Forage yield and quality on soil subjected to phosphorus rates in subtropical grassland of Brazil

Phosphorous application effects were evaluated on ryegrass dry matter (DM) accumulation, root development and plant tissue concentration of phosphorus, nitrogen and carbon aiming to determinate the nutritional status of the pasture, as well as to verify the possibility to establish a phosphorus dilution curve for this pasture. Also, the development of phosphorus and ryegrass cultivated with the residual effect of phosphorus fertilization was determined. The experiment was carried out in Pinhais County - Paraná State on a Cambisol with very low phosphorus levels. The experiment was of random blocks design and treatments consisted of five phosphorus rates of triple superphosphate (0, 45, 90, 180 and 360 kg P2O5 ha-1) applied to soil surface with four replications. Phosphorus fertilization promoted linear increments in the soil phosphorus availability and resulted, in the first year, in early pasture production and higher phosphorus content in the plant. Nitrogen and carbon contents were not affected. Phosphorous application increased ryegrass DM accumulation in all periods, ranging from 16 to 2826 kg DM ha-1 at flowering stage, for zero and 360 kg P2O5 ha-1, respectively. Root density was positively influenced by phosphorus supply, and the rate of 45 kg P2O5 ha-1 was effective for maximum root development. The residual effect of phosphorus fertilizer provided enhancement of yield and phosphorus plant concentration for both sorghum and ryegrass in the second year.