Physical factors influencing decomposition of organic materials in soil aggregates

Glucose or starch labelled with ¹⁴C was mixed thoroughly into slurried soils. Aggregates of different sizes were obtained from the soils as they dried. The labelled substrates were considered to be distributed in both micro- and macropores in the aggregates. Control samples (labelled substrates in macropores only) were prepared by adding the labelled carbohydrates after the formation of the aggregates. The various samples were sterilized by γ-irradiation and stored at ?15°C.Samples were wetted to about ?20kPa, inoculated with soil organisms, and incubated for 4 weeks at 28°C in closed systems, which enabled regular measurement of ¹⁴CO₂ released.Based on the ¹⁴CO₂ released, it was concluded that starch was protected from microbial attack when present in micropores in aggregates made from fine sandy loam.After incubation samples were dried and rewetted. The flush of ¹⁴CO₂ released was twice as big for samples containing labelled starch compared with glucose, showing that disruption of aggregates, containing residual starch, and rearrangements of soil components are as important as chemical and biological factors in causing the flush of CO₂ resulting from wetting a soil. Mechanical disruption of the aggregates resulted in a similar flush of ¹⁴CO₂.     

Autolysis of chlamydospores of Fusarium solani f. sp. cucurbitae in chitin and laminarin amended soils

Lysis of chlamydospores of Fusarium solani f. sp. cucurbitae is enhanced both in chitin and in laminarin amended soils. In soil amended with both chitin and laminarin, lysis of chlamydospores resembles that in control soil. Addition of chitin and laminarin to soil stimulates the growth of both bacteria and actinomycetes. In soils amended with chitin and with both chitin and laminarin, a chitinolytic microflora is stimulated. Penetration of chlamydospore cells by soil microorganisms has not been observed using the electron microscope. The mechanism of lysis of chlamydospores in soil is discussed.     

The wildlife preferences shown by countryside visitors

This study presents the data from part of a questionnaire survey in the Dalby Forest Area, Yorkshire, England. Of nearly 200 species mentioned, visitors hoped prior to their visit that they would see roe deer, badgers, foxes, squirrels, rabbits, pheasants, woodpeckers, kingfishers and adders, but the survey indicated that what they had in fact seen was very different. The number of times that visitors mentioned five groups of wildlife (mammals, birds, plants, trees and insects) altered with four different questions used, indicating that the degree of interaction that a visitor had with these groups varied at different physical, aesthetic and emotional levels.     

Atomic absorption spectroscopic determination of lead extracted from acid-solubilized tissues.

A method is presented for determining lead in a variety of tissues. Lyophilized samples are solubilized with nitric acid at room temperature in glass screw-cap culture tubes. Following neutralization with sodium hydroxide and sodium bicarbonate, the lead is extracted into methyl isobutyl ketone as the pyrrolidine dithiocarbamate complex and analyzed by flame atomic absorption spectrophotometry. Brain, heart, liver, lung, and spleen gave recoveries ranging from 92 to 102% with standard deviations of less than 8%. Aorta, kidney, and rib were unsuitable for analysis by this method. A large number of samples can be analyzed without specialized equipment or intricate experimental steps. The detection limit is 35 ng/g tissue (wet weight) and sensitivity is approximately 140 ng/g tissue (wet weight).     

An outbreak of botulism in gulls on the Firth of Forth,Scotland

The first recorded outbreak of type C botulism in gulls (Larus spp.) in Britain is described. Between June and October 1975, at least 2080 gulls died around the Firth of Forth. The hot dry summer favoured the proliferation of the causative organism, Clostridium botulinum. A definite source of the botulism was not found but prompt removal of the carcases and covering the pools where Cl. botulinum was growing appeared to reduce the mortality. Immunity acquired during widespread exposure to the disease in 1975 may have prevented the reappearance of botulism during the similar climatic conditions in 1976.     

Gas-liquid chromatographic determination of kepone residues in finfish, shellfish, and crustaceans.

Finfish, shellfish, and crustacean samples are extracted with isopropanol and benzene; the extract is filtered and then concentrated. The extract, dissolved in hexane, is treated with oleum and extracted with aqueous alkali. The aqueous phase is acidified and extracted with petroleum ether-ethyl ether (1 + 1). The Kepone residue is determined by electron capture gas-liquid chromatography (GLC). Recoveries obtained by 8 laboratories from 15 species of finfish fortified at 0.02-0.23 ppm ranged from 37 to 107% with a mean +/- relative standard deviation of 79.4 +/- 14.5%. For oysters fortified at 0.01-0.10 ppm, recoveries range from 63 to 129% with a mean of 78.8 +/- 20.8%. For crustaceans fortified at 0.05-0.26 ppm, recoveries ranged from 52 to 110% with a mean of 78 +/- 16.4%. The approximate limits of quantitation for finfish and for shellfish and crustaceans are 0.02 and 0.05 ppm, respectively, under the GLC conditions used in this study.     

Microbiological method for assaying lincomycin in animal feed: collaborative study.

A microbiological assay for determining lincomycin in swine feed, supplement, and a vitamin-mineral premix was studied collaboratively in 16 laboratories. The design of the study involved a complete feed, feed supplement, and a vitamin-mineral premix covering a range of fortification from 20 to 80 g/ton and 80 to 2600 g/ton. Two methods of sample preparation were used depending on the concentration of lincomycin in the sample. Statistical evaluation of the results from the 2 methods indicated that 10 and 11 collaborators, respectively, had mean recoveries which were not significantly different from one another. Ten laboratories obtained a mean recovery of 112.2% (range 102.3--123.5%) for the lower level, and 11 laboratories obtained a mean recovery of 104.4% (range 100.0--107.7%) for the higher level. The method has been adopted as official first action.     

Major mechanisms in formation of spodic horizons

Current explanations of the formation of spodic horizons do not accomodate all features of the horizons in their natural state. In this paper, a more complete explanation of major mechanisms is proposed, using two principles of colloid chemistry: (1) organic substances may form hydrophylic colloids with surface charges, and (2) the hydrophylic character and negative surface charges determine the dispersibility of the colloids. The hydrophylic character is due to the presence of hydrophylic radicals as parts of the organic compounds in soils. The surface charges are the result of dissociation of -COOH and possibly phenol-OH radicals.The neutralization of the surface charge can in principle occur: (1) through electrostatic or physical adsorption and (2) through chemisorption. The first case is typical for monovalent alkali cations. The adsorbed cations are distributed in a double layer, which favours dispersion. Chemisorption occurs mostly with polyvalent cations. This process corresponds in reality to the formation of organo-metallic compounds. It results in a relatively complete disappearance of the double layer and in the formation of large immobile “polymerized” organo-metallic compounds. Because these compounds contain much hydrophylic water, they form a gel. Transition into the solid state is accompanied by the loss of most of the hydration water. The dehydration may be induced by a decrease in thickness of the double layer. At a certain stage of the dehydration process, Van der Waals bonds and protonic bridges can form and bring about a certain degree of hydrophoby.In soils, mobile organic substances are formed during breakdown of plant remains. If at the top of the mineral soil enough polyvalent cations, especially Al and Fe, are available, the mobile organic substances formed are immobilized immediately and no migration occurs. In case insufficient amounts of Al and/or Fe are available to completely immobilize the mobile compounds, these cations are complexed by the mobile compounds and transported downward. Immobilization may occur at some depth through supplementary fixation of cations, through dessication or on arrival at a level with different ionic concentration.In nature, spodic horizons range from loose, with many roots, to very cemented with few roots. These differences can be related to changes in microstructure. Loose spodic horizons have a predominance of polymorphic pellets and aggregates, whereas organans or monomorphic coatings prevail in cemented horizons. The former horizons have many features suggesting major biological influences during their formation, viz., high numbers of roots, thorough mixing of the organic units with clay and silt, the presence of pedotubules and relatively young mean residence times. The latter horizons have features consistent with organo-metallic compounds immobilized in a gel-state, viz., the coatings are strongly cracked, indicating the transition of a gel into a solid; they contain much Al or Al plus Fe but very little or no Si, and the mean residence time is considerably higher than in loose horizons.The two processes seem to operate simultaneously during the formation of spodic horizons and their relative intensities determine the composition of each spodic horizon at any moment in its evolution. As long as the biological activity predominates, the horizon remains loose; if the accumulation of mobile organo-metallic compounds starts to prevail, the horizon is gradually cemented and fossilized.