Response of native pasture to nitrogen and phosphate fertilizer at Katherine, N.T

Abstract

A factorial combination of three levels of nitrogen and three levels of phosphate fertilizer was imposed on native pasture at Katherine over three years from 1956 to 1959. The pasture was composed largely of Sorghum plumosum and Themeda australis. A marked interaction between fertilizers in total dry matter yield was recorded; significant yield increases were obtained only in the presence of both nutrients. Sorghum showed independent responses to nitrogen and phosphate. Themeda was favoured only by a balanced nutrient supply, and with nitrogen in the absence of applied phosphate or vice versa its yield was reduced. The mean nitrogen content of the pasture increased substantially only when nitrogen was applied without phosphate. Response in total nitrogen yield to applied nitrogen and phosphate was independent ; where both nutrients were applied the response was mainly in dg matter yield with little change in nitrogen content, and when only one nutrient was applied the reverse held. Mean phosphorus content increased with increasing level of applied phosphate and decreasing level of applied nitrogen ; the changes were largely independent between fertilizers. Total phosphorus yield increased with increasing level of applied phosphate but was little affected by the level of applied nitrogen. Recovery of nitrogen fertilizer was extremely low, ranging from 5-6 per cent in the absence of applied phosphate to 8-9 per cent at the highest level of phosphate. The practical and ecological implications of the results are discussed.