential decay rate constants for biomass 14 C, that allophane retards the turnover rates of 14 C derived from added glucose by stabilization of microbial biomass, and also by protection of microbial products. During a 28 day incubation, ca 0.8% more C was diverted from respired CO 2 to new biomass with each 1% increase in allophane content. For allophanic soils, inclusion of mineral surface area rather than clay content should provide a better quantification of the organic matter turnover rate.

Microbial biomass C and N, and respiratory activity (CO 2 production), declined with sample depth in the strongly acid litter and soil of a southern beech ( Nothofagus spp) forest, at which annual precipitation is about 2000 mm and mean annual air temperature 9.5°C. Microbial C, and generally N, did not differ significantly between spring and autumn samples, possibly because of spatial variability. As a percentage of total C, microbial C was highest ( c 14.5%) in leaf (L) litter, similar ( c 2.1%) in FH material and the topmost soil depths (0–20 cm), but declined to 0.6% in 50–60 cm depth soil; microbial N, as a percentage of total N, declined similarly with sample depth. Microbial C:N ratios were also highest ( c 13) in L material, but were generally similar (mean 6.7) in all other samples. On an area basis, the mass of microbial C and N to 60cm soil depth was c 4220 and 605 kg ha −1 , respectively, with c 14% occurring in the litter layers. The contribution of litter to total CO 2 production on an area basis with roots excluded was, however, c 42%. Temperature coefficients ( Q 10 values) for CO 2 production, determined with 5 and 13°C data, averaged 3.0. Metabolic quotients ( q CO 2 values) were highest in L and FH materials, and were low and similar in the different depths of soil. Generally, q CO 2 values in this old-growth forest were compatible with other values reported for a late stage of ecosystem succession.

The suitability of fumigation-incubation and fumigation-extraction procedures for measuring microbial C and N in strongly acid litter and different depths of soil of a southern beech (Nothofagus spp) forest was investigated. The substrate-induced respiration (SIR) method was also briefly examined. In the fumigation-incubation method, a large inoculum (20% w/w) of unfumigated sample and controls of either fumigated L and FH materials or unfumigated mineral soil incubated for 10–20 days gave maximum CO2-C flush values; controls of unfumigated material incubated for 0–10 days were unsuitable. The kc-factors selected for conversion of CO2-C flush to microbial C depended on sample pH and ranged from 0.28 to 0.44. Use of no control, and a common kc-factor of 0.45, appeared to over-estimate microbial C in L and FH samples, but gave reasonable estimates in the samples of mineral soil. Inoculum size had no detectable influence on mineral-N flush, determined with an unfumigated control. In the fumigation-extraction procedure, increasing fumigation time from 1 to 5 days significantly increased all extractable-N, but not extractable-C, values. Means of experimentally determined kEC-factors, for converting extractable-C flush to microbial C, varied from 0.28 to 0.31 (SD, 0.05–0.09), depending on which 10–20 day control was used in calibration with the fumigation-incubation method. The kEN-factors when calculated in a similar way appeared unrealistically high. The SIR method appeared to under-estimate microbial biomass, when a conventional formula was used for converting CO2 produced to microbial C. Further calibration of the SIR procedure, however, seems warranted. The fumigation-extraction procedure is generally recommended for measuring microbial C and N in these strongly acid samples, using a kEC-factor of c 0.30 and the provisional kEN-factor of 0.45, respectively.

An interlayer clay-organic complex has been isolated from a near-surface horizon of a recent Spodosol from New Zealand. Treatment with hydrogen peroxide selectively removed the organic material attached to external clay surfaces. The radiocarbon age of the treated complex, determined by accelerator mass spectrometry, was 6716 ± 524 years B.P. Since this value refers to the interlayer organic species which has been completely protected against microbial attack, and contamination by “young” carbon, it may be regarded as the “true” age of the soil, that is, the starting point of humus formation and pedogenesis. The interlayer organic carbon comprised approximately 13 percent of the total carbon in the soil horizon. We propose that a biologically inert organic matter (IOM) fraction may be isolated from most soils as this fraction is commonly associated with clay-size particles. Evidence is also accumulating to indicate that IOM is dominantly composed of polymethylenic structures, probably derived from natural waxes, and aliphatic biopolymers present in protective layers of vascular plants. Untersuchung uber Alter, Ort und Art der inerten organischen Substanz eines Spodosols Aus dem Oberboden eines rezenten Spodosols aus Neuseeland wurde ein Zwischenschicht-Ton-Humus-Komplex isoliert. An den Ausenflachen des Tons haftendes organisches Material wurde durch H2O2-Behandlung selektiv entfernt. Das Radiokohlenstoffalter des H2O2-behandelten Komplexes wurde mittels Beschleunigermassenspektrometrie (AMS) auf 6716 ± 524 Jahre BP bestimmt Dieser Wert darf als “wahres” Alter des Bodens, d.h. als Beginn der Humusbildung und Bodengenese angesehen werden, da die organische Substanz innerhalb der Zwischenschichten des Tons ganzlich sowohl vor mikrobiellem Angriff als auch vor Kontamination durch “jungen” Kohlenstoff geschutzt gewesen ist. Der organische Kohlenstoff in den Zwischenschichten umfast ungefahr 13% des gesamten Kohlenstoffs im Bodenhorizont. Wir schlagen daher vor, das eine Fraktion von biologisch inerten organischen Substanzen (IOM) von Boden isoliert werden kann, da diese Fraktion allgemein mit Teilchen der Tonfraktion assoziiert ist. Auserdem gibt es verstarkt Beweise, das die IOM hauptsachlich aus Polymethylen-Strukturen, wahrscheinlich von naturlichen Wachsen herruhrend, und aliphatischen Biopolymeren, die in Schutzschichten von Gefaspflanzen auftreten, zusammengesetzt ist.

Temporal variations in plant production, plant P and some soil P (and N) pools were followed over 21 months in two New Zealand pasture soils of widely different P fertility status. Plant growth rates, and herbage composition at the high-fertility site, were closely linked to soil water use, with growth rates falling when soil water deficits exceeded 60 mm. Herbage P concentrations reflected P fertility, and varied with season, being generally higher in winter and lower in summer.

Humic acids from a total of 14 soils, 10 from New Zealand and 4 from Japan, were selected to provide a range from Rp to A-types. Semi-quantitative assessment of their carbon chemistry by cross polarization magic angle spinning (CPMAS)13C-nuclear magnetic resonance (NMR) revealed variations in composition that were generally related to humic acid type. Aromatic-C was the predominant form of C in most A-type humic acids whereas in Rp, P, and B-type humic acids, the aliphatic-C and aromatic-C contents were comparable. Differences in humic acid types were not always reflected in their carbon chemistry, possibly because of their mode of formation. The effects of fire on vegetation or soil organic matter may at least partly explain the occurrence of A-type humic acids in two different New Zealand soils.

[1] Small mountainous rivers discharge disproportionate amounts of sediment and carbon to the Earth's oceans. Our New Zealand data demonstrates that localized erosion plays a greater role in C budgets than has been recognized in national and global studies. We estimate that New Zealand's rivers export 4 ± 1 Mg C km−2 yr−1 of dissolved organic carbon (DOC) and 10 ± 3 Mg C km−2 yr−1 of particulate organic carbon (POC) (2 and 6 times the global average), which is equivalent to 40% of New Zealand's fossil fuel emissions. Under intact native vegetation in mountain-belt hot spots, POC export greatly exceeds CO2 consumption from mineral weathering. Moreover, deforestation of fertile steepland greatly accelerates POC loss, evidenced by 1.7% of New Zealand's land area which generates 20% of exported POC. Thus, localized erosion deserves increased attention in C budgets and accounting.

[1] We compute the particulate organic carbon (POC) yield of the Waipaoa River, New Zealand, using sediment rating curves in conjunction with measurements of the carbon content of the suspended sediment. To ascertain the source of the carbon and the extent to which the POC flux is tied to different erosion processes, we determined the stable isotopic carbon composition (δ13C) and carbon to nitrogen (C/N) ratio of weathered bedrock, soil, and regolith. Most POC is derived from suspended sediment generated by gully erosion (incision into weathered bedrock), supplemented by landsliding during extreme events. The specific yield of POC from the headwaters (drainage area 1580 km2) is 55 g m−2 yr−1, which is very high by global standards and by comparison with other turbid steep-land rivers. The annual loss to floodplain storage is ∼4% (3.6 Kt) of the mean annual POC yield (86.7 Kt). Thus the Waipaoa River is a very effective conduit for transporting POC to the ocean.

To ensure the sustainability of land systems in terms of nutrient cycling and maintenance of soil physical conditions, there is a need to understand soil organic matter (SOM) and its dynamics. It has been suggested that soil-carbon (C) models developed internationally do not perform well under New Zealand's unique climatic and soil mineralogical conditions. To test this hypothesis, we conducted 14C-labelled ryegrass decomposition studies and assessed the influence of abiotic factors on decomposition rates. These factors were characterized by estimating system mean residence times (MRTs) from estimates of first-order rate coefficients in a simple, three-compartment model. A range of MRTs obtained for decomposition was related to climatic conditions and soil properties. We summarise this work and extend this study to apply the Rothamsted soil-C turnover model, a five-compartment model, to our data with the view of testing both the model projections and the decomposability factors assumed in the model. Keywords: 14C-labelled ryegrass, Climate, Mean residence times, Rothamsted soil-C turnover model, Soil types

Tropospheric methane (CH4) is oxidised by soil microbes called methanotrophs. We examined them in soil samples from a pristine Nothofagus forest located in New Zealand. Laboratory incubations indicated the presence of high-affinity methanotrophs that displayed Michaelis–Menton kinetics (Km = 8.4 µL/L where Km is the substrate concentration at half the maximal rate). When the soil was dried from its field capacity water content of 0.34 to 0.16 m3/m3, CH4 oxidation rate increased nearly 7-fold. The methanotrophs were thus metabolically poised for very high activity, but substrate availability was commonly limiting. When water content was held constant, CH4 oxidation rate nearly doubled as temperature increased from 5 to 12°C, a range found in the forest. By contrast, CH4 oxidation rate did not change much from 12 to 30°C, and it was zero at 35°C. When water content and temperature were held constant, the optimal soil pH for CH4 oxidation was 4.4, as found in the forest. Soil disturbance by nitrogen (N) and non-N salt amendment decreased CH4 oxidation rate, but this depended on the amendment species and concentration. The methanotrophs were adapted to native conditions and exhibited a great sensitivity to disturbance.

The restoration of soil biochemical activities after topsoil removal to depths 0 (S0), 10 (S10) or 20 (S20)cm, and re-establishment of a grass-clover pasture, was studied with Judgeford silt loam, a Typic Dystrochrept, in the Wellington area. Organic matter contents of the S10 and S20 samples were initially 58 and 40%, and biochemical activities, on average, 32 and 20%, respectively of S0 values. Organic matter content increased only slowly in the stripped plots. Yields of pasture herbage, soil CO2 and mineral-N production, three indices of microbial biomass, and invertase, amylase, cellulase, xylanase, urease, phosphatase, and sulphatase activities increased more rapidly, but had not reached S0 levels after 3 yr. The ratios of biomass indices varied with depth of topsoil removed; over the trial, biomass-C to ATP ratios averaged 236, 205, and 168 in the S0, S10, and S20 samples respectively. Biochemical activities were generally correlated significantly with herbage yields in the S10 or S20, but not in the S0 plots; organic C or total N contents were not generally correlated significantly with yields over the first 2 yr. Overall, invertase, and then sulphatase, activity appeared to be the best indicators of soil fertility status in this stripped soil.

Some properties of the humus in, and humic acids from, a number of volcanic ash soils from North Island, New Zealand are presented and compared with those for a range of Japanese soils. In Japanese volcanic ash soils showed, with few exceptions, much higher total organic carbon and humic acid carbon contents than the New Zealand soils. The properties of humic acids in the New Zealand volcanic ash soils were in general well differentiated from those of humic acids in volcanic ash soils from Japan, according to the Japanese system of classification. The humic acids extracted from Japanese volcanic ash soils ware blacker and apparently more humified than those from the New Zealand soils. The humic acids from a number of New Zealand soils were mostly of the B or P type, whereas those from Japanese soils were mostly of the A type. The Ch : Cf ratios were generally high in Japanese soils with humic acid having the highest degree of humification.

Biochemical indices of microbial biomass and other biochemical properties of a Typic Haplaquoll, sampled under pasture over four seasons, were compared in intact cores and soil sieved through a 6 mm and a 2 mm mesh. Sieving had an inconsistent influence on biomass C estimates, which tended, however, to be higher in