The role and value of diverse sward mixtures in dairy farm systems of New Zealand: An exploratory assessment

New Zealand dairy farm systems mostly rely on ryegrass-white clover pastures. The inclusion of diverse sward mixtures within these systems offers a novel strategy to improve economic and environmental outcomes. However, the degree to which these mixtures offer advantages over traditional pastures is unknown. This analysis seeks to explore the role and value of diverse mixtures to New Zealand dairy farms, through integrating the results of recent experimental research involving diverse sward mixtures with an existing whole-farm model. An exploratory assessment is required to determine further investment in these species, guide further data collection and experimental design, and understand traits of high value to farming systems. Model output suggests that the economic incentives associated with the use of diverse swards are too weak on their own to motivate wide-scale adoption under standard conditions. This finding is highly robust to changes in the milk price. However, given societal concern pertaining to water-quality deterioration, reductions in the levels of nitrogen lost from dairy farms are found to add substantially to the value proposition offered by alternative sward species. Reductions in nitrogen leaching of about 40% were predicted here when all the sward area on the farm is sown to diverse sward mixtures, compared with standard mixtures. This is mainly derived from a reduction in the concentration of nitrogen present in urine, and to a much lesser extent by a reduction in the total amount of urinary nitrogen excreted by cows. Overall, diverse swards appear to be a cost-effective way to reduce nitrogen leaching, which is relevant for a dairy sector facing regulatory constraints. Nevertheless, the need to understand and improve the persistence of diverse swards is important to reduce the cost of pasture establishment. (C) 2016 Elsevier Ltd. All rights reserved.