Amelioration of a hardsetting Alfisol through deep mouldboard ploughing, gypsum application and double cropping. I. Soil physical and chemical properties

Contrasting soil management techniques were applied to a hardsetting red-brown earth (Alfisol) used for flood-irrigated wheat (Triticum aestivum) production at Trangie, N.S.W., Australia. The individual and combined effects of deep mouldboard ploughing to a depth of 0.45 m, gypsum application (5 t ha⁻¹) and double cropping upon aggregate stability, bulk density, porosity, cone index and the non-limiting water range were evaluated. Dispersion and slaking of the surface soil were unaffected by the treatments when measured at the end of the second year of the experiment. Approximately 60% of the soil mass in the 0–0.15 m layer slaked on wetting, whereas less than 1% of the soil dispersed. Organic carbon (OC) levels of the surface soil were not affected by double cropping or gypsum application, but were reduced by mouldboard ploughing from 0.9% to 0.6% OC. The relationship between OC and macroaggregate (more than 250 μm) stability indicated that large increases in OC beyond 0.7% OC were required for relatively small increases in aggregate stability. Mouldboard ploughing increased clay content of the upper 0.15 m of the soil from 22% to 27%. This was associated with an increase in the frequency and depth of cracking which, however, diminished over time. The non-limiting water range (NLWR) was expanded in the uppermost 0.1 m by gypsum application from 0.15–0.30 to 0.09–0.28 m³ m⁻³. Mouldboard ploughing expanded the NLWR at a depth of 0.2 m. Penetrometer resistance, on average, exceeded the critical value for wheat root growth at a water content of 0.15 m³ m⁻³, which is substantially higher than the wilting point (0.09 m³ m⁻³). Excessive resistance to penetration as opposed to inadequate aeration or water availability is the main agronomic impediment in these soils, at least in the initial stages of crop development. Penetration resistance within the 0.05–0.3 m layer was reduced during a drying cycle in the order: mouldboard ploughing>gypsum>double cropping. The reduced penetration resistance associated with mouldboard ploughing was due to higher water content to a depth of 0.2 m and reduced bulk density below this depth.     

Earthworm biomass response to soil management in semi-arid tropical Alfisol agroecosystems

Earthworms recorded during 1989–1993 across 15 soil management treatments, comprising three different tillagexthree organic amendments (bare, farmyard manure, and rice straw) and six perennial ley treatments, belonged to two endogeic species, Octochaetona phillotti (Michaelsen) and Lampito mauritii Kinberg, while in a nearby undisturbed natural revegetation area three species were found, including the above two and Octonochaeta rosea (Stephenson). The earthworm biomass showed significant temporal and spatial variations and was higher during the post monsoon period than in the early rainy season. No worm biomass was recorded during the dry season. In the tillage and organic amendment treatments, the biomass was drastically reduced from September 1989 to September 1991 after the application of carbofuran and some herbicides, and was significantly reduced during these two years compared to that of 1992. The maximum monthly earthworm biomass ranged between 2.5 and 17.9 g m^-2 across the treatments and increased several-fold in the nearby natural revegetation area (75.9 g m^-2). It significantly increased in perennial ley treatments compared to annual treatments with organic amendments. Thus the earthworm biomass varied significantly (P<0.01) across the 15 treatments, indicating discernible effects of soil management.Visiting Scientist (under the Rockefeller Foundation Environmental Research Fellowship in International Agriculture)     

Organohalogen residues in human adipose autopsy samples from six Ontario municipalities

Human adipose tissue samples obtained during autopsies in 6 Canadian Great Lakes municipalities were analyzed for chlorobenzenes, polychlorobiphenyls, and organohalogen pesticide residues. The frequency of occurrence and the range and mean for 28 organohalogen residues are reported for male and female donors in each municipality. Overall mean residue values in females were significantly higher than those in males for hexachlorobenzene, beta-HCH, p,p'-DDE,p,p'-DDD + o,p'-DDT, and p,p'-DDT. The means and ranges of residue values were similar to those reported in previous Canadian surveys.     

Loch fleet — a research watershed liming project

A research watershed liming project is being carried out at Loch Fleet in the Galloway District of southwest Scotland. This acid loch originally supported a brown trout fishery, but the number of fish caught by anglers declined during the 1950's and the fishery eventually disappeared about 20 yr ago. After 2 yr of pretreatment data collection, the first set of land time applications took place in the spring of 1986, and the resulting surface water chemical changes are very encouraging. Increases in pH and Ca concentration and decreases in A1 (especially the toxic labile monomeric fraction) concentrations have been observed in the streams and waters draining the treated subcatchments in the loch itself and in the loch outlet. Also, the normal trend for pH and Ca concentration to fall during periods of high flow in the main feeder stream has been reversed. In the spring of 1987, the loch was restocked with brown trout. Initial indications are that there has been very good survival of these fish, and that they managed to spawn during the 1987/88 winter. The chemical and biological changes brought about by the land treatments are described in detail.     

Fluorescent enzyme immunoassay for rapid screening of Salmonella in foods: collaborative study

A collaborative study was performed in 13 laboratories to validate an enzyme immunoassay (EIA) procedure for rapid detection of Salmonella in foods. The EIA was compared with the standard culture procedure for detection of Salmonella in 6 food types: ground black pepper, soy flour, dried whole eggs, milk chocolate, nonfat dry milk, and raw deboned turkey. Uninoculated and inoculated samples were included in each food group analyzed. There was no significant difference in the proportion of samples positive by the EIA and culture procedures at the 5% level for any of the 6 foods. The enzyme immunoassay screening method has been adopted official first action as a rapid screening method for detection of Salmonella.     

Cation type and ionic strength effects on the solution composition of an acidic subsoil

Sodium, potassium, magnesium and calcium chloride solutions of four concentrations (0.4, 1.0, 4.0, l0.0meq dm⁻³) and distilled water were equilibrated with the highly weathered, acidic subsoil of a Plinthic Paleudult from Natal at a soil:solution ratio of 2.2:1, then separated by centrifugation with an immiscible liquid and analysed for inorganic solutes. With each salt, increasing ionic strength resulted in lower solution-pH (the maximum pH was 4.95 in the distilled water equilibration) and higher aluminium concentration and activity. These effects were much less marked for sodium (maximum ΔpH of 0.47) than for the other cations (maximum ΔpH of 0.83) and both the concentration and activity of aluminium were correspondingly lower (by tenfold at the highest chloride concentration) in the sodium solutions.
Irrespective of the nature or concentration of the electrolyte added, pH and the activities of A1³⁺ and silica in solution were consistently interrelated in a way which suggests that equilibrium with the gibbsite and poorly crystalline kaolinite in this soil had been closely approached. The results provide a basis for anticipating the effect of infiltrating solutions of fertilizer salts on subsoil acidity and suggest that a beneficial effect may accrue from the presence of sodium in the cation suite of acid soils.     

Response of the pigeonpea-Rhizobium symbiosis to salinity stress: variation among Rhizobium strains in symbiotic ability

Summary There were significant differences among pigeonpea [Cajanus cajan (L.) Millsp] Rhizobium sp. strains (IC 3506, IC 3484, IC 3195, and IC 3087) in their ability to nodulate and fix N₂ under saline conditions. Pigeonpea plants inoculated with IC 3087 and IC 3506 were less affected in growth by salinity levels of 6 and 8 dS m^-1 than plants inoculated with the other strains. For IC 3506, IC 3484, and IC 3195, there was a decrease in the number of nodules with increasing salinity, while the average nodule dry weight and the specific nitrogenase activity remained unaffected. However, in IC 3087, the number of nodules increased slightly with increasing salinity. Leaf-P concentrations increased with salinity in the inoculated plants irrespective of the Rhizobium sp. strain, and leaf-N concentrations decreased with increasing salinity in IC 3484 and IC 3195 only. Shoot-Na and-Cl levels were further increased in these salt-sensitive strains only at 8 dS m^-1. Therefore there may be scope for selecting pigeonpea Rhizobium sp. symbioses better adapted to saline conditions. The Rhizobium sp. strains best able to form effective symbioses at high salinity levels are not necessarily derived from saline soils.Submitted as JA No. 919 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Determination of benzene in polypropylene food-packaging materials and food-contact paraffin waxes

An analytical procedure was developed for determination of benzene in polypropylene food packaging and was adapted for determination of benzene in commercial paraffin waxes intended for food-contact use. The polymer was dissolved in hexadecane at 150 degrees C. The wax was melted in an 80 degrees C oven. A simple helium-sparging apparatus was used to remove the volatile chemical from the polymer or wax. The contaminant was collected in methanol, distilled water was added, and the resulting solution was analyzed by headspace gas chromatography. The instrument was equipped with a 30 m fused silica open tubular capillary column and a photoionization detector. Average recoveries of benzene from polymer and paraffin wax at low parts-per-billion concentrations were 63 and 70%, respectively. Limits of detection and quantitation for analysis of polypropylene were 8 and 17 ppb, respectively; the limit of quantitation for analysis of paraffin wax was 2 ppb. In several commercial polypropylene products examined, benzene levels ranged from none detected to 426 ppb. In 3 commercial waxes examined, concentrations of 16-73 ppb benzene were determined. The presence of benzene was confirmed by gas chromatography/mass spectrometry.     

Soil Ca, Al, acidity and penetration resistance with subsoiling, lime and gypsum treatments

Abstract. Crop growth on strongly weathered soils is often limited by soil compaction in addition to aluminium toxicity and/or calcium deficiency. This study examines the effects of subsoiling, lime and gypsum on penetrometer resistance, acidity, aluminium and calcium levels and cotton ( Gossypium hirsutum L.) root growth on soils transitional between Cecil and Appling series (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont region of Georgia, USA. The main plots were subsoiled to depths of 0.35 or 0.80 m or untreated. Dolomitic limestone (0 or 4.03 t per hectare on subplots) and phosphogypsum (0 or 10 t per hectare on sub-subplots) were incorporated into the surface soil (0.15 m). Deep subsoiling (0.80 m depth) decreased penetrometer resistance at 0.3–0.5 m depth and increased yield in two of three years, but there was no response to shallow subsoiling (0.35 m depth). Lime increased yield when surface soil water pH prior to amendment was less than a Cate-Nelson critical value of 4.6. Gypsum moved downward much more rapidly than lime, increasing soil solution calcium ion activity to a depth of 0.8 m within 5 months of application. There were differences in clay content between replicate plots and calcium movement was faster where the clay content was less. Yield responses to gypsum in 1986 were attributed to increased root growth below 0.2 m resulting from the increased calcium ion activity. Yield response to gypsum in limed sub-subplots was significant only in 1986.     

Soil amidase activity in polyacrylamide-treated soils and potential activity toward common amide-containing pesticides

 Polyacrylamide (PAM) is currently used as an irrigation water additive to significantly reduce the amount of soil erosion that occurs during furrow irrigation of crops. Elevated soil amidase activity specific toward the large PAM polymer has been reported in PAM-treated field soils; the substrate specificity of the induced amidase is uncertain. PAM-treated and untreated soils were assayed for their capacity to hydrolyze the amide bond in carbaryl (Sevin), diphenamid (Dymid), and naphthalene acetamide. Based on results obtained with a soil amidase assay, there was no difference between PAM-treated and untreated soils with respect to the rate of amide bond hydrolysis of any of the agrochemicals tested. It appears that under these assay conditions the PAM-induced soil amidase is not active toward the amide bonds within these molecules. However, carbaryl was hydrolyzed by a different soil amidase. To our knowledge, this is the first soil enzyme assay-based demonstration of the hydrolysis of carbaryl by a soil amidase. Received: 23 June 1999