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Results from earlier laboratory and field experiments were interrogated for the possibilities of sequestration, or long-term accumulation, of carbon from excess greenhouse gases in the atmosphere. In the laboratory study, samples of three (top) soils dominated by kaolinite and illite (together), smectite, and allophane were examined for the adsorption and desorption of dissolved organic carbon (DOC). Adsorption and desorption of DOC were carried out on clay fractions extracted physically and after first native organic matter and then iron oxides were removed chemically. Labeled organic material was added to the soils to assess the priming effect of organic carbon (OC). In the field, changes in OC were measured in sandy soils that had been amended by additions of clay for between 3 and 17 years, both through incorporation of exogenous clay and delving of in situ clay. The laboratory experiments demonstrated that a portion of DOC was held strongly in all soils. The amount of DOC adsorbed depended on clay mineral types, including Fe oxides. Much adsorbed DOC was lost by desorption in water and a substantial amount of native OC was lost on priming with new OC. Addition of clay to soils led to increased OC. Therefore, addition of clay to soil may enhance net sequestration of C. Organic carbon close to mineral surfaces or within microaggregates is held most strongly. Carbon sequestration may occur in subsoils with unsaturated mineral surfaces. However, incorporation of carbon into macroaggregates from enhanced plant growth might be most effective in removing excess carbon from the atmosphere, albeit over the short-term. [ABSTRACT FROM AUTHOR]

In agricultural soils, subsoil clay addition to sand has the potential to improve carbon sequestration by increasing soil organic carbon (OC) concentration through adsorption and occlusion. However, the factors influencing increased OC in these engineered soils are poorly understood. The addition of subsoil clay creates clods of different sizes, from a few mm up to 200 mm or more in diameter. This study assessed the i) size, number and vertical distribution of clods and OC at two clay-modified field sites and ii) effect of clod size and properties on OC in incubation experiments. The hypotheses were that smaller clods would increase and stabilise OC more than larger clods and that an even distribution of clods throughout the depth of modification will increase OC stock compared to patchy distribution. Two field sites with differing clay modification method, delved and spaded, were studied. Soil was excavated from a 30 cm quadrat in 10 cm increments down the profile, sieved into clod sizes and mass with clod number and OC concentration determined. Delving elevated clay from 40 to 60 cm depth and created few clods, which were poorly distributed in the depth of modification. Spading mixed clay from 20 to 30 cm below the soil surface and created many, smaller sized clods, which were more evenly distributed within the 0–30 cm modification depth. OC concentration was highest in the smallest clods, particularly at the soil surface. OC stock increased with clod number. Clods collected from the two field sites were further used in incubation experiments to determine the effect of clod size and properties (clay and iron concentration) on the accumulation and protection of OC. Clods (2–6 and 6–20 mm) were added to sand at 80 mg clay g −1 sand and incubated 300 or 420 days at optimal moisture conditions with monthly wheat residue addition in the accumulation experiment. Smaller clods (2–6 mm) accumulated OC at a higher rate and offered greater protection from decomposition by microbes than larger clods (6–20 mm). These results support our hypotheses that smaller clods and even vertical distribution is important to increase OC. Furthermore, clod number was a critical factor in increasing OC content. We conclude that in clay-modified soils the addition of many, smaller sized clods distributed throughout the depth of modification can improve OC content. [ABSTRACT FROM AUTHOR]

This article considers the aesthetic views of Delvig as a critic and identifies the sources that help him develop individual criteria for assessing literary works. The author emphasises his original interpretation of theoretical problems of aesthetics characteristic of Romanticism. It is stressed that the category of harmony defined by Delving as a crucial principle of artistry is very productive in his system of views and underlies his own poetry.