Department of Agronomy

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Browsing Department of Agronomy by browse.metadata.advisor "De Vries, Sander"

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    Quantifying yield gaps for rain-fed maize (Zea Mays) in South Africa: A bottom-up approach
    (Stellenbosch : Stellenbosch University, 2018-03) Mandigora, Brian George; Le Roux, Marcellous; De Vries, Sander; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Maize (Zea mays) is an important crop that supports livelihoods in South Africa (RSA) and most of the Sub-Saharan Africa (SSA) region. Currently, RSA is the biggest maize producer in the region, exporting to countries like Zimbabwe, Botswana and Malawi. However, the anticipated increase of the world population to 9 billion people by 2050 presents new challenges for resource supply and management, including food supply. The bulk of this population increase is expected to occur in the SSA region, and feeding this bigger population without compromising land and water for other needs is a priority. This thesis presents a yield gap study that seeks to ascertain the levels to which South African yellow and white maize yields can be increased on more or less the same spatial scale by applying the Global Yield Gap and Water Productivity Atlas (GYGA) protocol. The South African maize producing regions were subdivided into five key agro-climatic zones, referred to as designated climate zones (DCZs), which are explained by the GYGA Extrapolation Domain (GYGA-ED) zonation scheme. Within these DCZs, eight Reference Weather Stations (RWS) were selected to represent the South African maize production zones. Using Geographic Information Systems (GIS), buffer zones of 100km radius were delineated around the RWS, and were clipped according to CZs to avoid overlap. Climatic, edaphic and crop management data were collected for each of the RWS buffer zones. These data were used to simulate water-limited potential yields (Yw) for yellow and white maize for the three main soil types within the buffer zone under specific crop management practices from 2000 to 2014. Data for actual yields achieved by farmers during the same 15-year period (Ya) were sourced from the GrainSA database, and was corrected for moisture content. The Hybrid-Maize model was used to simulate Yw for yellow and white maize for the period from 2000 to 2014. The national yield gap (Yg) was calculated as the difference between the weighted values of Yw and Ya (Yg = Yw – Ya). The relative yield percentage (Y%) was also calculated as Y% = Ya/Yw x 100. This study found that for South Africa, the yield gaps between average farmers’ yields and simulated water limited potential yields were 2.70 tha-1 for yellow maize and 3.14 tha-1 for white maize, which represent 52.99% and 57.88% of the white and yellow maize yields, respectively that are achievable as simulated by Hybrid-Maize. The exploitable yield gap (Ye), which is calculated as Ye = 0.8Yw – Ya, is the yield that can realistically be achieved by farmers when economic and bio-physical limitations are considered. If the Ye is to be met by South African maize farmers, this would increase annual production by about 1.5 million tonnes (yellow maize) and 3 million tonnes (white maize), which indicate a total maize yield increase of 42%, translating to over R9 billion in additional gross income for farmers. Therefore, there is considerable potential for RSA to increase maize production on existing farmland using current crop management practices, which could provide national and regional food security.