The potential of diverse pastures to red

The effect of dairy cows grazing diverse pastures on whole farm productivity and urinary nitrogen (UN) excretion was evaluated using the DairyNZ Whole Farm Model. Two farms running typical systems; Scott Farm in the Waikato region (stocking rate = 3.2 cows/ha) and Lincoln University Dairy Farm in the Canterbury region (stocking rate = 3.9) with Holstein-Friesian x Jersey crossbred cows, were modelled over the 2011-2012 season. The effect of diverse pastures was assessed using three scenarios; the standard pasture (the traditional New Zealand perennial ryegrass-white clover pasture mix; control), and this pasture combined with diverse pasture sown on 20 or 50% (‘20% diverse’ or ‘50% diverse’) of the farm area, with the remainder sown in standard pasture. The diverse pasture comprised a mixture of standard pasture, chicory, plantain, prairie grass and either lucerne in the Waikato or red clover in Canterbury. Supplements were fed during deficits. The model outputs were farm-grown dry matter (DM) production, imported feed, milksolids production and UN. In both regions, the ‘20% diverse’ resulted in 1-2% lower DM production, but the higher feed energy content reduced intakes resulting in 4-19% less imported feed, compared with the control. In the Waikato, the 6% lower DM production for the ‘50% diverse’ compared with the control was only partly compensated for by increased energy content and an increase of 67% imported feed was predicted. In Canterbury, there was indication of diverse pasture benefiting from irrigation with 2% greater DM production and 46% less imported feed predicted for the ‘50% diverse’, compared with control. Milksolids production was similar across treatments, except for an increase of 3% predicted for the ‘50% diverse’, relative to the control in Canterbury. In both regions, feeding diverse pasture resulted in 3-7% less UN excretion. This study suggests that incorporating diverse pastures in New Zealand dairy systems can reduce UN excretion by dairy cows and mitigate the risk of nitrate leaching.