Effects of weather variability on sheep and beef farming in northern Southland, New Zealand: A modelling analysis

Inter-annual weather variation has profound effects on pasture production and pastoral farm performance. However, the relationship between the variation in herbage and animal production and farm economic and environmental (nitrate leaching and greenhouse gas emission) outcomes are not clearly quantified, especially with varying farm management strategies applied under variable weather scenarios. We used a pasture model (APSIM-AgPasture), corroborated by measured pasture growth data, to generate pasture growth curves for a typical sheep and beef farm in northern Southland for the past 39 years, and grouped them into five weather scenarios. We fed these curves into a farm system model (Farmax) to examine the changes in farm performance with various management adaptations. We found that farm economic and environmental outcomes did not respond proportionally to pasture production; compared with the variation range in herbage production, the variation range in animal production was smaller, but the variation range in farm profitability was larger. Environmental efficiency (nitrate leaching and greenhouse gas emissions per unit of animal products) was high in wet years. Our results highlight the importance of considering the nonproportional changes among pasture production, animal production, profitability, and environmental outcomes of pastoral farming when selecting farm management strategies and tactics to adapt to weather variations, and indicate the necessity of incorporating these non-linear relationships in the development of farm management decision support tools.