Plantain mixed pasture : seasonality of herbage accumulation and potential for mitigating nitrous oxide emissions from cow urine patches : a thesis presented in partial fulfilment of the requirements for the degree of Master in Horticulture Science at Massey University, Manawatū, New Zealand
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Date
2021
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Massey University
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There is growing evidence that plantain (Plantago lanceolata L.) is recognised by dairy farmers to improve summer feed productivity and quality and to mitigate nitrogen (N) pollution from grazed pastoral soils. However, there is still limited information on the proportion of plantain required when it is mixed with perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) pasture to optimise its yield stability and environmental benefits. The objectives of this thesis were to monitor seasonal changes in the contribution of plantain to perennial ryegrass/white clover pastures, and to evaluate the effect of incorporating plantain in the pasture diet of dairy cows on nitrous oxide (N₂O) emissions from urine patches during summer and autumn. The field experiment was conducted over two growing seasons (2019/2020 and 2020/2021). The research site consisted of 20 experimental plots: each plot was 800 m² (20 m x 40m). There were four treatments, with different proportions of plantain (0%, 30%, 50% and 70%) in ryegrass/white clover pastures. Each treatment was replicated five times. The proportion of plantain in the mixed pasture treatments reached a peak of 40% in the first growing season and of 50% in the second growing season during summer- autumn period. At the end of the first growing season following establishment of the treatments, the plantain proportion in the 50% and 70% plantain mixed pasture treatments were similar as around 50%. Plant density of plantain increased by 35% over the first growing season, but it decreased by 52–62% during the second growing season. Overall, the 30% and 50% plantain mixed pastures maintained more stable proportions of plantain than the 70% plantain mixed pasture treatment. Including 30% and 50% plantain in the summer/autumn grazed diet of dairy cows reduced the urinary-N concentration to 5.40 and 4.40g N L⁻¹, respectively, compared to 6.15g N L⁻¹ in urine from cows fed ryegrass and white clover. A lower N content in urine from cows grazing 50% plantain mixed pasture produced 39% less total N₂O emissions compared to ryegrass/white clover urine treatment, regardless of plantain treatments. Total N2O emissions and the emission factor (EF₃) for plantain mixed pastures were 16% and 27%, respectively, lower than for ryegrass/white clover pasture. The effect of plantain swards on decreased N₂O emissions was linked to changes in soil N-cycling and water-filled pore space values. Plantain proportions of 30% to 50% in mixed pastures were relatively stable over two growing seasons and reduced the urinary-N concentration resulting in the subsequently decreased in N₂O emissions from urine patches in summer/ autumn season.