Thesis (BS Biology) -- University of the Philippines Mindanao, 2011

To compare the effects of manual and chemical weeding (using paraquata and glyphosate), and determine othe rfactos that may affect earthworm populations in a banana planation, a long term field experiment was conducted in two sites (15% and 25% slope). The field experiment was supplemented by an avoidance test and reproduction test using paraquat and glyphosate. and Pontoscolex corethrurus as the test species. Based on four years of field observation, there was no significant difference in earthworm count between manual and chemical plots (15% slope: F-ratio:0.96, P=0.43; 25% slope: F-ratio:14.18, P=0.06). The earthworm species composition was found t differ between the two sites. The 15% site tends to have a higher soil organic matter content. Earthworms populations were on a declining trend in both treatments for both sites, but regression analyses show these trends to be insignificant. Rainfall, organic mulch and weed cover were not significantly correlated with the earthworm counts. However, the declining pH in both sites could help explain the decline in earthworm populations. P. corethrurus showed significant avoidance response to normal concentrations glyphosate (P=0.03) but not to paraquat (P=0.55). The reproduction test failed to show significant effects of paraquat and glyphosate, up to 16x the normal rate, to earthworm survival, growth and reproduction. The experiments suggest that both weed management treatments do not pose a significant threat to earthworms under the conditions studied. The negative effect of declining pH needs further study