Yield, plant numbers, and tiller numbers were measured on broadcast swards of a mixture of ‘Grasslands Manawa’ and ‘Grasslands Ruanui’ ryegrass and on simulated swards of monocultures and a mixture of the ryegrasses grown at contrasting levels of nitrogen and phosphorus and under two cutting frequencies. Greatest yield responses were to applied nitrogen, but this response varied with season, and interacted with the other treatment effects. Overall, small yield increases were obtained by applying phosphorus, and greater yield was obtained with infrequent cutting. Response to phosphorus was relatively greater under frequent cutting. During flowering, response to nitrogen was relatively greater where cutting was infrequent. Initially Manawa grew more than Ruanui, giving Manawa a competitive advantage in all treatments. Manawa dominance was increased by applied nitrogen, and in broadcast swards this dominance was greater with infrequent cutting. In simulated swards, low seeding density and sub-optima...