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.     

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.     

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.