CHANGES IN ORGANIC MATTER STATUS AND THE SIZE AND DIVERSITY OF THE SOIL MICROBIAL COMMUNITY WITHIN A SUGARCANE FIELD

摘要

This study was initiated to investigate how soil organic matter status changes within a sugarcane field. The concentrations of organic C, labile organic fractions, and the size and activity of the microbial community were measured to a depth of 30 cm below the plant row and at distances of 30 and 60 cm into the inter-row area under pre-harvest burning or green cane harvesting with retention of trash residue as mulch. Total root mass was similar under burning and trashing but, under trashing, there was a redistribution of roots towards the surface 0-10 cm in the inter-row space as roots proliferated beneath the trash mulch. Soil organic C content decreased in response to both increasing distance from the plant row (to a depth of 20 cm) and burning rather than trashing (to a depth of 10 cm). Declines in soluble C, light fraction C, microbial biomass C, basal respiration and aggregate stability in response to distance and burning were much more marked than those for organic C and occurred to a depth of 30 cm. Heterotrophic functional diversity of the microbial community was also investigated. Principal component analysis of the response curves showed that soils below the row and those under trashing at 30 cm out from the row were separated from the other soils. The soil microbial diversity was generally greater in the row than the inter-row and tended to be higher under trashing than burning. It was concluded that soil in the inter-row of burnt sugarcane receives few inputs of organic matter and that conversion to green cane harvesting with retention of a trash mulch greatly improves the organic matter, and microbial and physical status of the soil in the inter-row.