Inoculation of pines with mycorrhizal fungi in natural soils—I.: Effects of density and time of application of inoculum and phosphorus amendment on mycorrhizal infection

On two soils lacking fungi capable of forming mycorrhizas with Pinus, the addition of superphosphate at 40 kgP/ha greatly increased mycorrhiza formation in Pinus radiata D. Don and P. elliottii Little and Dorman. Phosphorus could be partially replaced by increasing inoculum density or avoiding delay in inoculation after sowing. Chlamydospores were less effective than basidiospores as inoculum except at the highest density and in the presence of added P. At low available P concn such as are common in Australian soils, the normal pattern of infection of new short roots is interrupted and re-infection from the soil is of greater importance. Survival of mycorrhizal fungi in the soil in the absence of the host may therefore be a critical factor in inoculation programs.     

Changes in enzymic activity and distribution of acid-soluble,amino acid-nitrogen in soil during nitrogen immobilization and mineralization

During a period of immobilization of nitrate-¹⁵N and mineralization of organic N in a sandy-loam, changes were recorded in: (a) the concentration of an added carbon source, glucose-¹⁴C: (b) evolution of ¹⁴CO₂: (c) bacterial populations; (d) distribution and concentration of newly-synthesized, acid-soluble, amino acid-¹⁵N; and (e) distribution and activities of several oxidative and hydrolytic enzyme systems.Added glucose-¹⁴C was rapidly metabolized by the soil microflora. After 1.5 day's incubation, when only 3.6 per cent of the added glucose was present, 68 per cent of the ¹⁴C remained in the soil-microbial system. During this period there was a marked increase in viable bacterial numbers and an almost complete immobilization of nitrate-¹⁵N. On continued incubation, microbial metabolites were oxidized at decreasing rates, the more rapid phase corresponding to a period of net decline in the viable bacterial population.Soil was fractionated by a relatively mild procedure into components containing: (a) extractable proteins; (b) extractable amino acids and peptides; (c) particulate material containing microbial cells, cell debris and material bound to larger soil particles; and (d) microbial metabolites mainly bound to soil colloids. Although the total, acid-soluble, amino acid-¹⁵N remained relatively constant for about 50 days, there were marked changes in their concentration in different fractions, especially in the extracts and in the fraction containing fine colloidal material. However, the relatively large decline in labelled, acid-soluble, amino acid-¹⁵N occurred during the active phase of oxidation of microbial metabolites when little net mineralization of labelled compounds occurred.Increases in enzymic activities generally coincided with increased viable bacterial populations although there were some exceptions, notably casein and benzoyl arginine amide-hydrolysing enzymes. The stabilities of the newly-formed enzymes varied markedly. The greatest relative changes in activity occurred with the casein-hydrolysing enzymes. Their activity reached a maximal value after the main flush of bacterial growth, was short-lived and was to a large extent extractable. The formation and disappearance of this extracellular proteolytic activity coincided approximately with that of a secondary peak of extractable, newly-synthesized, protein-¹⁵N. In general however, changes in enzymic activity could not be identified with changes of protein-¹⁵N concentrations of the different fractions.     

A COMPARISON BETWEEN A PADDOCK SYSTEM AND A 'WYE COLLEGE' SYSTEM OF GRAZING FOR MILK PRODUCTION

Two grazing systems, a paddock system and a ‘Wye College’ system, were compared in two 20-week experiments nsing 16 and 20 spring-calved Ayrshire cows in 1970 and 1971, respectively. A sward of S23 perennial ryegrass was used, and an average of 342 kg N/ha (305 lb N/ ac) was applied per annum. The paddock system had 28 separate paddocks; one paddock was grazed each day in rotation and occasionally topped in mid-season. The Wye College system had 4 plots of equal size and the cows were offered 1/7 of one plot each day; no back fence was used and surplus herbage was neither cut nor topped. The stocking rate on hoth systems was 1 cow per 0.20 ha (0.49 ac) in 1970 and per 0.16 ha (0.40 ac) in 1971. The mean daily milk yields per cow on the paddock and the Wye College systems were 16.2 and 15.3 kg (35.7 and 33.7 lb), respectively, in 1970; and 18.1 and 18.4 kg (39.9 and 40.6 lb) in 1971. The average annual output of milk was 13,500 and 13,150 kg/ha (1200 and 1170 gal/ac) on the paddock and Wye College systems, respectively. The fat and solids-not-fat (S.N.F.) contents of the milk were not significantly affected by the grazing system. It is concluded that the Wye College system was as effective as the paddock system in producing a high output of mUk per ha, but at a lower cost and with far fewer management decisions.     

A quick microtechnique for inspection of potato periderm or wound periderm formation

Summary A method for a quick inspection of wound periderm formation is described. Sections are freehand cut into a stain solution, and microscopic examination is accomplished with an epiplanatic lens.     

Laser fluorometric determination of aflatoxin B1 in corn.

A 2-step chromatographic separation, using both thin layer chromatography (TLC) and high pressure liquid chromatography (HPLC), in conjunction with the high sensitivity of laser fluorometry permits extension of the detection limits of aflatoxin contamination in corn to 0.1 ppb (microgram/kg) with a 26% root mean square variation. Aflatoxin B1 is extracted from corn with water-methanol and cleaned up by TLC. The recovery of aflatoxin from the TLC plates was linear from 10 to 1000 pg. Aflatoxin B1 is converted to the more highly fluorescent B2A derivative by treatment with 1N HCl. Experiments with aflatoxin B1 standard establish a constant conversion to B2A over approximately 3 orders of magnitude in B1 concentration. An extract of the B2A aflatoxin derivative is injected onto a reverse phase HPLC column. A flowing droplet of eluant is irradiated by an amplitude-modulated 325 nm He-Cd ion laser beam, and fluorescence from the droplet is detected by a lock-in amplifier in phase with the laser modulation. Several chromatograms are presented that demonstrate the capability of this procedure for removing interfering components in the corn extract.     

Cycling of nitrogen by surface-casting earthworms in a pasture ecosystem

Production of surface casts and the removal of plant litter from the soil surface by earth-worms had similar seasonal variations, with maximum values in May and minimum values occurring in July and August. Seasonal variations in the total nitrogen (TN) and oxidizable carbon contents of casts were closely related to variations in litter production. The C:N ratio of casts (10.7) was consistently smaller than that of underlying soil material (15.0 and 14.2 for the 0–5 and 18–22 cm depths, respectively), which is probably due to the mineralization of plant-derived organic material during passage through earthworms and utilization of low C:N ratio litter. Seasonal changes in the amounts of inorganic N forms in casts showed a build-up of NH₄⁺N in the cooler winter months (July and August), attaining a maximum of 112 μg.g^?1. with a decrease in autumn (April and May) and early spring (September and October), reaching a minimum of 54 μg.g^?1. The opposite trend existed for seasonal variations in the NO₃^?-N content of the casts. Because only minor fluctuations in the amounts of N forms were obtained for underlying soil material during the casting period, the more dramatic changes observed in the casts could not be explained by soil variations. Seasonal variations in urease enzyme activity, associated with fluctuations in organic matter content, were more important than the effect of temperature on enzyme activity in accounting for seasonal variations in the NH₄⁺-N content of casts. It was calculated that 73% of the TN content of litter removed from the surface by earthworms was accumulated in casts, indicating both the importance of earthworms in incorporating litter N with soil material and the inefficiency of N digestion by earthworms.     

Soil and erosion features of the central plateau region of Tigrai,Ethiopia

The results of reconnaissance soil surveys covering 6,000 km² are used to describe the Central Plateau region, which lies at elevations of 2,000 to 2,800 m in northern Ethiopia. Landform and soil sequences on calcareous shales, dolerites and sandstones are described, in which the principal soil units are Lithosols, Luvisols, Cambisols, Arenosols and Vertisols. Detailed morphological and analytical data are presented for a profile representative of arable soils in each sequence.Small-scale subsistence cultivation of cereals is the dominant land use; all land which is physically cultivable is at present cultivated. Settlement patterns are closely related to soil type, nucleated settlement occurring on fine textured soils but dispersed settlement on coarser textured and more freely draining soils.Erosion and soil moisture features of the three landforms described were investigated and compared. Empirical methods and suspended sediment measurements indicate high rates of regional soil loss (17–33 t ha^?1 yr^?1), accounted for by seasonally high rates of rainfall erosivity, steep terrain and poor land use. The recent development of gully erosion is seen to be linked to the disintegration of waterfall tufas. Application of the universal soil loss equation to arable lands indicates potential annual soil losses in the range of 400 t ha^?1 on Vertisols to 200 t ha^?1 on Cambisols: differences in rates are ascribed principally to differences in crop planting dates, which affect the degree of vegetative protection during periods of high rainfall erosivity.Soil moisture is shown to be in the available range for less than three months in the year. The time at which moisture in the profile enters the available range differed between the three soils monitored and was found to be closely related to the crop planting date, thus indirectly affecting the erosion hazard.     

Inoculation of pines with mycorrhizal fungi in natural soils—III: Effect of soil fumigation on rate of infection and response to inoculum density

Pinus radiata seedlings were inoculated with basidiospores of Rhizopogon roseolas and Suillus granulatus, and with chlamylospores of two unidentified but highly effective mycorrhizal fungi in undisturbed cores of natural soil fumigated with methyl bromide. Fumigation stimulated mycorrhizal infection rate and enhanced the response of seedlings to increasing concentrations of both inoculum types, but the effect of chlamydospore inoculum was more favoured by fumigation than that of basidio-spores. Chlamydospore inocula appear more sensitive to competitive and antagonistic soil microorganisms than basidiospores. Soil fumigation appears a necessary adjunct to the use of chlamydospores as inoculants in nurseries and is discussed in relation to nursery culture of pines.