Influence of Sugarcane Cropping on Organic Matter and Microbial Biomass Contents of Rock-Free and Rocky Soils in Two Contrasting Agro-Climatic Zones of Mauritius

Marked differences exist in the properties of the major soil groups of Mauritius on account of differences in age of parent material and in climatic conditions under which these soils have developed. Further differences are expected to be observed in their organic matter and microbial biomass contents as a result of sugarcane cropping. A study was conducted on the four major soil groups of Mauritius to quantify and compare these effects. Organic carbon, total nitrogen and microbial biomass carbon contents were measured for uncropped and cropped conditions. The results showed that soils of Mauritius have average organic carbon and total nitrogen contents of about 100 and 9.5 T/ha for the upper 50 cm layer, and 500 kg/ha of microbial biomass carbon for the upper 15 cm layer. Cropping with sugarcane had variable effects on these three parameters, but did not necessarily cause their degradation. Differences observed could be explained by differences in agronomic practices, as a consequence of differences in rainfall regimes and rock contents. These different agronomic practices include rock-removal for mechanization, cane burning for harvest and addition of organic amendments.