Soil-landform relationships at two localities in Papua New Guinea

Two test areas, each of several hectares, in denudational terrain in the lowlands and highlands of Papua New Guinea were intensively studied to establish the association between soil conditions and landforms. Whether soils were allocated either to the great soil groups of a classification based on the 7th Approximation or to FAO soil units, an extremely wide range of soils occurred in each of the land units that could be distinguished on the basis of landform. Defensible statements concerning soil distribution were achieved only by limiting the categories of soil to the level of soil orders and by restricting the number of land units to three or four. Even so, the statistical significance of the relationships was very low.These results indicate that current techniques and sampling densities used in photointerpretative land resource surveys in terrains typical of Papua New Guinea can produce only very generalized information on soil distribution. To obtain reliable predictions of soil information at the level commonly implied in such surveys, further intensive studies on the relationships between attributes of soil, landform and vegetation are required.     

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.     

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.     

Carbon loss from roots of wheat cultivars

The amounts of organic materials released into soil from roots during the first 4 weeks of growth were determined for 11 cultivars of wheat (Triticum aestivum L.). Carbon loss from roots was measured by supplying ¹⁴CO₂ continuously to the shoots and measuring the ¹⁴C content of the roots, root-free soil, water-soluble material and CO₂ flushed from the root chamber. Six cultivars were compared in each of two experiments, with the cultivar Condor common to both experiments. There were no significant differences between cultivars, relative to Condor, for ¹⁴C activity present in soil, roots, water-soluble material or rhizosphere CO₂. There was a significant difference between cultivars in experiment 1, but not in experiment 2, for the variate log₁₀ (¹⁴C lost from roots: ¹⁴C translocated to roots).There was evidence that a reduction in growth temperature, within the range 10–15°C, increased carbon loss from wheat roots into the rhizosphere.     

The response of cylindrocladium conidia to soil fungistasis

Direct observation of washed conidia of Cylindrocladium scoparium on non-sterile soils, air dried and rewetted immediately before deposition of conidia, indicated that peak germination (33–58%) occurred after 24 h incubation at 26°C. Peak germination on continually moist soils was lower (18–26%) than on rewetted soils. Lysis of germ tubes and germinating conidia on continually moist soils at 26°C was evident with 48 h. Conidia did not germinate on continually moist soils at 6°C and lysis did not become apparent until 168 h. Conidia germinated at a high level (93–99%) in axenic culture in the absence of exogenous C and N sources. The inhibition of conidial germination on soils may be attributed, in part, to the presence of soil volatiles. Germination of conidia placed on washed agar disks and exposed to volatiles from four soils ranged from 51 to 86% of the no-soil controls. Addition of carbon (13 ng C per conidium as glucose) and nitrogen (65 pg N ng^?1 C as NH₄C1) nullified the inhibitory effect of the soil volatiles. Germinability assayed on a selective medium at 26°C of conidia in artificially infested soils (approximately 10⁴ conidia g^?1 soil) decreased progressively during incubation at 26°C from 1 week to 4 months. No germinable conidia were recovered from artificially infested soils after 2 months incubation at 6°C. Conidia of C. floridanum and C. crotalariae responded similarly to C. scoparium in many assays.     

Extraction,purification and properties of soil hydrolases

Invertase, cellulase, phosphatases, protease and β-glucosidase were extracted from permanent pasture soil with 0.2 M phosphate buffer (pH 8) in the presence of 0.2 M EDTA. This extract was further treated with ammonium and salmine sulphates. Attempts were made to fractionate these enzyme activities by gel and anion-exchange chromatography. Specific activities were estimated in all fractions and some characteristics of the purified enzymes (optimum pH, temperature and substrate concentration, and K_m and V_max) were investigated. The results indicated that extracted enzyme activities occurred partly in soil as a carbohydrate-enzyme complex and partly as a humo-carbohydrate complex.     

Microbial populations in pullman clay loam receiving large applications of cattle feedlot waste

One way to disperse waste from large commercial feedlots is to spread large amounts of the waste on limited areas nearby. The effects of this practice on the soil microbial populations was assessed. Feedlot waste (FLW) was applied for 5 yr at rates of 0, 22, 67, 134, and 269 t ha^?1 yr^?1. Additional treatments were 538 t ha^?1 yr^?1 for 1 and 3 years and applications of N and NPK fertilizer. Soil cores from plots were sampled for microbial analysis before, during, and after the fifth growing season. April, July. and December soil samples were analyzed to 180-, 20-, and 480-cm depths, respectively. The following utritional and physiological groups of microorganisms were counted: soil fungi on Rose Bengal agar; bacteria on a basal mineral salts medium, on nutrient agar (both aerobically and in BBL GasPak jars), and on EMB agar (Escherichia coli-type colonies and total counts); and nitrifying and denitrifying organisms. Little effect due to FLW application rates was found, and organisms producing coliform-type colonies on EMB agar did not persist in the soil. The results indicated that applying large amounts of feedlot waste will not deleteriously affect soil microorganisms.