SOILCOMPACTION: THE EFFECT OF GRAIN SIZE DISTRIBUTION
GOH HOCK SWEE
SUMMARY
Soil samples and soil clods were collected from eleven sites in Eastern Oregon. Their grain size distributions were determined.The soil samples were equilibrated to three matric suctions, and compacted by a series of staticpressure. Semilog graphs of bulk density versus pressure obtained were linear over the range of applied stress and moisture content of the experiment. The slopes of the graphs with different moisture content the same soils were parallel to each other. This indicates that the slopes of the graphs and the compression index are independent of the moisture content. The minimum static stresses required to produce the clod bulk densities found in the field were estimated in the laboratory. The limitations of this calculation are discussed. A multiple regression ofthe dependent variable, bulk densities on the independent variables of grain size and organic matter was carried out. Fine silt content together with total sand accounted for 90% of the variation in bulk density.
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RODENT PEST SPECIES AND BAIT PREFERENCES IN COCOA-COCONUTP LANTINGS
C.H. LEE
SUMMARY
Studies on rodent pest species composition, sex distribution and bait preferences were carried out in cocoa plantings intercropped with coconuts. Laboratory studies on the damage potential of each rat species were also undertaken. Six rodent species were identified to be present in the areas. R. tiomanicus, and C. notatus were the dominant species. Equal numbers of male and female rats were trapped, however a higher proportion of squirrels were females. Bananas and burnt copra were the most preferred baits. Studies indicated that C. gliroides = R. tiomanicus> R. argentiventel> R. rattus diardii> R. exulans respectively in order of their damage potential. The study also showed that traps could be used to reduce pest numbers effectively.
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POPULATION MODEL OF THE BROWN PLANTHOPPER, NILAPARVATA LEGENS (STAL.)
K.L. HEONG
SUMMARY
A population model of the brown planthopper (BPH), Nilaparvata lugens Stal. was developed. Simulation studies using data obtained from the literature, showed that the population trends predicted by the models resembled that observed in the field very closely. As the data were from the temperate regions, no attempts were made to directly compare the model outputs with those of the field. The effects of both a residual and non-residual insecticide were also studied through stimulations. Although the model developed would not be used immediately it did serve its important functions of identifying research priorities, providing a framework of the BPH population and coordinating research efforts. Uses and the roles the model can play in improving BPH pest control were also discussed.
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THE EFFECTS OF SUN AND OVEN-DRYING ON THE GERMINATION AND STORABILITY OF RICE (ORYZA SATIVA) SEEDS
TENG YEEW THAI and SHAHARUDDIN MOHD DAUD
SUMMARY
Sun-drying and oven-drying (40°C) were carried out on two rice varieties (Mahsuri and Pulut Malaysia I) to determine their effects on seed qulity in terms of seed germination and storability. Although sun-drying resulted in more rapid reduction in seed moisture, the final moisture content attained by the seeds was higher thant hat of the oven-dried seeds at the end of the eight-day drying period. There was no significant difference (P=0.05) in the germination of the sun-dried and oven-dried seeds during the drying period. The adverse effect of sun-drying became more evident during subsequent storage. This was shown by the more rapid deterioration of the sun-dried seeds especially under ambient conditions (28°-30°C; 80% RH).
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AN INVESTIGATION INTO THE GROWTH OF CANDIDA OBTUSA IN LIQUID PINEAPPLE WASTE
SUHAIMI, M., WEBB, B.H. and SUTANTO, J.B.
SUMMARY
An aerobic fermentation of liquid pineapple waste using Candida obtusa as the growing organism was carried out. In the continuous culture, aeration and dilution rates were varied. The COD concentration, agitation rate and culturing temperature were kept constant. With a COD concentration of about 90 g/l in the influent liquid, it was found that the amount of air supplied was still limiting. Low growth rates and inefficient utilisation of the organic substances present in the liquid waste was thus obtained. The yeast concentration could be increased with aeration rate. With a higher dilution rate, the yeast concentration decreased while the COD concentration increased. The calculated results for these two variables save a more favourable values.
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