The effects of three shade densities, NPK fertilizers and fertilizer-pest/disease relationship on Amazon cocoa (Theobroma cacao L.) over a 20-year period are reported. Yields equivalent to the mean yield from the unfertilized plots were achieved in about 3, 4 and 6 years in fertilized plots under the no shade (S o ), medium shade (S,) and heavy shade (S 2 ) treatments, respectively. There were three growth phases, each characterized by a different yield trend. No appreciable changes in the exchangeable Ca and Mg were observed during the experiments, but K dropped to 68% of its initial value while the available P of the unfertilized and the S o plots fell by 38%. Fertilizer recommendations for P and K should take account of overhead shade. The effect of N application was often negative. No direct relationship was observed between fertilizer treatment and the incidence of pest/blackpod/swollen shoot virus (SSV) disease of cocoa. SSV infection was greatest under S o . Cocoa farms in Ghana cannot maintain high yields (above 1000 kg dry cocoa ha"') beyond 15 years of intensive cropping. Y. Ahenkorah, B. J. Halm, M. R. Appiah, G. S. Akrofi y J. E. K. Yirenkyi: Resultados de veinte anos de una prueba de sombra y fertilizante en el cacao amazonico (Theobroma cacaoj en Ghana. RESUMENSe informa sobre los efectos de tres densidades de sombra, fertilizantes NPK y la relacion fertilizante-plaga/enfermedad en el cacao amazonico (Theobroma cacao L.) durante un pen'odo de 20 anos. Rendimientos equivalentes al rendimiento medio de parcelas no fertilizadas fueron logradas en unos 3, 4 y 6 anos en las parcelas fertilizadas bajo los tratamientos sin sombra (S o ), sombra mediana (SJ, y sombra intensa (S 2 ) respectivamente. Se dieron tres fases de crecimiento, cada una caracterizada por una tendencia de rendimiento diferente. No se observaron cambios apreciables en el Ca y Mg intercambiable durante los experimentos, pero el K bajo al 68% de su valor inicial cuando el P disponible de las parcelas no fertilizadas y S o bajo un 38%. Las recomendaciones de fertilizante para P y K debenan contemplar la sombra que viene de arriba. El efecto de la aplicacion de N fue con frecuencia negativo. No se observo relacion directa entre el tratamiento de fertilizante y la incidencia de plaga/podredumbre negra de las bellotas/virus de la enfermedad de retono hinchado (SSV) del cacao. La infeccion SSV fue maxima bajo S o . Las plantaciones de cacao en Ghana no pueden mantener altos rendimientos (mayores de 1000 kg cacao seco hectarea" 1 ) mas alia de los 15 anos de cultivo intensive INTRODUCTION
SUMMARYThe effects of three shade densities, NPK fertilizers and fertilizer-pest/disease relationship on Amazon cocoa (Theobroma cacao L.) over a 20-year period are reported. Yields equivalent to the mean yield from the unfertilized plots were achieved in about 3, 4 and 6 years in fertilized plots under the no shade (S0), medium shade (S1) and heavy shade (S2) treatments, respectively. There were three growth phases, each characterized by a different yield trend. No appreciable changes in the exchangeable Ca and Mg were observed during the experiments, but K dropped to 68% of its initial value while the available P of the unfertilized and the S0 plots fell by 38%. Fertilizer recommendations for P and K should take account of overhead shade. The effect of N application was often negative. No direct relationship was observed between fertilizer treatment and the incidence of pest/blackpod/swollen shoot virus (SSV) disease of cocoa. SSV infection was greatest under S0. Cocoa farms in Ghana cannot maintain high yields (above 1000 kg dry cocoa ha−1) beyond 15 years of intensive cropping.
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