BIOLOGICAL EFFECTS OF PLANT RESIDUES WITH CONTRASTING CHEMICAL-COMPOSITIONS UNDER HUMID TROPICAL CONDITIONS - EFFECTS ON SOIL FAUNA

Effects of application of five types of plant residues [Acioa barteri, Gliricidia sepium and Leucaena leucocephala prunings, maize (Zea mays ) stover and rice (Oryza sativa) straw] as mulch on soil fauna were ex amined under field conditions in the humid tropics in 1990 and 1991. E arthworm mean population over 2 years was higher under any type of pla nt residues by 41% compared to control. Leucaena prunings supported th e highest earthworm population. Mulched plots also showed 177% higher mean termite population over 2 years than control. Highest termite pop ulation was observed in plots mulched with Acioa prunings followed by maize stover > rice straw > Leucaena prunings > Gliricidia prunings. T he mean ant populations were 36% higher with Leucaena and Gliricidia p runings, and were not affected by Acioa prunings, maize stover and ric e straw as compared to control. Millipede populations were not signifi cantly affected by mulching. Earthworm populations were negatively cor related with the ratio of lignin: N of plant residues. Ant populations were significantly related to the N content of plant residues (R2 = 0 .87 and 0.84 for 1990 and 1991 respectively). The results imply that c hemical plant composition, particularly N and lignin contents, play a critical role in faunal abundance in the soil through their effect on palatability and decomposibility. Indirect microclimatic and mulching effects may also be important.