This study aimed to evaluate the effect of irrigation depths (IDs) with brackish water and levels of organic fertilizer (OF) on the morphological aspects, production, chemical composition and in vitro digestibility of cactus pear grown in a semiarid region. This experiment was conducted in an area already established for 2 years with cactus pear [Opuntia stricta (Haw.)] and started 18 months after the standardization cut. This was a 5 × 4 factorial design of five irrigation depths (0, 12.5, 25, 37.5 and 50% evapotranspiration—ETo) and four levels of organic fertilizer (0, 15, 30, and 45 megagram per hectare—Mg/ha), with four replications. The water used in the experiment was classified with high salinity and low sodium content (C3S1), and presented an electrical conductivity of 1.73 dS/m. There was no effect of the ID × OF interaction on the morphological and productive characteristics of cactus pear (p > 0.05); however, the ID × OF interaction promoted effects on ether extract, crude protein, neutral detergent insoluble protein, neutral detergent insoluble ash, total carbohydrates and non-fiber carbohydrates (p < 0.05). The ID and OF levels separately influenced the productive, morphological and nutritional characteristics of cactus pear. Under experimental conditions, we recommend the use of organic fertilizer at a level up to 45 Mg/ha, which is associated with the use of lower brackish water levels for the cultivation of cactus pear. This study’s findings provide new insights into reducing the use of potable water in crop irrigation for dryland regions and other regions.
