Effects of high rates of nitrogen fertiliser on dairy pastures and production

Abstract

High rates of nitrogen (N) fertiliser (217 and 324 kg N/ha/y) applied during a farrnlet study at No. 2 Dairy, DRC, Hamilton increased annual net herbage accumulation by 23% and 27% respectively. Increases in feed conservation and milk production reflected the extra pasture growth. On low stocked (3.2 cows/ha) farmlets where 219 and 330 kgN/ba/yr were used, clover contents declined to 12.5% and 3.4% respectively compared with 22.8% where no N was used. Decreased clover content was probably a result of competition from increased growth of ryegrass. At the high stocking rate (4.5 cows/ha), N application resulted in clover contents of 19.6% and 7.9% respectively, compared with 23.8% where no nitrogen was used. Pasture utilisation was better on these fannlets than under the lower stocking rate, suggesting the improved utilisation of additional feed, particularly during spring, was responsible for the higher clover content. Nitrogen fixation activity was lower in pastures which received N fertiliser due to both the decreased clover content and a reduction in activity per clover plant. Keywords: conservation, dairying, milk production, nitrogen fertiliser, pasture production, Trifolium repens