A comparison of four methods for measuring respiration in organic material

Four methods for measurement of respiration (CO₂ evolution) were compared on uniformly prepared, birch forest-floor organic matter; the methods included infrared gas analysis (i.r.g.a.), gas chromatography (g.c.), KOH absorption of CO₂ (b.a.) and the Gilson respirometer. Respiration estimates were made at a single temperature and also at variable temperatures at constant moisture contents. The i.r.g.a. and b.a. methods gave maximum estimates for respiration; the g.c. gave lowest, with the Gilson intermediate. Lower estimates for the g.c. are attributed to the closed system employed, which included no means of increasing gas diffusion (such as a KOH-CO₂ sink or continuous gas flow) out of the sample into the unoccupied space of the respiration chamber.At 25°C, the minimum sensitivity of the g.c. and Gilson were 3.8 and 3.6 μg CO₂, respectively. The minimum sensitivity of the b.a. method (44 μg CO₂) could have been improved with use of a micro-liter burette for titrations. The least minimum sensitivity, 0.31 μg CO₂, was attained with the i.r.g.a.Conditions under which any of the techniques may be used to estimate respiration should be carefully worked out. The relationship between sample size, gas flow rate (open system), chamber atmosphere composition (closed system), and chamber design should be established with sufficient confidence so that stimulation of respiration by excessive gas flow rate, or exhaustion of O₂ or CO₂ inhibition through extended chamber closure does not adversely affect respiration estimates.     

A comparison of soil and water properties in organic and conventional farming systems in England

Organic farming and improvements to agricultural sustainability are often seen as synonymous. However, an extensive European review demonstrated that in practice this is not always true. This study aims to compare the status of soil and water properties between separate fields managed in either an organic or a conventional manner. Soil samples were collected from 16 pairs of farms, throughout England, with both arable and grass fields within each pair on similar soil type. Chemical (nutrients, pesticides, herbicides) and physical (aggregate stability, field capacity, shear strength, soil organic matter, infiltration rates) soil properties were measured in four main soil texture classes in organic and conventional fields. The physical soil properties varied significantly between the different classes of texture and land use. The heavier textured soils have significantly higher soil organic carbon (SOC), aggregate stability and shear strength. The coarse‐textured soils have significantly lower field capacity moisture contents. The grassland has a significantly higher level of SOC, field capacity moisture content, aggregate stability and soil shear strength. However, there were no significant differences between organic and conventional treatments for any of the soil physical properties measured. There were fewer traces of agrochemicals in the soil water from the organic fields compared with the conventionally managed fields. The conventional arable fields had higher levels of total inorganic nitrogen than the other land uses and treatments. There was evidence to show that infiltration rates were significantly higher on organically managed grassland soils (7.6 mm/h) than conventionally managed grassland (2.5 mm/h) with lower stocking rates. The results suggest that improved grassland management, whether organic or conventional, could reduce predicted runoff by 28%.     

Inadequate intakes of dietary zinc among pregnant women from subsistence households in Sidama, Southern Ethiopia

OBJECTIVE: To assess the prevalence of zinc inadequacy based on dietary intakes and plasma zinc concentrations and, simultaneously, the prevalence of inadequate intakes of energy, protein, calcium and iron. DESIGN: A cross-sectional study of a convenience sample of subsistence farming households in Sidama, Southern Ethiopia. SUBJECTS: Dietary intakes were calculated from 1-day weighed food records and 40 repeats from 99 pregnant women in the third trimester using analysed values of major staple foods for zinc, iron, calcium and phytate. The distribution of observed intakes was adjusted for usual intakes and the prevalence of inadequacy estimated using the estimated average requirement (EAR) cutpoint method. Prevalence of inadequacy for zinc, protein and iron intakes were compared with those based on biochemical measures. RESULTS: Prevalence of zinc inadequacy was very high: 99% for US FNB EAR and 100% for IZiNCG EAR compared to 72% based on low plasma zinc concentrations. Corresponding prevalence estimates for iron were much lower: 4% for inadequate intakes based on US FNB EAR vs. 8.7% for iron deficiency anaemia (haemoglobin < 110 g l-1; ferritin < 12 microg l-1) and 32.3% for low storage iron. Prevalence of inadequacy for protein was 100% for adjusted intakes and 91% for serum albumin < 32 g l-1. For calcium, 74% were at risk for inadequate intakes. CONCLUSION: The high prevalence of inadequate intakes of zinc and protein was reasonably consistent with those based on biochemical measures. Such dietary deficits could be overcome by regular consumption of cellular animal protein. In contrast, both dietary and biochemical measures of iron inadequacy were low.     

A comparison of methods for measuring aluminium in KCl extracts of soils

Abstract

Five colorimetric methods; alzarin red, aluminon, catechol violet, ferron and 8‐hydroxyquinoline, and AAS were compared for measuring aluminium in KCl extracts of soils. An analysis of variance of the results against soils, methods and replicates showed that, apart from the predictably large soil effect, the three two‐way interactions and the method effect gave small but statistically significant differences.

The AAS method showed the most variation, and the catechol violet method gave consistently lower results than the other methods, but provided differences in the order of 10% are not considered critical, any of these methods could be used on a routine basis.     

Sampling for ants in different-aged spruce forests: A comparison of methods

It is necessary to use special sampling method for studying of each animal group. However each method has its specificity and describes the studied community a bit differently. Three common methods for sampling of ants were compared: soil excavation, pitfall traps and baits. Ants were sampled in 25 patches in a large spruce forest in the Czech Republic during 2005 and 2006. Each patch represented one of five age classes (0–2, 3–5, 8–12, 26–41 and 85–105 years old), and the patches were located in five sites such that the five patches in each site formed a chronosequence. The percentage of variability in ants as explained by other sampling techniques was as follows: 60.0% of the variability in bait data was explained by pitfall trap data, while only 19.7% of the variability in pitfall trap data was explained by excavation data. Species and numbers of ants on baits were strongly affected by bait type: Myrmica species preferred honey whereas Formicinae preferred tuna bait. Assembly composition in pitfall traps varied significantly between study sites. The position of sampling site in landscape (location in the forest regardless of the immediate habitat type where the trap was located) hence strongly affected ants. Proportions of ants in particular methods were equal in the majority of cases. For excavation samples, ant numbers and species were more influenced by the immediate habitat than the wider habitat, but the opposite was true for samples from pitfall traps.     

A comparison of methods for estimating fractional vegetation cover in arid regions

We compared a set of methods for estimating the fractional vegetation cover (f_c) of sparse desert vegetation over an arid region of southern Xinjiang, China. Six kinds of remote sensing inversion models (an NDVI regression, a spectral mixture analysis (SMA), a pixel dichotomy model, a three-band maximal gradient difference (TGDVI) model and two modified TGDVI models) were used to derive f_c from remote sensing data, and the results were compared with f_c values measured in the field to select an appropriate model to derive the fractional cover of sparse desert vegetation in arid regions. The NDVI regression based on field f_c and the NDVI for the sampled pixels in September 2006 showed the highest precision, while the results of 2007 showed that the NDVI regression method is inappropriate for depicting vegetation characteristics in other growing season because the empirical model highly depend on the specified in situ measurement. The SMA approaches yielded higher precision than the other models, indicating that it is applicable for analysing the coverage of sparse desert vegetation. The pixel dichotomy model can yield a high precision based on finely detailed vegetation maps. However, it requires the measurement of many parameters. The TGDVI model is simple and easy to implement, and the values that it predicted for the coverage of high-density vegetation and barren areas were close to those measured in the field, but the f_c values of sparsely vegetated areas were underestimated. The predictions of the modified TGDVI models were close to the values measured in the field, indicating that these modified models can reliably and effectively extract information on the fractional cover of sparse vegetation in an arid region. We analyzed the models’ sensitivity with respect to rainfall because the short-wavelength infrared bands used in the two TGDVI models proposed in this study are sensitive to moisture. The results showed that the modified TGDVI models’ accuracy was not affected by increasing soil moisture content caused by rain. However, the NDVI regression, SMA and TGDVI were sensitive to the change of soil moisture content. Moreover, the two modified TGDVI models yielded negative values for water sources, such as reservoirs and rivers, implying that they are effective for characterising water bodies. However, the modified TGDVI models cannot predict f_c in snow- and glacier-covered regions, producing abnormally high rather than zero values. Additionally, the predictions before and after snowfall on the top of a mountain show a linear increasing relationship, suggesting that the short-wavelength infrared band may be useful to predict snow depth.     

A comparison of some methods for soil organic carbon determination

Abstract

This study compared three dichromate‐oxidation methods adapted for use with 100‐mL digestion tubes and 40‐tube block digester (for controlled heating), the Walkley‐Black method, a loss‐on‐ignition procedure and an automated dry combustion method for the determination of organic carbon in soils of the northwestern Canadian prairie. The Walkley‐Black method required a correction factor of 1.40. The modified Tinsley method and the Mebius procedure, adapted for use with 100‐mL digestion tubes, recovered 95% and 98%, respectively, of soil carbon against the dry combustion procedure. The presence of elemental carbon in some soils probably caused, at least partially, the slightly incomplete recovery; thermal decomposition of dichromate may not have been accurately corrected for. A dichromate‐oxidation procedure with controlled digestion at 135°C gave 100% recovery, but somewhat more variable results. The loss‐on‐ignition procedure, even when allowance was made for clay content of the soils, was the least satisfactory of the methods tested. All procedures produced correlation coefficients of 0.980 or better against the dry combustion method.     

北方农牧过渡带农户农业生产系统模式评价与优化研究

以内蒙古赤峰市为例,采用切诺斯评价法对北方农牧过渡带典型地区的偏牧区、偏农区和半农半牧区3种类型区常见的6种家庭农业生产系统模式进行了社会经济效益、生态效益和资源利用效率的系统评价与优选,结果表明草地畜牧业和养猪模式、种植业和育肥牛模式、农牧结合模式效益较好,并针对3种模式存在的问题提出优化改良方案,改良后的优化模式分别比原模式户均收入提高26．8％、81．0％和46．9％,投资效益提高4．7％、7．1％和4．2％;产出总能分别提高27．0％、77．0％和70．5％;光能利用率分别提高14．6％、23．8％和47．6％。     

A critical assessment of methods for determining organic phosphorus in savanna soils

 Two newly introduced extraction techniques for determining total organic P (P₀) were compared with the standard high-temperature ignition method in selected savanna soils of Nigeria. The two extraction techniques were: (1) concentrated H₂SO₄ and dilute base sequential extraction (18 N H₂SO₄ and 0.5 N NaOH) and (2) basic EDTA method (0.25 M NaOH plus 0.05 M Na₂EDTA). The concentrated H₂SO₄ and dilute base method extracted significantly higher total P₀ than the high-temperature ignition method and the basic EDTA extraction. The high-temperature ignition and the basic EDTA extraction gave similar total P₀ values (mean=91 mg kg^–1 for ignition and 90 mg kg^–1 for basic EDTA). The precision of the methods, determined by coefficients of variation (CV, %) associated with each P₀ determination method in the soils, was better for the concentrated H₂SO₄ and dilute base extraction method (CV=13%) than the ignition method (CV=18%) and the basic EDTA method (CV=15%). The high C : P₀ ratios determined for the high-temperature ignition and basic EDTA extraction indicated that the two methods underestimated total P₀ in the soils. The concentrated H₂SO₄ and dilute base sequential extraction appears to be suitable for the rapid determination of P₀ in savanna soils because the method can be simplified to a single-step analysis. Received: 14 November 1997     

An assessment of subsoil organic carbon stocks in England and Wales

It is estimated that half the soil carbon globally is in the subsoil, but data are scarce. We updated estimates of subsoil organic carbon (OC) in England and Wales made by Bradley et al. (2005) using soil and land‐use databases and compared the results with other published data. We estimated that the soils of England and Wales contained 1633, 1143 and 506 Tg of OC at 0–30, 30–100 and 100–150 cm depths, respectively. Thus, half of the soil OC was found below 30 cm depth. Peat soils accounted for the largest proportion, containing 44% of all the OC below 30 cm despite their small areal extent, followed by brown soils, surface‐water gley soils, ground‐water gley soils and podzolic soils. Peat soils had more than 25% of their profile OC per unit area in the 100–150 cm depth, whereas most other soils had <8% at this depth. The differences between soil types were consistent with differences in soil formation processes. Differences in depth distributions between land uses were small, but subsoil OC stocks in cultivated soils were generally smaller than in soils under grassland or other land uses. Data on subsoil OC stocks in the literature were scarce, but what there was broadly agreed with the findings of the above database exercise. There was little evidence by which to assess how subsoil OC stocks were changing over time.     

A comparison of wet oxidation methods for determination of total phosphorus in soils

For 15 soils with widely different extractability of phosphorus (P) two newly introduced digestion techniques for determining total P (P_t) were compared with the standard perchloric acid digestion procedure. The two digestion techniques were: (1) concentrated H₂SO₄ plus 30 % H₂O₂ at 360 °C, (2) concentrated HCl plus concentrated HNO₃ in the ratio 3:1 (aqua regia) at 140 °C. Almost equal amounts of P_t were extracted by the two methods (mean = 188.7 mg kg^—1 for H₂SO₄/H₂O₂ and 188.4 mg kg^—1 for aqua regia) which were slightly higher than the standard method (mean = 183.8 mg kg^—1). However, there is no statistical difference among the three digestion methods, suggesting that the tested methods should be useful for estimating P_t in soils with high content of organic C, eliminating the danger of explosion when hot concentrated HClO₄ is used.     

A comparison of methods used for determination of cation exchange capacity

Abstract

Cation exchange capacity of ten non‐calcareous and non‐saline soils from Queensland, Australia, has been determined by the ammonium acetate method using different procedures, by an ammonium chloride method at pH8.5, and by three methods which attempt to approximate field conditions. Procedural differences in the ammonium acetate method produced variation in results, and methods using approximate field conditions gave much lower values for those soils considered to have variable charge properties.     

四类全球土地覆盖数据在中国区域的精度评价

该研究以中国耕地类别为研究对象,选择2000年中国土地利用数据（NLCD-2000）为参考数据,利用比较分析法,从面积数量精度和空间位置精度两方面对目前4类全球土地覆盖数据（UMD、IGBP-DISCover、MODIS和GLC2000）产品进行了精度验证,并分析研究了4类数据精度的异同性。结果表明,4类全球数据对中国耕地数量特征和空间位置特征的估测具有明显的区域差异性。MODIS数据集和GLC2000数据集对中国耕地制图的总体精度要高于UMD数据集和IGBP-DISCover数据集。4类数据制图精度高的区域主要分布在中国的农业主产区,而误差大的区域主要分布在中国山区或耕地比例低的区域。低空间分辨率的信息源、基于像元的分类方法,以及中国复杂地形特征是4类全球土地覆盖数据精度差异的主要原因。     

A comparison of methods for soil microbial population and biomass studies

A comparison was made of 15 different techniques which are used in assessing soil microbial populations and/or biomasses. These include direct observations (fungal standing crop, fluorescein diacetate active mycelia, acridine orange stained bacteria), cultural methods (bacterial plate counts), physiological methods (total microbial, bacterial and fungal biomasses, O₂-uptake), soil enzyme analyses (dehydrogenase, catalase, alkaline and acid phosphatase, protease, amylase), and ATP-analyses. The various techniques were applied to six soils known to have different microbial characteristics. The results are discussed with respect to the convertability of counts and measurements into microbial biomasses, the variability of the techniques, the correlations within comparable groups of methods, and the practical limitations in application of individual methods to different soils.     

Exchangeability of phosphate extracted by four chemical methods

Isotopically exchangeable phosphate (P) is a major source of P for plants. In practice, however, plant‐available P is assessed by chemical extractions solubilizing a mixture of P forms the availability of which is ill defined. We undertook an isotopic approach to assess the exchangeability of P extracted by (1) CO₂‐saturated water (P‐CO₂), (2) ammonium acetate EDTA (P‐AAEDTA), and (3) sodium bicarbonate (P‐NaHCO₃) compared to the exchangeability of P extracted by water. Five topsoils with similar P‐fertilization histories but different soil properties were studied. Phosphorus was extracted from soils labeled with carrier‐free ³³P after 1 week of incubation, and the specific activity (SA = ³³P / ³¹P) of the extracts was compared with the SA of P extracted by water to calculate the amount of P isotopically exchangeable that had been solubilized during the extraction. P‐CO₂ extracted between 20 and 100 times less P than P‐AAEDTA and P‐NaHCO₃. The SA of P‐CO₂ was not different from the SA of water‐extractable P, showing that P‐CO₂ solubilized similar forms of P as water and that these forms can be considered as available. The SA of P extracted by the two other methods ranged between 25% and 63% for P‐AAEDTA and 66% and 92% for P‐NaHCO₃ of the SA of water‐extractable P. The fraction of exchangeable P extracted by AAEDTA decreased linearly with increasing soil pH, suggesting that this method dissolves slowly or non‐exchangeable P from calcium phosphates.