The nitrogen-use efficiency (NUE) of a fertiliser has implications for pasture growth and the environment. This study aimed to compare application of urea as a foliar spray or in granular form, to kikuyu (Cenchrus clandestinus (Hochst. ex Chiov.) Morrone) and short-rotation ryegrass (Italian ryegrass, Lolium multiflorum Lam.) pastures in the subtropical dairy region of eastern Australia. The first experiment was a replicated grazing study on a site with a high plant-available soil N (75 mg nitrate-N/kg). The granular rate of urea was 46 kg N/ha.month equivalent, and the foliar spray rate was 40% of the granular rate. Pasture growth rate (51 DM/ha.day with foliar spray vs 45 kg DM/ha.day with granules) and pasture consumed (4942 vs 4382 kg DM/ha) were not significantly different between treatments. However, over the 8 months of the study, soil nitrate-N levels fell from 75 to 22 mg/kg on the foliar plots but only fell to 60 mg/kg on the granular plots. The second experiment was a replicated plot-cut experiment on a site with a low plant-available soil N (8.7 mg nitrate-N/kg). The NUE for kikuyu grass was similar for all treatments with a mean of 14.8 kg DM/kg N for the four foliar treatments (high and low, with and without wetting agent) and 17.4 kg DM/kg N for the granular treatment. The NUE for the ryegrass was also similar for all treatments, with a mean of 13.2 kg DM/kg N for the foliar treatments and 15.8 kg DM/ha for the granular treatment. A third experiment, evaluating absorption of foliar-sprayed urea over time, found that >80% of the urea applied to kikuyu was absorbed by 7 h; for ryegrass, the amount absorbed was only ~45% but increased to ~75% if wetting agent was included. We suggest that the lack of benefit in NUE achieved by applying urea as a foliar spray, which contrasts with results from studies in temperate dairy farm systems, is primarily associated with the substantially lower tiller density and hence the smaller canopy area for absorption of the foliar spray by the new regrowth shoots post-grazing.

肥料的氮利用效率（NUE）对牧场生长和环境具有影响。这项研究旨在比较叶面喷雾剂或颗粒剂形式的尿素在kikuyu（Cenchrus clandestinus（Hochst。ex Chiov。）Morrone）和短旋转黑麦草（Italian黑麦草，黑麦草）中的应用Lam。）在澳大利亚东部亚热带乳制品地区的牧场。第一个实验是在植物可用土壤氮含量较高（75毫克硝酸盐氮/千克）的场所进行的重复放牧研究。尿素的颗粒度为46 kg N / ha.month当量，而叶面喷洒率为颗粒度的40％。两种处理之间的牧草生长速度（叶面喷洒为51 DM / ha.vs颗粒为45 kg DM / ha.day）和牧草消耗量（4942 vs 4382 kg DM / ha）没有显着差异。然而，在研究的8个月中，叶面样地的土壤硝态氮水平从75毫克/千克下降至22毫克/千克，而颗粒样地仅下降至60毫克/千克。第二个实验是在土壤有效氮含量较低（8.7 mg硝酸盐-N / kg）的场地上进行的重复样板试验。在所有处理中，菊苣草的NUE均相似，平均值为14。四种叶面处理（高湿和低湿，有和没有湿润剂）的处理量为8 kg DM / kg N，颗粒处理的为17.4 kg DM / kgN。黑麦草的NUE在所有处理中也都相似，叶面处理的平均NUE为13.2 kg DM / kg，颗粒处理的平均NUE为15.8 kg DM / ha。第三个实验评估了随时间推移喷洒的叶面尿素的吸收量，发现施用到kikuyu的尿素中有> 80％在7小时内被吸收。对于黑麦草，吸收量仅为〜45％，但如果包括润湿剂，吸收量将增加至〜75％。我们建议通过将尿素用作叶面喷洒剂而在NUE方面缺乏益处，这与温带奶牛场系统的研究结果相反，