Alkali Absorption Method Research Articles

Spatial variability of soil respiration in a larch plantation: estimation of the number of sampling points required

The objective of this study was to determine the spatial variability of soil respiration and the number of the sampling points required to get a representative value of soil respiration within an ecosystem. In late August 2000, two measurements of soil respiration were conducted at a larch ( Larix kaempferi) plantation in Hokkaido, Japan, with the static alkali absorption method (AA method) improved by Kirita [Jpn. J. Ecol. 21 (1971) 119]. The spatial variability of soil respiration rates among 50 sampling points within a 30 m×30 m plot, was described by the coefficient of variation (CV) of each series of measurements. The average CV was 28%. The average number of sampling points required to estimate soil respiration within 10 and 20% of its actual mean, at the 95% probability level, was estimated to be 30 and 8, respectively. Soil temperature and moisture content did not contribute to the spatial variability of soil respiration in the present site, suggesting that these two factors have a greater influence on the temporal variability of soil respiration than on the spatial variability of soil respiration.

Measuring soil respiration in the field: an automated closed chamber system compared with portable IRGA and alkali absorption methods

With the objective of testing whether a series of automated chambers linked to IRGA equipment gave improved estimates of soil respiration, measurements using the automated system were compared with those obtained from (a) an alkali absorption method and (b) a hand-held commercially available instrument (EGM-1). Comparisons were made on occasions between autumn 1996 and spring 1999 across treatment plots which had a variety of harvest residue materials incorporated into them distributed across 5 sites. Spot readings made using the EGM-1 showed a wide range and greater variability compared to those made with the automated IRGA system. This was attributed to the reproducible location and larger area of the latter chamber. The range in values of estimated total daily CO2 flux made using KOH absorption and the automated IRGA method similar (0.1–4.0 g C m− 2 day− 1), but, although highly correlated, the slope of the regression line was significantly different from unity. Below 0.9 g C m− 2 day− 1 the KOH method over-estimated the CO2 flux, but above this value under-estimated it, relative to the automated IRGA system, with the coefficient of variance being consistently smaller for the KOH method. This was ascribed to inefficient absorption of CO2 at high efflux rates and the presence of an artificially high concentration gradient at low efflux rates for the KOH method. The results indicated that the automated IRGA system offered a robust estimate of both instantaneous and time-integrated CO2 efflux rates, and therefore has potential application in measurements of organic matter decomposition in agricultural soils.

Comparison of field methods for measuring soil respiration: a static alkali absorption method and two dynamic closed chamber methods

The objectives of the present study were to compare the static alkali absorption (AA) and dynamic closed chamber (DC) methods for measuring soil respiration, and to evaluate the effects of methodological differences on estimating annual mean soil respiration rate in a natural forest. For the AA method, we used Kirita’s method [Jpn. J. Ecol. 21 (1971) 119] using an alkali-soaked sponge disc that covers nearly the same area as that covered by a chamber. For the DC method, we used both the LI-6200 system (DC-62 method) and the newer LI-6400 system (DC-64 method) (LI-COR, Lincoln, NE, USA). Comparative measurements were conducted on five occasions during the study period (November 1998–October 1999) at a Quercus serrata forest in Japan. Daily mean soil respiration rates obtained by the AA, DC-62 and DC-64 methods for a 24 h period were in the ranges 205–578, 147–629 and 165–734 mg CO 2 m −2 h −1, respectively. The daily mean soil respiration rates obtained by the AA method were 79–128% of those obtained by the DC-64 method. When the daily mean soil respiration rate obtained by the DC-64 method was below 300 mg CO 2 m −2 h −1, the daily mean soil respiration rate obtained by the AA method was an average of 26% higher than that obtained by the DC-64 method. When the daily mean soil respiration rate obtained by the DC-64 method was above 300 mg CO 2 m −2 h −1, the daily mean soil respiration rate obtained by the AA method was an average of 19% lower than that obtained by the DC-64 method. However, at the present site, there was a little difference between the two methods as for estimating annual mean soil respiration rate, and therefore the AA method improved by Kirita [Jpn. J. Ecol. 21 (1971) 119] is suggested to be a useful method for estimating annual mean soil respiration in the forest. The daily mean soil respiration rates obtained by the DC-62 method were systematically 10–24% lower (an average of 15% lower) than those obtained with the DC-64 method, and the annual mean rate was lower than that estimated by the AA method.

Carbon budget study using CO 2 flux measurements from a no till system in central Ohio

Enhancing carbon sequestration in soil is an important means to reduce net emissions of carbon dioxide (CO 2) to the atmosphere. The soil organic carbon (SOC) pool is the net result of carbon (C) input in the form of crop residue and biomass, and output including CO 2 flux and other losses. The objectives of this study were to: (1) determine the influence of known additions of crop residue in a no till system on CO 2 flux measured with the static chamber alkali-absorption method, and (2) calculate the C budget from the CO 2 flux and C added in crop residue. The experiment was started on a Crosby silt loam (Stagnic Luvisol) in 1989. Annually 0, 2, 4, 8 and 16 Mg ha −1 wheat straw ( Triticum aestivum L.) was applied. Noon soil temperature and daily CO 2 flux were determined in 1997. Residue application rate had a significant impact on soil temperature as measured at noon, especially early in the growing season. Noon soil temperature was up to 14°C higher under unmulched compared with that of mulched treatments. Measured CO 2 flux ranged from 0.4 to 4.2 g C m −2 per day. Differences in CO 2 flux between crop residue treatments were not significant on most sampling dates, probably due to the presence of undecomposed residue in the soil which did not contribute to the CO 2 flux, and to variability in sampling. Average daily soil temperature at 5 cm depth determined on a nearby weather station explained 60% of the variation in CO 2 flux from bare plots. The C budget calculated from CO 2 flux measurements indicated a net depletion of SOC in all treatments. However, measured SOC contents indicated an increase of SOC over time in some treatments. It is likely that the annual CO 2 flux measured with the static chamber alkali-absorption method is overestimated due to omission of CO 2 measurements when soil water content is high, and perhaps other, as yet unknown factors. A comparison of the static chamber technique and improved dynamic chamber techniques and micrometeorological methods is recommended.

Examination of four methods for measuring soil respiration

We compared the accuracy of four methods for measuring soil respiration: the open-flow infra-red gas analyzer method (OF-method); the closed chamber method (CC-method); the dynamic closed chamber method (DC-method); and the alkali absorption method (AA-method), using artificial soil medium (vermiculite with glucose and mineral nutrients) inoculated with Trichoderma sp. as respiring microorganisms. The CO 2 emission rates from the medium were measured by the four methods once a day for 10 days. We compared the estimated amounts of glucose respired by Trichoderma sp. (EGR, an integration of measured CO 2 emission rates for 10 days) with the actual amounts of glucose respired (AGR, calculated from weight loss of the medium during the same period). In the AA-method, the EGR value was 1.3 times larger than the AGR value, while in the OF, DC- and CC-methods EGR values were almost the same as the AGR (0.95, 0.95 and 0.94 times respectively). Higher CO 2 emission rates obtained by the AA-method were attributed to low CO 2 concentration (20–250 μl 1 −1) in the chamber, because at such low CO 2 levels the respiration rate of Trichoderma sp. was enhanced by 20–70%. These results indicate that the OF-, DC- and CC-methods are more suitable for soil respiration measurement than the conventional AA-method.

Respiration from soil and litter in a sown perennial grass pasture

The severe nitrogen (N) deficiency which occurs in many sown grass pastures in Queensland is believed to be exacerbated by large and continuous inputs of carbon (C) from decomposing plant residues. In this study we attempted to quantify the importance of surface litter, roots and soil organic matter as sources of respiration in an established green panic (Panicum maximum var. trichoglume) pasture in south-east and Queensland. Intact pasture cores were taken from the field and the surface litter was removed before applying the following treatments: (i) surface litter added, (ii) roots pruned to kill approximately 60% of roots but not kill the plant, and (iii) plant shoots removed. Cores from bare soil between green panic plants were also included. The cores were kept in a glasshouse and CO2 evolution measured continuously for 117 days using an alkali absorption method. Respiration from the various components of the system was estimated. Evolution of CO2 from the cores was increased by litter addition and decreased by shoot removal. Root pruning stimulated CO2 evolution in litter-removed treatments but had no effect in litter-added treatments. Root respiration and microbial respiration of root-derived C accounted for an average of 53% of the total evolved CO2. Surface litter, soil organic matter and dead roots accounted for an average of 40%, 4% and 3% respectively. The importance of a particular C source to microorganisms varied depending on the availability of other C sources. Cores were destructively sampled on five occasions and the soils incubated at 25�C for 10 days to measure CO2 evolution with surface litter and roots removed. Evolution of CO2 in incubated soils was increased by litter and, to a lesser extent, by live roots, demonstrating that some of the labile C from these plant components was soluble or well incorporated into the soil.

Examination of the method for measuring soil respiration in cultivated land: Effect of carbon dioxide concentration on soil respiration

AbstractAn acceleration of soil respiration with decreasing CO2 concentration was suggested in the field measurements. The result supporrs that obtained in laboratory experiments in our previous study. The CO2 concentrations in a chamber of the alkali absorption method (the AA‐method) were about 150–250 parts/106 lower than that in the atmosphere (about 350 parts/106), while those observed in the open‐flow IRGA method (the OF‐method) were nearly equal to the soil surface CO2 levels. The AA‐method at such low CO2 levels in the chamber appears to overestimate the soil respiration. Our results showed that the rates obtained by the AA‐method were about twice as large as those by the OF‐method in field and laboratory measurements. This finding has important consequences with respect to the validity of the existing data obtained by the AA‐method and the estimation of changes in the terrestrial carbon flow with elevated CO2

Effect of carbon dioxide concentration on microbial respiration in soil

AbstractIn order to assess the validity of conventional methods for measuring CO2 flux from soil, the relationship between soil microbial respiration and ambient CO2 concentration was studied using an open‐flow infra‐red gas analyser (IRGA) method. Andosol from an upland field in central Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO2 concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv. Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO2 concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO2 concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium showed a more sensitive response to the CO2 concentration than the filamentous fungi group.

Seasonal pattern of total soil respiration in undisturbed and disturbed ecosystems of Central Himalaya

The rates of CO2 efflux were measured by an alkali absorption method (using 20 ml 0.5 N NaOH) from soils in four undisturbed sites [two evergreen oak forests, Quercus floribunda Lindl. (tilonj oak), Quercus leucotrichophora A Camus (banj oak), and two evergreen conifer forests, Cedrus deodara Loud. (deodar forest) and Pinus roxburghii Sarg. (chir pine forest)] and three disturbed sites. The sites were located between elevations of 1850 and 2360 m in the Central Himalaya. The seasonal pattern of soil respiration was similar in all the sites with a maximum during the rainy season, intermediate rates during the summer season and the lowest level of activity in winter. The rate of CO2 efflux was higher in broadleaf than in conifer forests, and it was lowest in the disturbed sites. Among the edaphic conditions, soil moisture, N, organic C, pH, soil porosity, and root biomass positively affected total soil respiration. The proportion of root respiration to total soil respiration was higher in the disturbed sites than the undisturbed sites in winter. Conditions in the winter season were less favourable for microbial respiration than for root respiration.

Positional, Spatially Correlated and Random Components of Variability in Carbon Dioxide Efllux

AbstractThe ability to distinguish spatial variability either from deterministic trends or from experimental treatment effects contributes to the accuracy and interpretation of field experiments. The objective of this study was to characterize three components of soil and soil plus vegetation CO2 efllux: the positional trend, spatial correlation, and random variation. Soil CO2 efflux was measured in a wheat (Triticum aestivum L.) field at two different dates with differing soil water contents, and soil plus vegetative CO2 efflux was measured at three grassland sites. Carbon dioxide efflux was determined by the alkali absorption method using static chambers located at 3‐m intervals within a 18 m by 18 m square grid. Positional trends were identified using a multiple regression technique, and with a t‐test extended into two dimensions. Data were detrended using a generalized least squares (GLS) regression procedure. Semivariograms were used for analysis of spatial correlation and random variability. The assumption of spatial homogeneity (first‐order stationarity) was not founded for CO2 efflux for four of the five data sets. Positional trends accounted for 16 to 48% of the total variability in these cases. Spatial correlation was not detected, although ignoring positional trends may well have resulted in the opposite conclusion. Spatial structure was affected by the soil water content under wheat. Defining the spatial structure of soil respiration requires determinations under a range of environmental conditions. Advantages of the trend identification and quantification procedures utilized are direct application of common regression techniques, direct evaluation of first‐order stationarity following trend removal and correction for correlated error structure.

Soil Respiration in a Winter Wheat Ecosystem

AbstractRespiration of a silt loam soil (Udollic Ochraqualfs) was studied under cultivation of winter wheat (Triticum aestivum L.) over a 3‐yr period. Evolved CO2 was measured by the alkali absorption method during 24‐h periods at intervals of usually two weeks. Extended estimates of CO2 evolution were made after extrapolating the measured results, in accord with abiotic influences, to include the longer time intervals. Among the abiotic factors examined in relation to evolution of CO2 during the annual agricultural cycle, the most significant was temperature and second, soil water content (R2 = 0.67 for two factors combined). Better models were obtained when the annual cycle was split into two periods, that with predominating plant activity from October through June, and that when CO2 arose solely from the activity of heterotrophs from harvest to planting. Although factors affecting CO2 evolution were the same, predictability increased, and up to 88% of changes in soil respiration during the first period were related to soil temperature and moisture content of the 0‐to 10‐cm layer. For the second period, air or soil temperature plus moisture of the soil at 20 to 30 cm accounted for 76% of the variability. Using models developed for both periods, average annual respiratory loss of C under wheat in Missouri was approximated at 640 g m−2. Maximum soil respiration, presumably from decomposition activity on freshly incorporated residues, occurred during a 56‐d period after harvest, and accounted for 40% of the total annual amount of CO2 evolved from soil. Differences in seasonal patterns of soil respiration and photosynthetic uptake of CO2, indicate that no more than one‐fifth of the photosynthesis requirement for CO2 by winter wheat is produced by soil respiration during the growing season.

Soil Respiration and Carbon Balance in a Tropical Dalbergia sissoo Forest Ecosystem

Summary Soil respiration was measured using the alkali absorption method in a tropical Dalbergia sissoo forest at Kurukshetra. Soil respiration rates showed marked seasonal variations which were attributable to changes in temperature and moisture. The soil respiration rates varied from 90 to 1, 120 mg CO 2 m −2 h −1 , the rates being maximum in rainy season. Positive correlations were observed between CO 2 rates and various abiotic variables (temperature, litter moisture, soil water and rainfall; R 2 = 0.18 to 0.69, P −1 yr −1 ) and carbon output in soil respiration (6, 830 kg C ha −1 yr −1 ) revealed that annual CO 2 -C output was 3.47 times higher than the total input. Loss of carbon in litter decomposition accounted for 86 % of litter production reflecting a meaningful comparison of output and input parameters.