The study aimed to evaluate the efficiency of nutrient use in three cactus forage (CF) cultivars (Opuntia stricta and Nopalea cochenillifera), 365 days after planting under different types of fertilizer in two research sites (Condado and Riachão) of the semi-arid region of Paraiba state, Brazil. The experimental design was a randomized block design with treatments in a factorial scheme (3×4), three cultivars of CF (Orelha de elefante Mexicana; Miúda; Bahiana), and four fertilizer treatment (Control; Manure; Manure with Nitrogen; Mineral fertilization) with four replications. The CF cultivars did not differ significantly in nutrient use. That means of physiological efficiency by CF cultivars were 1.62, and 2.36 kg of biomass per kg of nutrient applied in Condado and Riachão, respectively. The efficiency of nutrient recovery was 16% for the Condado, according the following order: K> P> Ca> N> C = Mg and 12% for Riachão: K> P> N> C = Ca = Mg. In the two research sites, the treatment with mineral fertilization significantly increased the efficiency use of N, P and K in comparison to the other treatments. The average for efficiency of nutrient utilization was 25% and 19% for Condado and Riachão, respectively, in the following order for Condado: K> P> N> Ca = Mg> C, and Riachão: K> P> N> C> Mg = Ca. In a CF production system aiming to obtain a yearly harvest cycle, it is necessary to replenish of K and P to maintain the nutritional balance between the soil and CF plant.
Sewage Sludge Treatment by Hydrothermal Carbonization: Feasibility Study for Sustainable Nutrient Recovery and Fuel Production