Total and Organic Carbon

A simple ashing procedure for routine determination of soil organic matter is described. Two hundred fifteen soils from 19 states and Canada were ashed at 500° C and the percent weight loss plotted against the percent organic matter determined by Walkley‐Black titration. The resulting regression equation gave a correlation coefficient of 0.98. The organic matter content of experimental samples ranged from 0.64% to 52.4% as determined by the Walkley‐Black method. The proposed procedure incorporates a computerized weighing system and permits 1600 organic matter determinations per day.

A simple high sample volume ashing procedure for determination of soil organic matter

: The purpose of this handbook is to provide state-of-the-art guidance on the subjects of sampling, preservation, and analysis of dredged and fill material. This need developed as a result of the promulgation and implementation of Section 404(b) of Public Law (PL) 92-500 (Federal Water Pollution Control Act Amendments of 1972) which required the ecological evaluation of proposed dredging and filling operations as they may impact navigable waters of the United States. It is expected, therefore, that this manual will receive wider usage as an aid in the regulatory process rather than a research tool. The initial guidance for implementing Section 404(b) was released in 1976. The guidance presented in this handbook should be viewed as second-generation Interim Guidance in the continuing process of procedure development, refinement, and evaluation. Thus, it will be intermediate between the initial Interim Guidance and analytical compediums such as Standard Methods. American Society of Testing and Materials (ASTM) manuals, or Environmental Protection Agency (EPA) manuals. The major emphasis of this effort has been to provide guidance on the subjects of sampling, sample handling, and sample pretreatment.

Procedures for Handling and Chemical Analysis of Sediment and Water Samples

Litter decomposition is an important component of the global carbon and nitrogen cycles. Because climate exerts strong controls over rates of litter decomposition, climate change may alter both cycles. Climate change can influence litter decomposition rates directly, or indirectly through changes in litter quality. The relative importance of climate and litter quality in controlling rates of decomposition varies across ecosystem types. Thus, ecosystem responses to climate change are not readily predictable. This study examines in situ litter decomposition rates of native plant litter of different growth forms (grass, forb, and shrub) in two microclimates (xeric and mesic). In a Colorado subalpine meadow-sagebrush steppe ecotone, a climate-warming treatment was used to determine the influence of litter quality, microclimate, and warming on the rates of decomposition. Three one-year litter bag experiments were performed using senescent leaf litter of the three growth forms from a xeric microclimate (shrub, Artemisia tridentata; grass, Festuca thurberi; forbs, Delphinium nuttallianum, Erigeron speciosus) and a mesic microclimate (shrub, Pentaphylloides floribunda; grass, Festuca thurberi; forbs, Erythronium grandiflo- rum, Ligusticum porteri). A reciprocal transplant litter experiment was performed in the third year to determine the direct effect of warming on litter quality and subsequent litter mass loss rates. Evidence suggests that decomposition was limited by moisture in the xeric zone and by temperature in the mesic zone. Decomposition rates were strongly correlated with the initial lignin:N ratio of the litter. The forbs had a much lower initial lignin:N ratio and, therefore, decomposed at a much higher rate than did the grasses or shrubs. In a changing climate, initial microclimate and changes in litter quality of the bulk litter produced as a result of shifts in species composition may be more important in determining rates of litter decomposition than the direct effect of warming.

Control of litter decomposition in a subalpine meadow-sagebrush steppe ecotone under climate change

The determination of carbon in soils using the Leco CR‐12 resistance furnace has been investigated. The microprocessor‐ controlled furnace, and aspects of its use and performance, are described with particular attention to the routine analysis of soil materials. Some of the effects of furnace temperature, sample weight, fine grinding, ‘comparator’ setting and nature of the carbon on carbon determination and analysis time have been investigated on a range of soils. The furnace method has been compared with a wet oxidation technique and the possibility of characterization of soil carbon ‐ organic and inorganic ‐ was briefly investigated. The system was found to be well suited to soil analysis, being fast, reliable, precise and accurate as well as being easy to use.

The measurement of carbon in soils using a microprocessor‐controlled resistance furnace

Differential thermal analysis shows that in soils organic matter and carbonates react in very different temperature ranges. An automatic CHN Analyzer was therefore used to determine the organic and inorganic carbon content of soils. At 500°C complete oxidation of soil organic matter occurs without appreciable decomposition of carbonates. Because only elemental carbon is determined, interferences due to weight losses from structural water in clays are eliminated. Decomposition of carbonates begins above 500° and always is concluded before 1100°C. Total organic and inorganic carbon in soils thus may be determined by running replicates at 500° and 1100°C with the Analyzer.

G. Giovannini

Papers

Use of an automatic CHN analyzer to determine organic and inorganic carbon in soils