Araya Guzmán, Kimberly

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    Calibración del análisis de suelo de fósforo para la forrajera Brachiaria decumbens en un Ultisol, Puerto Rico
    (2024-03-05) Araya Guzmán, Kimberly; Sotomayor Ramírez, David; College of Agricultural Sciences; Martínez Rodríguez, Gustavo A.; Bair Gallegos, Daniel; Department of Agro-Environmental Sciences; Velázquez Augusto, Wesley
    Phosphorus (P) is one of the most limiting factors for forage production in the Tropics. Contrary to what should be done soil test P is not used as a guide to generate P fertilization recommendations in Puerto Rico. The response of the forage Brachiaria decumbens to five levels of P fertilization was evaluated: (P1) 0, (P2) 60, (P3) 120, (P4) 180, (P5) 240 kg P₂O₅/ha/year, in a Ultisol (Typic Haplustults) in southwest Puerto Rico with soil test P in the Low category. The increase in soil test P per applied fertilizer P ranged from 0.3 to 1.1 mg P/kg per 100 kg of P₂O₅ at the end of the experiment. B. decumbens responded to the application of P, but not at the expected magnitude. Dry matter (DM) yield increased 13% with P fertilization with a maximum yield of 18,613 kg DM/ha/year. Forage DM yield was fit to a modified Mitscherlich model, and a critical fertilizer P application level of 24 kg P₂O₅/ha/year was obtained, which is four times lower than the current P recommendation for pastures. P extraction estimates ranged from 27.5 and 52.2 kg P/ha/year and increased with fertilizer-P applied. P use efficiency and P balance demonstrated that the forage was highly efficient as it extracted at least 50% of the P applied in all treatments. The application of 60 kg P₂O₅/ha/year resulted in higher P use efficiency, improved partial productivity factor and a higher removal efficiency. A linear relationship was found between STP and P balance, suggesting its usefulness as a fertilizer-P management strategy. Discrete economic analysis demonstrates that fertilizer-P applications beyond 60 kg P₂O₅/ha/year have negative net and investment returns and should not be considered profitable P application levels.