Chemical control of siam weed (Eupatorium odoratum linn.) in Pinus caribaea (mor) seedlings. *****(abstract does not reflect on title)********

Investigations on the rate of decomposition of litter of Senna siamea (Lam (formerly Cassia siamea Lam) Irwin and Berneby) and Leucaena leucocephala (Lam. De Wit) by fungi at Gambari Agro-forestry plot located within rain-forest zone of Nigeria was carried out from August 1990 to November 1992. Mycoflora evaluation of soil samples collected from 0-5cm and 5-10cm soil depths was conducted. Fungi species isolated were Penicillium pinophylum Hedge, Aspergillus flavus Link, Aspergillus niger Van Tiegh, Rhizopus viride (Pers exf. Fr.), Aspergillus melleus (Yukawa), Aspergillus sydowii (bain, Sartory Thom and Chruch) and Aspergillus ustus (Bainer) Thom and Chruch. Fungi population at 0.5cm depth under both L. leucocephala and S. siamea between August 1990 and November 1991 was 319.2 x 103 spres g-1 of soil and 298.7 x 103 spore g-1 of soil respectively. At 5-10cm depth under L. leucocephla during this same period 204.5 x 103 spore g-1 of soil was recorded while S.siamea had 195.7 x 103 spores g-1 of soil. There were significant differences (P < 0.01) in population of fungi species at the two soil depths at all sampling periods of which 0-5cm depths was always higher. However comparison of population of individual fungal species differed from depth to depth (P < 0.05) throughout the sampling period under the two tree species. The litter decomposition rates of the two tree species were similar for the sampling periods of 1991 and 1992. average weight loss of L. leucocephala litters was 6% while S. siamea averaged about 5% between November 1990 and February 1991. litter weight loss between February 1991 to May 1991 was 54% for L. leucocephala and 44% for S. siamea. From May to August 1991, the average loss of weight litter was 70% for L leucocephala and 68.2% for S. siamea. For August to November 1991, average loss of weight of litter was 17.3% for L leucocephala and 14% loss for S. siamea. The trend was similar for the 1992 sampling period. Field and laboratory studies showed that moisture and temperature played significant role in amount of litter decomposed while the effect of pH was negligible. Seasonal variations in the availability of calcium, magnesium, potassium, sodium and nitrogen in the soil were observed during sampling periods. There was significant positive correlation between moisture availability, fungal population and nutrient availability under field and laboratory studies. In terms of nutrient availability under the plots of the two tree species the ranking took the order Ca>Mg>Na>K. organic matter at 0-5cm depth under S. siamea was significantly more than that of L leucocephala. However, at 5-10cm depth under L. leucocephala organic matter content was significantly higher than that found under S . siamea.