A comparison of methods of recovering oesophageal extrusa from grazing sheep

Extrusa samples were collected from two groups of oesophageally fistulated sheep grazing together. One group had foam plastic oesophageal plugs fitted below the fistula to assist in the complete collection of extrusa; the second group grazed without plugs. The extrusa were collected in four periods chosen to cover as wide a range of herbage conditions as possible varying from herbage with a high proportion of green leaves to predominantly dry material with a high proportion of dead leaves and stems. The plant components of the extrusa were determined and there was no evidence that stems or any other plant component preferentially by-pass the fistula in grazing sheep. It was concluded that it is not necessary to insert foam plastic plugs in the oesophagus of grazing sheep to obtain representative samples of ingested herbage.     

Effects of organic amendments on evolution of ethylene and other hydrocarbons from soil

Evolution of C₂H₄ from soils under anaerobic conditions was stimulated by amendment with cereal straw, but hay had little effect. Temporary restoration of aerobic conditions resulted in large increases in C₃ and C₄ hydrocarbons, with both straw and hay amendments. Several known products of the fermentative degradation of carbohydrate increased the evolution of hydrocarbons under anaerobic, and to a greater extent, under aerobic conditions. In particular, ethanol and butyric acid promoted the formation of C₂H₄ and propylene, respectively. The association between degradation products and C₂H₄ suggests that both may be implicated when root growth is adversely affected by the anaerobic decomposition of plant residues.     

The use of a comparative particle size distribution index for the numerical classification of soil parent materials: application to mollisols of the argentinian pampa

A method to estimate the magnitude of discontinuities or similarities in parent materials having equivalent mineralogical composition is proposed. It is based on a particle size distribution index which compares for two samples the weight percentages of all fractions taken between selected size limits.The indexes form a matrix and are used to construct a dendrogram which illustrates the clustering into groups. The calculations are carried out by computer using a Fortran programme.The technique was applied to a set of soil samples of Mollisols in the humid undulating pampa in Argentina and good agreement with field observations was obtained.     

The production of N-nitrosoiminodiacetate from nitrilotriacetate and nitrate by microorganisms growing in mixed culture

Mixed populations of microorganisms growing in a recycling soil percolator produced N-nitrosoiminodiacetate (NIDA) after 30 days growth using sodium nitrilotriacetate (NTA), a detergent additive, and NaNO₃ as C and N source respectively. Control experiments using autoclaved soil or substituting either acetate (C source) or NH⁺₄ (N source) did not show any N-nitroso derivative production. Five distinct strains of microorganisms were isolated which could grow on an NTA/NO^?₃ minimal medium but none produced NIDA in pure culture. Mixed cultures of two strains of Pseudomonas produced NIDA after 4 days percolation, using glass beads as a support. Cell-free extracts of the mixed cultures synthesized NIDA after 30 min incubation at 30°C with an activity of 27 μmoles NIDA produced/mg protein h^?1. Physical separation of the two organisms and the cell-free extracts by a dialysis membrane in a chamber determined that only one of the two organisms was responsible for the synthesis of NIDA, but the production was dependent upon the presence of the other organism. The possible relationship between the two organisms is discussed.     

Gas-liquid chromatographic determination of 3,6-dichloropicolinic acid in soils.

A gas-liquid chromatographic (GLC) method has been developed for the determination of the experimental herbicide 3,6-dichloropicolinic acid (Dowco 290) in soils. The method involves extraction of 1 g soil samples with 1N NaCl at approximately pH 7, methylation with diazomethane utilizing a microgenerator, and detection by electron capture GLC. Interferences are small, so that a cleanup step is not necessary even at the 6 ppb level. The procedure is rapid, requiring only 45 min/sample. Recoveries range from 84 to 94% at the 6-1000 ppb level with a minimum detectable limit of 6 ppb. Standard deviations for the percentage recovery values vary from 10.9 to 2.3 for the tested range of 6.7-670 ppb, respectively.     

Resolution of aflatoxins B1, B2, G1, and G2 by high-pressure liquid chromatography.

Aflatoxins were completely resolved as sharp peaks in the order BU-B2-G1-G2 by high-pressure liquid chromatography on a small particle (10 mum) porous silica gel column in 7-13 min (B1 through G2) by a water-saturated chloroform-cyclohexane-acetonitrile elution solvent (25+7.5+1.0), with detection by ultraviolet absorbance at 360 nm. The relationship between peak height and amount injected was linear over a 5-400 ng range for each aflatoxin. Both retention times and peak heights were highly reproducible, multiple injections of mixed standards giving coefficients of variation of 1.0-1.4% (retention time) and 1.6-2.8% (peak height) for the 4 aflatoxins. Detection was highly sensitive, with mean peak height, mm/ng, of 7.1 (B1), 6.4 (B2), 4.5 (G1), and 4.1(G2), allowing detection of 1-2 ng of each aflatoxin.     

Multiple forms of acetyl-naphthyl-esterase activity in soil organic matter

Acetyl-naphthyl-esterase activity has been identified and characterized in organic matter extracted from an A₁ horizon of an Alpine podzol. The temperature optimum of the esterase is about 75° C and its activity rises with increasing pH, without reaching a maximum value in the tested range. The Michaelis constant has been determined as Km = 2.950 mM. Pronase does not disrupt esterase activity. Electrofocusing in acrylamide gel shows several peaks of enzyme activity, which correspond with humic isoelectric bands. The location of acetyl-esterase activity in organic matter is discussed.     

Studies on soil fumigation—III: Effects on enzyme activities,bacterial numbers and extractable ninhydrin reactive compounds

Fumigation of a field soil with chloropicrin and methyl bromide, either singly or in combination, differentially decreased soil enzyme activities and viable bacterial numbers and increased the amounts of ninhydrin reactive compounds extractable with acidified Tris buffer. Chloropicrin treatment was more effective than methyl bromide.The rates of hydrolysis of both an amide and a peptide derivative were decreased by chloropicrin treatment and remained relatively low despite changes in activities over 325 days. By contrast, caseinase activity initially was decreased by both chloropicrin and methyl bromide fumigation, but activities of the fumigated soils recovered to exceed those of untreated soils. Thereafter, caseinase activities of fumigated and untreated soils exhibited relatively large fluctuations, which were partly associated with seasonal drying of the soils in the field.Chloropicrin but not methyl bromide fumigation markedly depressed the viable bacterial populations, which subsequently increased to be above those of the untreated soils. There was no consistent relationship between the release of ninhydrin reactive compounds following fumigation and changes in bacterial numbers or changes in enzyme activity. Autolytic reactions are probably important in the early stages of amino-nitrogen release in fumigated soils. Net gains in caseinase activity may be partly due to the production de novo of extracellular proteases by microorganisms or to the release of intracellular proteases from killed cells.     

Studies on soil fumigation—I: Effects on ammonium,nitrate and phosphate in soil and on the growth,nutrition and yield of wheat

Fumigation of field soil with chloropicrin alone or followed by methyl bromide, each at 220Kg·ha^?1, released 20–30 parts/10⁶ NH⁺₄-N which persisted for 75 days; such fumigation also doubled the amount of bicarbonate-extractable phosphate 28 days after fumigation. Soil fumigation increased both the vegetative and grain yields as well as increasing the content of N in the grain and the content of K and Cl in the tops at ear emergence. Root growth and the phosphate uptake activity of the roots were increased by soil fumigation.