This study compared the properties of conventionally managed sugarcane soils (sugarcane monoculture,
extensive tillage during the replanting operation, random traffic from harvest machinery and crop
residues sometimes burnt) with soils under a new sugarcane farming system based on crop rotation,
minimum tillage, controlled traffic and residue retention. Soils under perennial pasture were included as
a standard reference. Adjacent fields under the three land management practices (new sugarcane, conventional
sugarcane and pasture) were sampled at 11 sites in tropical and sub-tropical Australia and a
range of soil properties were measured (texture, soil chemical parameters, enzyme activity, composition
of the nematode community, catabolism of C sources using Biolog Ecoplates®). For most parameters, differences
between soils under the new and conventional sugarcane farming system were not significant.
Pasture soils were markedly different. They had nearly twice as much total C, total N, permanganateoxidisable
C and water-soluble C as cropped soils and this impacted on their biochemical and biological
status. Thus cellulase activity and microbial activity (measured as the rate of degradation of fluorescein
diacetate) were respectively five and two times higher in pasture soils than in soils cropped to sugarcane.
Analysis of nematode assemblages indicated that total numbers of free-living nematodes and the
ratio of free-living to plant-parasitic nematodes were higher in pasture than sugarcane soils and that
fungal-feeding nematodes were more predominant under pasture than sugarcane. These results indicate
that the biological status of sugarcane soils is poor relative to soils under permanent grass pasture.
However, sugarcane soils managed under the new farming system for 5–7 years had a lower C/N ratio,
more free-living nematodes and a greater proportion of fungivorous to bacterivorous nematodes than
conventionally managed soils, indicating a shift towards the biological properties of pasture soils. Since
such improvements in the health of non-tilled sugarcane soils are likely to continue for many years, the
data obtained in this study will be a useful benchmark for future studies.