Abstract
This review provides an overview of Water Research Commission (WRC)-funded research over the past 36 years. A total of 28 WRC reports have been consulted, 13 of these compiled by the University of the Free State, 4 by the University of Fort Hare, and the remainder mainly by the ARC-Institute for Soil Climate and Water. This work has resulted in extensive capacity building in this field – numerous technical assistants and 58 researchers have been involved, of which 23 are still active in research.The focus on the water flow processes in the soil-plant-atmosphere continuum (SPAC), with particular emphasis on processes in the soil, has greatly enhanced understanding of the system, thereby enabling the formulation of a quantitative model relating the water supply from a layered soil profile to water demand; the formulation of logical quantitative definitions for crop-ecotope specific upper and lower limits of available water; the identification of the harmful rootzone development effects of compacted layers in fine sandy soils caused by cultivation, and amelioration procedures to prevent these effects; and management strategies to combat excessive water losses by deep drainage. The explanation of the way in which SPAC is expressed in the landscape in the form of the ecotope has been beneficial with regard to the extrapolation of studies on particular SPACs to the large number of ecotopes where detailed studies have not been possible. Valuable results are reported regarding rainfall and runoff management strategies. Longer fallow periods and deficit irrigation on certain crop ecotopes improved rainfall use efficiency. On semi-arid ecotopes with high-drought-risk clay and duplex soils and high runoff losses, in-field rainwater harvesting (IRWH), designed specifically for subsistence farmers, resulted in maize and sunflower yield increases of between 30% and 50% compared to yields obtained with conventional tillage. An indication of the level of understanding of the relevant processes that has been achieved is demonstrated by their quantitative description in mathematical and empirical models: BEWAB for irrigation, SWAMP mainly for dryland cropping, and CYP-SA for IRWH. Five important related research and development needs are identified. The WRC has played, and continues to play, an important role in commissioning and funding research on water utilisation in agriculture and has clearly made an excellent contribution to the progress made in addressing the needs and requirements of subsistence, emergent and dryland farmers in South Africa.Keywords: BEWAB, SWAMP, CYP-SA, in-field rainwater harvesting, dryland ecotope, irrigation
Highlights
This paper is presented in 3 main parts
On semi-arid ecotopes with high-droughtrisk clay and duplex soils and high runoff losses, in-field rainwater harvesting (IRWH), designed for subsistence farmers, resulted in maize and sunflower yield increases of between 30% and 50% compared to yields obtained with conventional tillage
The motivation forms the first part of the introduction and explains the importance of the subject, not just for South Africa and for all parts of the world where food production under semi-arid conditions is difficult
Summary
This paper is presented in 3 main parts. The overall aim envisages much more than just paying tribute to the excellent work done by many diligent agricultural scientists and their assistants over a period of 36 years, as well as the associated foresight of the Water Research Commission (WRC) in commissioning these projects and providing funding for these research teams. The motivation forms the first part of the introduction and explains the importance of the subject, not just for South Africa and for all parts of the world where food production under semi-arid conditions is difficult. In the second part of the paper the soil-plant-atmosphere continuum (SPAC) is defined, together with, firstly, the problems associated with promoting the water use efficiency of the system, and secondly, details about efforts to deal with these problems by agricultural scientists of many disciplines. The overall aim envisages much more than just paying tribute to the excellent work done by many diligent agricultural scientists and their assistants over a period of 36 years, as well as the associated foresight of the Water Research Commission (WRC) in commissioning these projects and providing funding for these research teams. ‘Quantifying the water flow processes in SPAC’, and ‘Managing rainfall and runoff’, is to focus on past research results that serve as signposts for the way ahead. These are considered to be the high-priority aspects that need diligent attention to ensure sufficient food production for an ever-growing population, putting further strain on a natural resource that does not increase in size, and could even decrease drastically in size if not properly cared for
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