Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Investigating the potential income and future water requirements of existing pecan orchards in the Western Cape

Auteur : Oberholzer, Abraham Stephan

Université de soutenance : Stellenbosch University

Grade : Master of Science (MScAgric) 2022

Résumé partiel
The peak in pecan production occurs between 12 and 15 years, in traditional densities of 10 x 10 m, resulting in a long period before break even. To address this financial challenge, different approaches can be followed i.e., higher planting densities and earlier production, and cultivar choice for higher productivity, nut quality and adaptability to the environment. Tree performance under higher densities were evaluated in newly established orchards varying from three to six years, with the objective to assess vegetative and reproductive development of ’Wichita’ pecans in the Hermon and Vredendal regions of the Western Cape, South Africa. Additionally, the suitability of three main cultivars, Wichita, Navaho and Choctaw, were evaluated in the Vredendal region. Both studies were conducted during two consecutive seasons. A desktop study on evapotranspiration was conducted using historical data (2009-2020) for both regions, applying the FAO-56 model in conjunction with a locally adapted pecan-specific model, to ascertain the potential water use of pecans under current and future climate scenarios. In paper 1, phenological development in Hermon commenced approximately two weeks earlier than in Vredendal. Results from both seasons and regions suggested that lower densities resulted in larger trees (volume), with no difference in light interception at this stage, irrespective of tree age. Yields varied according to density, with lower densities showing a higher yield efficiency per tree, but lower yield per ha. Thus, a higher yield is expected at higher densities, providing overcrowding can be managed. Overcrowding occurred in Vredendal, in the 10 x 5 m orchard, (year five), resulting in lower and reduced shoot growth compared to, lower density (10 x 8 m) orchard, with the same age. In paper 2, there was no significant difference in yield efficiency or nut quality between the cultivars in Vredendal. ’Choctaw’ produced bigger nuts in the second season, with significantly bigger trees in both seasons than ’Wichita’ and ’Navaho’, except for the volume of trees in the first season. Despite the difference in tree volume, no significant difference in light interception between cultivars was observed, indicating that tree shape, rather than volume, influenced light interception. Additionally, ’Navaho’ pecans demonstrated an earlier phenological development than ‘Choctaw’ and ‘Wichita’, with an earlier bud break and pollination period, which is critical to serve as cross-pollinator for ’Wichita’.

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