Ecophysiology of Soursop Seedlings Irrigated with Fish Farming Effluent under NPK Doses

Soursop (Annona muricata L.) is a tropical fruit grown in the semi-arid region of Brazil, where problems of quantitative and qualitative scarcity of water for irrigation are frequent. Using alternative water sources, such as fish farming effluents, can increase water availability; however, it presents risks due to its high salinity levels. We aimed to evaluate the effect of irrigation with saline fish farming effluent and NPK doses on soursop seedlings’ ecophysiology. We conducted a greenhouse experiment using a randomized complete block design with a 2 × 5 factorial scheme. The factors consisted of two irrigation water sources (local supply water with 0.5 dS m−1 and fish farming effluent with 3.5 dS m−1) and five doses of NPK (25%, 50%, 75%, 100%, and 125% of the fertilizer recommendation of 100:300:150 mg dm−3 of N:P2O5:K2O for soil). The soursop seedlings showed the best growth results for plant height, stem diameter, and shoot dry mass when irrigated with low-salinity water at 95% of the recommended NPK dose. However, under saline stress, the soursop seedlings showed optimal growth when fertilized with 69% of NPK dose. We recommend the following NPK fertilization for soursop seedlings: 95:285:143 mg dm−3 of N:P2O5:K2O for those irrigated with low-salinity water and 69:207:104 mg dm−3 for those irrigated with fish farm effluent. Irrigating with fish farm effluent can be a practical option for soursop seedlings as it can help save fertilizers and promote environmental sustainability.