Agricultural Reuse of Aquaculture Effluents: Morphometric and Productive Responses of Forage Cactus and Implications for Sustainability in the Brazilian Semiarid Region

The growing scarcity of freshwater necessitates sustainable alternatives, such as the use of aquaculture effluent to irrigate drought-resistant crops like Opuntia cochenillifera (Nopalea cochenillifera). This study aimed to evaluate the morphometric and productive variables of forage cactus under fertigation with aquaculture effluent in the Brazilian semiarid region. The experiment was conducted at the Universidade Federal Rural do Semi-Árido, Mossoró, Rio Grande do Norte, Brazil, using a randomized complete block design with five replications in a split-plot-in-time arrangement. The main plots comprised five aquaculture effluent proportions (0, 25, 50, 75, and 100%) in the irrigation mixtures, while the subplots corresponded to two successive cultivation cycles (A1 and A2). After 26 months of forage cactus cultivation, 11 morphometric and productive variables were evaluated and subjected to descriptive and multivariate statistical analyses. The use of aquaculture effluent replaced up to 41.3% of the water supply in the second cycle (A2), with no significant main effects on morphometric and productive attributes. However, the interaction between proportions and cycles was significant for the volume of fresh phytomass and the fresh mass per plant. In cycle A2, the treatment with 25% effluent resulted in a higher fresh mass per plant (3,996 ± 457 g plant− 1) compared to the treatment with 50% effluent (1,979 ± 457 g plant− 1). The first two principal components accounted for approximately 78% of the total variability, revealing strong associations between cladode development and biomass production. No proportion of effluent caused a statistically detectable reduction in yield compared to the control. The utilization of aquaculture effluents links water circularity to forage production in the semi-arid region. Interactions between the effluent and the cycle influenced biomass, although the main effects were not significant. Principal component analysis explained approximately 78% of the variability, relating cladode characteristics to biomass.