THE SIMULATION OF ANIMAL RETURNS IN GRASSLAND EXPERIMENTATION

An experiment was carried out on a grass/white-clover sward at North Wyke to evaluate the use of mixtures of inorganic and organic nutrient sources to simulate the nutrient effect of animal excreta, both with and without overall PK fertilizer. Grazing with sheep and the return of excreta from caged sheep both increased herbage yields, as did artificial return treatments. Artificial return treatments giving 75% of the nutrient level returned by excreta gave yields comparable with grazing. The effect of the simulated return treatments was not influenced by PK application. Grazing gave a very different botanical composition to that from the treatments in wbich natural or simulated excreta were returned to cut swards. Mixtures simulating excreta may replace the nutrient effect of the grazing animal, but not its physical effect, in some forms of grassland experimentation. They are not recommended for fertilizer trials.     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS

This paper describes the rate of growth of Italian ryegrass in the spring, measured by recording DM yield at weekly intervals up to 10 weeks. There were 3 levels of applied N: 25, 75 aud 125 lhJac (28, S4 and 140 kgJha). Rate of growth declined after the sixth week at all 3 levels of N. Grass receiving 25 Ib N produced 5000 Ib DMJac (5600 kgJha) in 10 weeks, that receiving 75 lb N 6800 Ib (7700 kgJha) and that receiving 125 lb N 7100 lb (8000 kgJha). The DM content of herbage fell after the first week and subsequently increased steadily up to 10 weeks; the fall was least marked and the rate of increase most rapid at tbe lowest level of N. In vitro digestibility (measured in one year only) was much affected by stage of growth and little affected by level of N.     

Survival of soil bacteria during prolonged desiccation

A determination was made of the kinds and numbers of bacteria surviving when two soils were maintained in the laboratory under dry conditions for more than half a year. Certain non-spore-forming bacteria were found to survive in the dry condition for long periods. A higher percentage of drought-tolerant than drought-sensitive bacteria was able to grow at low water activities. When they were grown in media with high salt concentrations, bacteria generally became more tolerant of prolonged drought and they persisted longer. The percent of cells in a bacterial population that remained viable when exposed to drought stress varied with the stage of growth.     

Oxygen inhibition of acetylene reduction (nitrogen fixation) in soil: Effect of glucose and oxygen concentrations

Sandy loam soil was amended with different concentrations of glucose and was incubated at different pO₂ levels. Under many conditions of incubation time and treatment, N₂ ase activity as determined by 1-h aerobic C₂H₂ reduction assay (flushed with Ar:O₂, 4:1 before assay) was significantly less than that determined by means of ambient assay (carried out at the pO₂ of incubation without flushing with Ar:O₂, 4:1 before assay). The difference between the N₂ase activity in aerobic assay and that in ambient assay increased with decreasing glucose and O₂ concentrations imposed during incubation. The inhition in aerobic assays was analogous to O₂-induced shut-off of N₂ase and amounted to 75 per cent inhibition after incubation at 0.06 atm pO₂ of samples amended with 0.75% glucose (w/w). Similar O₂ inhibition was observed after amendment with mannitol and with lactate. Times of incubation were chosen such that development of anaerobic N₂ase activity was either absent or too low to account for the observed effects of O₂ during assay. It was shown that 0.05 atm pC₂H₂ was adequate for routine 1-h assays of the soil system employed. Individual soil samples could be subjected to repeated 1-h assays (with removal of C₂H₂ and C₂H₄ by evacuation after each assay) thus avoiding side-effects of long exposure to C₂H₂.     

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.     

Characteristics and classification of three granite-derived soils in peninsular Thailand

The Phuket, Thung Wa and Huai Pong soils of this study form the Phuket catena and are extensive in Narathiwat province in the southern part of peninsular Thailand where they were studied in the field and sampled. The Phuket soils on the higher-lying positions and the Huai Pong soils on the nearly-level, lower positions, have developed argillic horizons and are Ultisols. The Thung Wa soils, which occur on intermediate positions and receive sediments from upslope, have cambic horizons and are classified as Inceptisols.All soils formed from Late Cretaceous or Early Tertiary granite or from sediments derived frome these granites under a tropical rain forest climate. They contain kaolinite as the predominant clay mineral and are highly leached, with base saturation of less than 35% in their B horizons. Cation exchange capacities are less than 6 mequiv. per 100 g soil and exchange acidity and exchangeable aluminium are high. Field and thin-section studies as well as particle-size analysis indicate considerable clay translocation from A to B horizons in the Phuket and Huai Pong soils and little clay movement in the Thung Wa soils.     

Some vegetation patterns in the Republic of the Sudan - a discussion

The distinction between vegetation arcs and vegetation patterns is discussed. Some patterns are distinguished which are the result of ancient dune-building processes. These occur on an ancient series of aeolian sands.     

Alpine disturbance studies: Olympic national park,USA

Measurements of downslope rock-creep, of the slow rate of plant establishment on alpine and subalpine road-cuts, and of the reduction in plant cover and plant production in two alpine plant communities, illustrate the degree of disturbance that can occur. The development of large trails or roads should not be permitted in areas of such active downslope rock movement, because of the natural rate of mass-wasting. If more people are to visit and enjoy the alpine communities, asphalt paths to confine their walking are desirable, for trampling experiments showed that plant cover and plant production were rapidly reduced in even one season of light use. Recovery during the following year was, however, quite rapid—especially in the snow-bank community. Different alpine and subalpine habitats have different sensitivities to disturbance, and any plans for increased human use must incorporate this kind of information.