Sugar cane has been grown in Mauritius for over 350 years in a monocropping system. As a result, soil quality could have declined since productivity has been stagnating over the last twenty years in spite of improved agronomic practices and higher-yielding varieties. A study was therefore initiated to determine the effects of sugar cane production practices on the biological quality of the major soil groups of Mauritius. Organic matter (OM) and microbial biomass contents were determined for soils with different cropping histories, namely native vegetation, cropping with sugar cane under manual conditions, and cropping with sugar cane under mechanized conditions. When virgin soil was compared to manually-cropped soil, OM content was found to decrease with cropping in the topsoil, but to increase in the subsoil as a result of soil mixing through tillage. Microbial biomass also decreased in the topsoil as the microbial population had less OM to feed on. When manually-cropped soil was compared to mechanically-cropped soil, both OM and microbial biomass tended to decrease with mechanization as the soil was highly disrupted following land preparation. This decline in soil biological quality will continue if remedial measures are not taken, the latter being trash blanketing, addition of substantial amounts of organic wastes, and the incorporation of leguminous green manures within the cropping cycle, among others.
This chapter is the concluding part of a book containing a series of research studies and state-of-knowledge review chapters that illustrate the range of drivers of land-use change in the tropics and the ways in which these are affecting soils. The contributions in the book are from all continents where tropical and savannah environments are found and from authors across the world. Contributions have been grouped into three broad areas covering: soil microbial populations and processes; urban soils, agriculture and soil contamination; and soil carbon (C) and soil organic matter (SOM). Although the book do not cover all the factors and processes affecting soils in the tropics, emergence of key themes that can be used to inform future research directions were identified. To conclude, a synthesis was produced that draws on findings from each of the chapters and includes the thoughts of many of the authors on the main challenges ahead for a sustainable future for tropical and savannah soils. These are based around where and how sampling should be conducted and analysed; adopting a holistic approach to understanding soil functioning and fertility; utilizing new molecular techniques to test hypotheses relating to soil processes and the impacts of land-use change; and, finally, reconciling the multiple demands on soils in rural and urban settings. Further, the Global Soil Partnership have set out 'Five Pillars of Action' that are summarized here as a guide to the way forward: (1) promote sustainable management of soil resources for soil protection, conservation and sustainable productivity; (2) encourage investment, technical cooperation, policy, education, awareness and extension in soil; (3) promote targeted soil research and development focusing on identified gaps, priorities and synergies with related productive, environmental and social development actions; (4) enhance the quantity and quality of soil data through improved data generation, analysis, validation, reporting, monitoring and integration with other disciplines; and (5) harmonize methods, measurements and indicators for the sustainable management and protection of soil resources.
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