Growth Rate and Water-Use Efficiency of Cactus PearsOpuntia ficus-indicaandO. robusta

There is a lack of knowledge on water-use efficiency (WUE) of cactus pear under field conditions for a full growing season. Therefore, the growth rate and WUE (relationship between evapotranspiration and growth) was quantified for one to four-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. Although not significant (p > 0.05), evapotranspiration of O. ficus-indica was higher than that of O. robusta over the four growing seasons. The water content in the cladodes ranged between 88.02 and 88.21% for O. ficus-indica and for O. robusta between 87.23 and 87.52% (p < 0.05). The mean cladode fresh mass for the four growing seasons were 1,299 g cladode−1 for O. ficus-indica and 1,091 g cladode−1 for O. robusta (p < 0.05). The four-year-old plants produced in total as much as 9,665 and 8,378 kg dry mass (DM) ha−1 for O. ficus-indica and O. robusta, respectively. The relative growth rate and WUE of O. ficus-indica plants were higher (p < 0.05) than that of O. robusta for all four growing seasons. After four years of establishment, O. ficus-indica produced 7.87 kg DM ha−1 for each mm of water used compared to a WUE of 7.66 kg DM ha−1 mm−1 obtained for O. robusta(p < 0.05). Due to the highly favorable WUE of Opuntia species, it can be cultivated very successfully for forage production under arid and semi-arid climates and therefore utilize the more arid areas to their full potential.