The effects of strategic nitrogen fertiliser application during the cool season on perennial ryegrass-white clover pastures in the Western Cape Province 4. Selected nutritive characteristics and mineral content
The influence of a single application of fertiliser N (0, 50, 100 and 150 kg N ha-1) applied in either autumn, early winter, late winter, early spring or late spring on selected nutritive and mineral parameters of a perennial ryegrass-white clover pasture was investigated over a three-year period. Responses were measured over one regrowth cycle five weeks after the application of N treatments. A sample of the plant material harvested was separated into grass and clover fractions. Dry matter (DM), crude protein (CP), in vitro organic matter digestibility (IVOMD), phosphorus (P) and calcium (Ca) content were determined for each sample. Winter applications of fertiliser N, in combination with the higher N rates, resulted in higher ryegrass CP contents. Clover CP content was decreased (P=0.05) with spring (early and late) applications, but fertiliser N rate did not appear to affect clover CP content. The highest IVOMD values for both ryegrass and clover were recorded in winter. Increased fertiliser N rate resulted in lower DM contents with the lowest DM produced during winter, while the highest DM contents were produced where no fertiliser N was applied in spring. P content was significantly influenced by season of application and fertiliser N rate in ryegrass and only by season of application in clover. The highest mineral concentrations were found in winter. The rate and season of fertiliser N application as used in this study did not negatively affect pasture mineral content and quality, but care must be taken to protect the grazing animal from the potential negative effects of high forage N contents on animal health.