Phosphorus mobilization from sugarcane soils in the tropical environment of Mauritius under simulated rainfall

Abstract

The continuous application of phosphorus (P) to agricultural systems to ensure profitable crop productivity can lead to an accumulation of P in agricultural soils. While this long-term residual pool of soil P is desirable from an agronomic perspective, there is some concern about its possible impacts on surface water quality as it may lead to eutrophication. Since a better understanding of P transport processes provides useful information for the development of site-specific P management strategies, rainfall simulation studies (100 mm h−1 for 30 min) on runoff plots (2.1 m × 0.75 m) were conducted at 20 field sites to study the mobilisation of soil P from sugarcane fields of Mauritius. The research findings indicated that the edge-of-plot P losses were insignificant from an agronomic perspective but only small amounts of P can actually trigger eutrophication in freshwaters. The results also showed that total P concentrations in runoff are more strongly associated with runoff sediments (r2 = 0.92) than runoff volume (r2 = 0.49) indicating that a greater proportion of the P transported in runoff occurred as particulate P rather than dissolved P. Actually, about 89 % of total P loss in runoff waters was mobilised in particulate form, pointing to the importance of erosion as a mechanism for mobilising soil P. The research findings suggest that in addition to the current management practices aiming at reducing runoff volume, such as conservation tillage and trash cover, measures that reduce sediments in runoff, such as grassed waterways and riparian buffers, may further attenuate P losses.