WEED DENSITY AND SPECIES COMPOSITION AFTER TWO YEARS OF SOIL FERTILITY MANAGEMENT IN AN ORGANIC CITRUS ORCHARD

Field experiment was conducted in a citrus orchard at the National Horticultural Research Institute, Ibadan, to assess weed composition and cover on plots receiving various organic, in-organic and organo-mineral fertilizers. These fertilizer sources were applied at 0.45tha-1 N.P.K., 10tha-1 poultry manure (P.M), 10tha-1 P.M. + 0.2tha-1 N.P.K., 15tha-1 P.M., 15tha-1 P.M + 0.15tha-1 N.P.K., 20tha-1 P.M. and No fertilizer (control). Results indicated that plot with fertilizer treatment 0.45tha-1 N.P.K. recorded the highest weed density of 40plants/m2, weed fresh weight of 425g/m2, weed dry rate of 78g/m2 and species composition of 15%, these were significantly higher than other fertilizer treatments. Least weed density of 20.3plants/m2 was obtained from plot that received no fertilizer i.e, control, while least weed fresh and dry weight of 215g/m2 and 56.3g/m2 respectively were obtained from plot that received fertilizer treatment 15tha-1 P.M + 0.15tha-1 N.P.K. and these were significantly lower compared with other fertilizer treatments. The highest weed dominance index value of 0.41 was obtained from plot that received 15tha-1 P.M. + 0.15tha-1 N.P.K. indicating less evenly distribution and high dominance of weed species, plot treated with 10tha-1 P.M. recorded the highest percentage ground coverage of 24% while Ageratum conyzoides recorded the highest importance value of 20. The greater the importance value, the more competitive is the weed and weed management required. Improvements in the fertility of nutrient-poor soils of the tropics might increase weed pressure and make the development of effective weed management strategies more critical.