Soil aggregate properties and total available water as affected by sugar cane (Saccharum hybrid sp.) production in Mauritius

Abstract

Concerns within the sugar industry of Mauritius with respect to soil degradation caused by sugar cane cropping have led to a study on soil quality. As part of this study, the effects of sugar cane production, i.e. cropping and adoption of mechanized practices, on aggregate size distribution, aggregate stability and total available water were investigated for the five major soil groups of Mauritius. These three parameters are indicative of the status of soil structure. Aggregate size distribution was determined by dry sieving, aggregate stability was derived from soil moisture characteristic curves of weathered and unweathered soil samples, and total available water was determined using ceramic pressure plate and cellulose membrane techniques. The results showed that, in general, neither soil structure nor total available water were degraded following the introduction of the sugar cane crop and the subsequent implementation of mechanized practices. A significant increase in aggregate size was observed with cropping in a rocky soil from the sub-humid zone, possibly because of changes in rooting density, with higher biomass being produced under irrigated conditions. On the other hand, aggregates were smaller in soils from the humid to super-humid zones, probably because of a lower organic matter content. Adoption of mechanized practices could also have impacted positively on aggregate properties through soil consolidation under harvester traffic. Aggregate stability decreased significantly with the adoption of mechanized practices only in the Low Humic Latosol, which has the lowest natural organic matter content. In this case, organic matter content could have been depleted with cropping below a critical threshold level. No significant difference was observed in terms of total available water. It can be concluded that sugar cane cropping has not degraded soil structure in the major soils of Mauritius but care should be taken to minimize organic matter depletion when adopting mechanized practices in the Low Humic Latosol.