The yield response of annual ryegrass (Lolium multiflorum) to varying nitrogen fertilizer application strategies

Annual ryegrass (Lolium multiflorum LAM. cv. Midmar) pastures were established on three sites, representing the Avalon, Katspruit and Inanda soil forms, with cut-plot experimentation over a period of four years (1987 - 1990). Nitrogen fertilizer was top-dressed at 0, 200, 300 or 400 kg N ha−1 y−1 and at intervals of 4 or 6 weeks. The dry matter (DM) yield data indicates that there was little justification for applying more than 40 kg N ha−1 per application in autumn, and more than 50 kg N ha−1 per application during spring. In addition, pastures top- dressed 4-weekly, at the above rates, produced yields equal or superior to equivalent annual rates applied on a 6-weekly application interval. With the increase in environmental concern about nitrates leaching into ground waters, and the potential for excessive applied N to accumulate to potentially toxic levels in pastures, the adoption of large infrequent applications of N is questioned.