Abstract
Decreasing reliance on fertiliser Nitrogen (N) is key to enhancing the sustainability of pasture-based agricultural systems. This study assesses the effect of sward type on annual and seasonal herbage dry-matter (DM) production potential, sown species and unsown species contribution to herbage DM under an intensive dairy-calf to beef system. Three sward types were investigated in a farmlet experiment: Lolium perenne (LP; 205 kg N ha-1 a-1); L. perenne-Trifolium repens (LP-TR); multispecies sward consisting of L. perenne, Phleum pratense, T. repens, Trifolium pratense, Cichorium intybus and Plantago lanceolata (MSS). L. perenne-T. repens and MSS each received 92 kg N ha-1 a-1. Herbage samples were collected for DM production and botanical composition determination at each grazing. Further quadrat sampling was undertaken on three occasions per grazing season (early-, mid- and late-season), to enumerate the unsown species composition of swards and changes in bare ground. Over the course of the two-year study, LP, LP-TR and MSS produced annual herbage DM yields of 9950, 10,650 and 12,600 kg DM ha-1 a-1 respectively, despite reducing fertiliser N application to LP-TR and MSS by 55% compared to LP. The average proportional contribution of grass species to MSS’ herbage DM remained constant, the clover content of MSS increased, while the herb content decreased from 2020 to 2021. Seasonally, the proportional contribution of L. perenne and P. lanceolata to MSS’ herbage DM declined as the grazing season progressed, the contribution of T. repens and T. pratense increased and that of P. pratense and C. intybus remained similar. In LP-TR, T. repens’ proportional contribution to herbage DM increased from 2020 to 2021, while L. perenne’s proportional contribution declined. Seasonally, the proportional contribution of L. perenne to the herbage DM of LP-TR declined as the grazing season progressed, while the proportion of T. repens’ increased. The contribution of dead plant material to herbage DM increased across all swards in the second year but did not differ between sward types. Sward type did not affect the proportional contribution of unsown species by functional group to herbage DM. These results demonstrate that under a relatively-intensive beef grazing system, MSS receiving reduced N compared to LP monocultures, and the same N compared to LP-TR swards, produce more herbage DM, and do not have a greater weed (unsown species) burden. Overall, our findings demonstrate the potential of MSS to ‘produce more while using less’, a key requirement of sustainable grazing systems.
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