Volume 25, 73

Tropical Grasslands (1991) Volume 25, 73–84

Sustaining productive pastures in the tropics
1. Managing the soil resource

JOHN WILLIAMS and C.J. CHARTRES

Division of Soils, CSIRO, Canberra, ACT, Australia

Abstract

The grazing of pasture systems has many of the elements essential to a sustainable agro-ecosystem wherein the soil resource is not degraded through time. Unfortunately there is increasing evidence that the soils of Australian tropical grasslands are suffering serious and permanent degradation through our inability to manage grazing pressure under the highly variable climatic regime which characterises the Australian tropics.
This paper details the evidence of soil degradation under our current rangeland management and illustrates how far these practices are from that of a sustainable system. The challenge to find grazing systems that are sustainable is shown to lie in recognising that the soil-plant-animal ecosystem must be studied in an integrated way. Focus on short term animal productivity without consideration of the consequences to all other essential components of the ecosystem is shown to be a primary cause for degradation of the soil resource. Too often the consequences of a practice has not been considered because the components of the agricultural system have been studied in isolation.
Both salinity and soil acidification are identified as soil resource management issues that must receive attention in the Australian tropics. The use of tropical legumes, the clearing of woodlands, and the use of introduced grasses are all managements that can radically alter the flux of water, nutrient and salt in the soil profile. The management of these factors is the key to control of both salinity, and soil acidification. The place and balance of the grass, legume, shrub and tree is fundamental. Progress in building sustainable grazing systems in the tropics requires integrated ecological studies with increasing emphasis on both the role of soil biology in the cycling of nutrients and the movement of water and solute in the system.