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Agricultural land use and sugarcane residue management effects on soil bacterial communities at two long-term sites in KwaZulu/Natal, South Africa, were investigated by PCR-DGGE. Land uses at site 1 were maize [M]; pre-harvest burnt sugarcane [SC]; permanent kikuyu pasture [KIK]; pine forest [PF]; wattle forest [W] and undisturbed native grassland [NAT], whereas land managements at site 2 were pre-harvest burning of sugarcane [Bto] or green cane harvesting with retention of a trash mulch [T] (with [F] or without [Fo] fertilizer additions). At site 1, non-metric multidimensional scaling (NMS) separated all land uses, indicating variation in species composition between sites. Species richness and diversity but not evenness differed between land uses. Canonical correspondence analysis (CCA) showed that soil properties (extractable P, acidity, Mg, total cations, K and organic C) were significantly related to bacterial community composition. At site 2, NMS indicated large differences in soil bacterial community composition under trashing versus pre-harvest burning. Species richness was significantly different between treatments but not evenness or diversity. CCA indicated organic C was the main factor associated with the trashing/burning effect and exchangeable Mg with the fertilizer effect, on bacterial communities. Long-term differences in land use or soil management within a single soil type and location thus induced substantial differences in bacterial community composition.
