Abstract
Recently published results regarding South Africa’s cropping potential show that about one third of the arable land is of low potential, located mainly in semi-arid areas, with the main problem being water shortage. This is therefore an appropriate time to review priorities and procedures, for selecting benchmark ecotopes to represent marginal areas, and for research needs with regard to water conservation strategies to mitigate the problems of low yields. Relevant international principles encapsulated in the words agro-ecology, sustainability and socio-economic conditions, are discussed. Relevant new technologies are described, namely: digital soil mapping that will facilitate the identification of benchmark ecotopes; a stochastic procedure to predict rainfall intensity data from daily rainfall that will facilitate runoff predictions; a crop yield cumulative probability procedure that enables sustainability to be described quantitatively. As a case study, results from a successful field experiment using the infield rainwater harvesting production technique on benchmark ecotopes in a semi-arid area, inhabited by subsistence farmers, are presented. The objectives of the study, procedures used and the method of expressing the results are recommended as guidelines for contributing towards mitigating the problem of low crop productivity across a large portion of the arable area in South Africa.
Highlights
The recently published results regarding the cropping potential of South Africa (Le Roux et al, 2016) show that at least one third of the arable land is of low potential
Le Roux et al (2016 p. 83) recommend that ‘detailed assessment of the 15 m ha occupied by subsistence farmers needs to receive the highest priority’. This priority is intimated in the following statement by Paterson et al (2015 p. 6): ‘The challenges begin with the need for recognition of the future central role to be played by the Natural Agricultural Resource Information System towards food security, environmental sustainability and the nation’s social well-being.’
Considering the current land evaluation needs in South Africa leads to the logical conclusion that the most important current objective needs to be the identification and evaluation of ecotopes that are representative of the cropping areas of low potential, and especially those in areas occupied by subsistence farmers
Summary
The recently published results regarding the cropping potential of South Africa (Le Roux et al, 2016) show that at least one third of the arable land is of low potential. Considering the current land evaluation needs in South Africa leads to the logical conclusion that the most important current objective needs to be the identification and evaluation of ecotopes that are representative of the cropping areas of low potential, and especially those in areas occupied by subsistence farmers These ecotopes will be described as benchmark ecotopes, equivalent to the term ‘benchmark sites’ used by Uehara and Tsuji (1990) for their international project titled ‘International Benchmark Sites Network for Agro-technology Transfer (IBSNAT)’, and as used in the following Water. The provisional procedure for identifying ecotopes using land type survey (LTS) data in the form of climate-soil-slope units, described by Schoeman and MacVicar (1978), was a valuable first approximation that served a useful purpose Because it did not involve actual measurements, it was subjective in nature and could have resulted in considerable errors. Considering the future need to evaluate the productivity of many marginal benchmark ecotopes in semi-arid areas, if the use of the combination of the two models described above proves to be consistently reliable, this strategy offers a useful means of estimating the yield benefits obtainable with the in-field rainwater harvesting (IRWH) production technique before conducting expensive field experiments on an unnecessary number of benchmark ecotopes
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