Effect of two phosphorus fertilizers on the yield of Andropogon gayanus in four soils with different physic and chemical properties. | Efecto de dos fuentes de fosforo sobre el rendimiento del pasto Andropogon gayanus en cuatro suelos con propiedades fisicas y quimicas variables.

English. With the purpose to contribute to define quantities and frecuency of application of phosphoric rock (PR), four field experiments were conducted: three experiments in Guarico State and one in Apure State. The soils of Guarico were classified like Typic Ustipsamments (La Ceba), Plinthaquic Paleustults (La Entrada); Plinthic Paleustults (Quintalito). The Apure's soil is an Ustic Quarsipsamments (Santa Rosa). The experimental design was a randomized block with eleven treatments and three replications. The PR treatments were 0-500-1000-1500 kg/ha; duplicates of these treatments were combined with triple superphosphate (TSP) and micronutrients zinc and copper. Andropogon gayanus was stablished in 1990 and this paper report two year evaluations (1991-1992). The results showed the differential responses in the four soils. In Typic Ustipsamments soil (La Ceba), there were not response to PR; this is a sandy soil with low aluminium and high calcium contents in the shallow horizont. The response in the Plinthic Paleustults (Quintalito) and Plinthaquic Paleustults (La Entrada) soils were high, the chemical properties on these soils were more restrictives (high Al, low calcium and phosphorus); the highest yield was clear at the calcium and phosphorus); the highest yield was obtained with 700 and 600 kg/ha respectively, and the residual effect was clear at the second year. In Santa Rosa soil the response was the lowest. In all cases the calcium and phosphorus contents of soil increses with treatments. The critical level of P in the soil was around 6 ppm by Olsen method, that suggest that this value is more appropiate for crops of low requirements of P. Is important to know the chemical and physical properties of soils before stabilishment of pastures and do the fertilizer recomendations, especially of PR.

Spanish; Castilian. Este trabajo se planifico con el objetivo principal de generar resultados que contribuyan a definir criterios que orienten las recomendaciones en cuanto a dosis y frecuencias de aplicacion de roca fosforica (RF). Se planificaron cuatro ensayos de campo, en bloques al azar con pasto Andropogon gayanus. Los tratamientos con RF fueron 0-500-1000 y 1500 kg/ha; duplicados de estos se combinaron con cobre, zinc, incluyendose un testigo absoluto, uno con nitrogeno, potasio y fosforo en forma de superfosfato triple: para un total de once tratamientos. Se seleccionaron tres sitios experimentales en la finca Las Patillas del Municipio Santa Maria de Ipire, Edo. Guarico y uno en el hato Santa Rosa en el Municipio Cunaviche, Edo. Apure. Los tres primeros se clasificaron como: Typic Ustipsamments (Potrero La Ceba); Plinthaquic Paleustults (Potrero La Entrada); Plinthic Paleustults (Potrero Quintalito); el de Apure Ustic Quarsipsamments (Santa Rosa). Los ensayos se establecieron durante 1990 y se resenan las evaluaciones de 1991 y 1992. Se puso de manifiesto un patron de respuesta diferente en los suelos con buena retencion de humedad y no fue tan limitante en cuanto a fertilidad, lo que favorecio el desarrollo del pasto. Hubo una alta respuesta a la fertilizacion fosfatada en los suelos de la Entrada y Quintalito los mayores beneficios se obtuvieron con 600 y 700 kg/ha de RF, respectivamente, obsevandose el efecto residual de esta al segundo ano. Los resultados reflejan la importancia de conocer las propiedades quimicas y fisicas de los suelos antes del establecimiento de pastizales y hacer las recomendaciones de fertilizantes especialmemnte de RF.