Review of existing knowledge on soil crusting in South Africa

Abstract

Soil crusting (surface sealing) is a widespread and serious problem throughout all nine provinces of South Africa and in neighboring countries, like Botswana, Namibia, Swaziland and Zimbabwe. It is a problem in extensive rangelands and game parks and under rain-fed cropping and irrigated agriculture. Both mineral and biological soil crusts are problems. Various research methodologies are used to study soil crusting. Soil factors determining the susceptibility of a soil to crusting include soil organic matter, sesquioxides, particle size distribution, exchangeable sodium percentage, magnesium: calcium ratio and parent material. Negative impacts of soil crusting include reduction of water infiltration, leading to increased runoff and erosion and induced drought; inhibiting soil aeration; inhibiting germination and seedling emergence; inhibiting root functioning and development. Management practices that lead to the development of bare areas on crusted soils or those are aimed at deliberately maintaining bare areas, e.g., under drip and micro irrigation, aggravate soil crusting and its negative impacts. Crusted soils often do not recover even after several decades. Soil crusts can be ameliorated by means of mulching or application of gypsum (or phosphogypsum) or organic soil conditioners, such as polyacrylamide.