SIZE AND ACTIVITY OF THE SOIL MICROBIAL BIOMASS IN THE ROW AND INTER-ROW OF A SUGARCANE FIELD UNDER BURNING AND GREEN CANE HARVESTING

The size and activity of the soil microbial biomass was studied in the plant row and in the inter-row of a sugarcane field under burning or green cane harvesting. The sites sampled were on the long-term trash management trial situated at Mount Edgecombe. Soils were sampled to 30 cm depth in (i) the centre of the plant row, (ii) 30 cm out from the row centre and (iii) 60 cm out from the row centre (i.e. the middle of the inter-row area). Under burning, the only substantial input of organic matter to the soil was from root turnover in the row area where the root biomass was concentrated. As a consequence, the size (microbial biomass C) and activity (basal respiration) of the soil microbial community were concentrated in the row. However, under green cane harvesting there was a large input of organic matter in the inter-row area in the form of the trash blanket itself and through turnover of crop roots that were concentrated in the surface 10 cm of soil below the trash blanket. As a result, soil microbial activity was considerably higher in the inter-row area under green cane harvesting than under burning. Such results highlight the benefit of green cane harvesting to soil quality under sugarcane production.