Effects of sugar cane (Saccharum hybrid sp.) cropping on soil acidity and exchangeable base status in Mauritius

Abstract

Continuous sugar cane cropping commonly leads to soil acidification. Such an effect can be attributed to N fertilization and to leaching and removal of exchangeable bases. A study was conducted on the five zonal soils of Mauritius to ascertain whether continuous sugar cane cropping was causing the soil pH and level of exchangeable bases to decline to such an extent that it would threaten the sustainability of the island’s sugar industry. Soil pH, K, Ca and Mg concentration were determined for samples that had either been under native vegetation or cropped with sugar cane. Cropping was beneficial to pH in the sub-humid Low Humic Latosol (L) and Latosolic Reddish Prairie (P) and humid Humic Latosol (H) soils, but detrimental in the super-humid Humic Ferruginous Latosol (F) soil. The increased pH in the first three soils was caused by the regular application of pH-enhancing amendments such as lime, coral sand, filter mud and poultry litter. In the F soil, the acidification of the topsoil was accompanied by a pH increase in the subsoil, indicating that bases had been leached down the profile by rainfall. Cropping was not detrimental to exchangeable base status, indicating that current applications of K, Ca and Mg-containing compounds to the sugar cane crop were also generally adequate to compensate for the removal and losses of these elements. Since sugar cane cropping does not lower soil pH or reduce levels of exchangeable bases, it can be concluded that current recommendations with respect to liming and exchangeable base application are adequate for the long-term sustainability of the sugar industry and should be adhered to.