Phosphorus requirements for the establishment of two forage grasses in an acid soil

Abstract

The phosphorus and lime requirements for the establishment of the grasses Andropogon gayanus and Setaria sphacelata in a red-yellow, clayed latosol, were determined by means of two field experiments. Treatments comprised five rates of P₂O₅, as single superphosphate and three rates of dolomitic limestone. The P₂O₅ rates were: 0, 50, 100, 200 and 400kg/ha and the lime rates were 0, 0.5 and 1.0t/ha for A. gayanus and 0, 1.5 and 3.0t/ha for S. sphacelata. The duration of the experiments was two years, with two harvests per year. Lime had no significant effect on the dry matter yield of the two grasses. The critical soil P concentrations were 7.78 and 5.40 ppm for A. gayanus and 11.96 and 9.45 ppm for S. sphacelata, respectively in 1st harvest and year 1. The estimated P₂O₅ rates to increase soil P up to the values of the critical soil P concentrations were larger when the classes of available soil P were calculated using the data of the 1st harvest than those of year 1, particularly for soils of low P level.