WATER-USE EFFICIENCY 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

Commercial cultivation of cactus pear in South Africa is a recent under¬taking.  Unfortunately there is a lack of knowledge on water-use efficiency (WUE) of cactus pear at community level, under field conditions, over a whole growing season.  From an agronomical point of view, this kind of information is of great significance, both in theory and in practice.  Therefore, the WUE (cladode dry-mass production per unit of evapotranspiration) was quantified for one, two and three-year-old Opuntia ficus-indica (L.) Miller (cultivar Morado, green cladode) and O. robusta Wendl. (cultivar Monterey, blue cladode) plants, in a semi-arid climate.  Evapotranspiration of O. ficus-indica was higher (P>0.05) over all three seasons than that of O. robusta.  The water content in the cladodes ranged between 88.02% and 88.19% for O. ficus-indica and between 87.23% and 87.51% for O. robusta.  Both Opuntia species showed an enormous increase in biomass production and WUE from the one to three-year-old plants.  The mean cladode fresh mass for the three growing seasons were 1 260 g cladode-1 for O. ficus-indica and 1 049 g cladode-1 for O. robusta. The three-year-old plants produced as much as 4 460 kg and 3 710 kg dry mass ha-1 for O. ficus-indica and O. robusta respectively.  The biomass production and WUE of the one, two and three-year-old O. ficus-indica plants were significantly (p< 0.01) higher than that of O. robusta.  After three years Opuntia ficus-indica produced as much as 11.99 kg dry matter (DM) ha-1 for each mm of water used, compared to 9.49 kg DM ha-1mm-1 obtained for O. robusta.  The above-mentioned characteristics of the cactus pear make it more appropriate for arid and semi-arid crop production.  It can therefore provide feed for livestock when this commodity is urgently required in drier areas.