ROOT DISTRIBUTION OF CACTUS PEARS OPUNTIA FICUS-INDICA AND O. ROBUSTA - H. A. Snyman

Department of Animal, Wildlife & Grassland Sciences, University of the Free State, Bloemfontein 9300, South Africa

The cultivation of cactus pear has been gaining popularity in South Africa over the last 10 years as an alternative crop (fodder and fruit) for arid and semi-arid areas.  There is a lack of knowledge on the root dynamics of cactus pear for sustainable production in these drier areas.  This study was conducted during the 2003/2004 growing season on two-year-old Opuntia ficus-indica (L.) Miller (cultivar Morado – green cladode) and O. robusta Wendl. (cultivar Monterey – blue cladode) plants in the field and was aimed at quantifying root distribution in terms of distance and depth from the stem.  Root growth was expressed in terms of both mass and length.  In both species most roots were concentrated in the first 150 mm soil layer.  After only two growing seasons the roots spread as far as 2.5 m from the stem for both species.  The total root mass (dry) calculated per plant up to 1 200 mm  depth, were 239 and 316 g or kg ha-1 for O. ficus-indica and O. robusta respectively.  The thickest roots developed directly from the planted cladode and were 9.1 mm in circumference for O. ficus-indica and 6.3 mm for O. robusta.  Opuntia robusta showed a finer root system than that of O. ficus-indica.  After two growing seasons 3 407 and 2 702 kg ha-1 above-ground dry mass was produced by O. ficus-indica and O. robusta respectively.  The roots comprised only 11% for O. robusta and 7% for O. ficus-indica of the total biomass.  Opuntia is a drought tolerant crop and even the smallest amount of water is absorbed efficiently through the shallow and horizontally distributed root system.  In order to obtain a clearer picture of the complete dynamics of the root system of the cactus pear, more intensive research on the root distribution in plantations of different ages and different soil types will have to be carried out.