Evaluation of calcium ammonium nitrate and urea-based fertilisers applied to grassland in Ireland

摘要

This study investigated the influence of N source and rate, and timing of N application on dry matter yield (DMY), N responses, N uptake and N use efficiency (NUE) in a grass crop. The experiment used three fertiliser treatments: CAN, urea and nBTPT-coated urea (nBTPT-U), three N rates (0 - control, 25, 50 and 75 kg ha~(-1)), and 18 fertiliser application timings. The agronomic performance of urea was lower than CAN in early spring. This included relatively lower N responses, lower relative DMY (90%)and N uptake (85%) which translated in lower NUE (0.45 vs. 0.70 kg kg~(-1)). For N applications later in the spring both urea and nBTPT-U showed relative DMY and NUE which were within ±5% compared with CAN (100%). nBTPT enhanced the overall performanceof urea which was shown with increased temperature towards the summer or increased N rates. In the summer, the efficiency of urea was lower than CAN or nBTPT-U in all measured parameters. The variability of urea and nBTPT-U as N-sources for grass was comparable to CAN but DMY with urea was ￡95% that of CAN (100%) at 8 out of the 19 application timings. Increasing the application rate of urea-N to offset its relatively lower efficiency may not be recommended since DMY of urea-N relative to CAN decreased with increased N fertilisation levels. However, with the use of nBTPT this may be possible, but fertiliser choice needs to be based on the relative costs per unit N.