EFFECTS OF ABOVEGROUND HERBIVORY ON SOIL MICROBIAL BIOMASS IN CONVENTIONAL AND NO-TILLAGE AGROECOSYSTEMS

The effects of above-ground herbivory on soil microbial biomass associated with maize (Zea mays) roots were measured in field experiments. Different grazing intensities were established by placing grasshoppers (0, 5, 10 and 20) in cages around individual maize plants, and allowing them to graze for 5 days. Soil samples were taken 12 days later at a depth of between 8 and 12 cm. Soil microbial biomass was measured using the chloroform fumigation direct extraction method. Results indicated that intermediate levels of herbivory increased soil microbial biomass in the no-tillage system. However, in a conventional tillage system no significant differences were found among the grazing treatments. It is hypothesized that increases in soil microbial biomass in the no-tillage system were attributable to increases in root exudates resulting from above-ground herbivory.