Soil compaction under sugar cane (Saccharum hybrid sp.) cropping and mechanization in Mauritius

Abstract

Farm machinery is increasingly used in sugar cane production in Mauritius and is expected to cause soil compaction. A study was undertaken to ascertain whether the five major cane-growing soil groups of Mauritius were being compacted as a result of sugar cane cropping and mechanized harvesting. Bulk density was measured in situ using the excavation method and stabilized infiltration rate was determined with the CSIRO disc per-meameter on pristine soils under native vegetation, manually harvested sugar cane soils and mechanically harvested sugar cane soils. Bulk density results were generally not significantly different between pristine soils and manually harvested soils or between manually harvested soils and mechanically harvested soils. The only exception was in the super-humid Latosolic Brown Forest soil, where bulk density was significantly higher in the manually harvested soil by up to 0.4 g cm- 3 compared to the pristine soil. The stabilized infiltration rate of the sub-humid Low Humic Latosol and Latosolic Reddish Prairie soils was significantly higher with manually harvested sugar cane under irrigated conditions compared to pristine conditions, increasing from about 100 mm h- 1 to more than 200 mm h- 1. The mechanically harvested soils had significantly lower stabilized infiltration rate than the manually harvested soils, a minimum value of 55 mm h- 1 being measured in the Humic Latosol. It appears that compaction is not serious enough to affect sugar cane yield, as the bulk density of the soils under sugar cane in Mauritius varies between 1.0 and 1.3 g cm- 3, still lower than the threshold values of 1.5 to 1.7 g cm- 3 that were determined for other countries. However, the threshold values applicable for Mauritius must be determined before any firm conclusion can be drawn. There is a greater risk of runoff and erosion under high intensity rainfall with mechanized harvesting, and management of sugar cane plantations should aim at reducing or alleviating topsoil compaction. It is therefore suggested that minimum tillage and controlled traffic are the two most appropriate strategies for reducing compaction in the sugar industry of Mauritius.