EFFECT OF MULCH QUALITY ON EARTHWORM ACTIVITY AND NUTRIENT SUPPLY IN THE HUMID TROPICS

An experiment was conducted in 1990 and 1991 at the International Inst itute of Tropical Agriculture (IITA), Ibadan, Nigeria to study the rol e of earthworms in the decomposition of plant residue mulches with dif ferent qualities. Five mulches of Dactyladenia barteri, Gliricidia sep ium, Leucaena leucocephala prunings, maize (Zea mays) stover and rice (Oryza sativa) straw, which had a wide range of C-to-N ratio, lignin a nd polyphenol concentrations were studied. Based on their chemical com positions, Dactyladenia prunings were defined as low-quality mulch, Le ucaena and Gliricidia prunings as high quality-mulches, and maize stov er and rice straw as intermediate-quality mulches. The mean density of earthworms (Hyperiodrilus africanus and Eudrilus eugeniae) in the exp erimental plots decreased in the following order: high quality > inter mediate quality > low quality mulches. High quality mulch (Leucaena an d Gliricidia prunings) supported 54% higher earthworm populations than the (no mulch) control, whereas low-quality mulch (Dactyladenia pruni ngs) only increased earthworm density by 15%, compared to the control in 1990. Plots with Leucaena and Gliricidia prunings had the highest e arthworm populations at the initial stage of the experiment, while the other treatments showed increased earthworm numbers at a later stage. Effects of earthworms on mulch decomposition were examined in the fie ld in large pots with or without earthworms (Eudrilus eugeniae). The e ffects of earthworms were more pronounced for Dactyladenia prunings (l ow quality), than for Leucaena and Gliricidia prunings (high quality). The results indicate that manipulation of earthworm activity with app lication of high- and low-quality mulches may improve the synchronizat ion of soil nutrient supply and crop nutrient demand. (C) 1997 Elsevie r Science Ltd.