A urine patch model for evaluating management strategies for reducing nitrogen leaching from pasture-based dairy farms

Abstract Animal urine and urine patch characteristics are important drivers of nitrogen leaching in pasture-based dairy systems and their manipulation offers opportunities to mitigate these losses. We developed a model, based on previous work, to investigate the effect of applying tactical management strategies to reduce nitrogen leaching from urination events during different times of the year. Our model predicted that reducing pasture height or decreasing the volume per urination event to increase the spread of urine in the critical summer and autumn months (January to May) had minimal effect on nitrogen leaching at paddock scale. In contrast, diluting the nitrogen concentration of urine by decreasing dietary nitrogen intake by 30% or increasing total daily urination volume by 40% (while keeping daily nitrogen excreted constant) during these critical months reduced nitrogen leaching by 28% and 13%, respectively. When these dilution strategies were applied for the whole milking season (August to May) reductions of 40% and 22% were achieved. This demonstrates that management strategies can be applied tactically during key times of the year and still achieve considerable nitrogen leaching reductions. This is important for dairy producers who can add substantial reductions to nitrogen leaching from their farm systems, while reducing the management effort and costs by focussing on one key urine characteristic, nitrogen concentration, and only during a limited time of the farm season.