Simulated seasonal responses of grazed dairy pastures to nitrogen fertilizer in SE Australia: N loss and recovery
Simulated seasonal responses of grazed dairy pastures to nitrogen fertilizer in SE Australia: N loss and recovery
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DOI：
10.1016/j.agsy.2020.102847
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发表时间：
2020-06-01
影响因子：
6.6
通讯作者：
Eckard, R. J.
中科院分区：
文献类型：
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作者：
Christie, K. M.;Smith, A. P.;Eckard, R. J.
来自农场水平研究的证据表明，澳大利亚奶牛场的氮肥（N）利用率有提高的潜力。增加氮肥施用量以推动牧草干物质生产超过农艺或经济最佳值有可能导致有害的环境后果。我们的研究，使用生物物理的整个农场系统模型DairyMod，模拟了一系列的氮肥施用率对总氮损失的五个奶牛场通过澳大利亚东南部，使用18年的历史气候。估算了植物生物量中的氮素积累量和根区及根区以下土壤中的氮素积累量。氮素以挥发、淋溶、径流和反硝化的形式流失到环境中。相对于最大牧草产量（Ymax），达到90%相对产量（Y 90）所需的氮肥投入减少量在所有地点和季节均> 50%。当肥料从Ymax减少到Y 90时，总氮损失的相关减少在34%和74%之间变化，取决于场地和季节。氮回收率（生物量中回收的氮相对于施氮量的比例）在大多数地点和季节都超过100%，但施氮量较低（< 30 kg N ha（-1）月（-1））。对氮的需求很高，在春季由于高牧草生长，这是支持通过氮矿化和遗产氮积累在冬季。四个温带站点的硝态氮淋失风险在冬季最高，亚热带站点的硝态氮淋失风险在秋季最高。这项研究表明，制定现场和季节性氮肥最佳管理实践指南，既经济又环保的好处。在考虑是否增加肥料时，需要权衡额外牧草产量的价值与环境氮损失和额外氮肥的成本。季节性土壤和气候条件之间的关系和氮素损失和恢复也进行了研究，为一个被覆盖的网站。由于这项研究没有考虑与N损失相关的外部性，建议需要考虑和修改的位置特异性和季节性气候条件的背景下。
Evidence from farm level studies indicates that there is potential to improve nitrogen (N) fertilizer efficiency of Australian dairy farms. Increasing N fertilizer application rates to drive pasture dry matter production beyond an agronomic or economical optimum has the potential to result in detrimental environmental outcomes. Our study, using the biophysical whole-farm systems model DairyMod, modelled a range of N fertilizer rates on total N loss for five dairy sites through south-eastern Australia, using 18 years of historical climate. Nitrogen accumulation in plant biomass and soil N accumulation within and below the rootzone were estimated. Total N loss, in the form of volatilization, leaching, runoff and denitrification lost to the environment were also estimated. The reduction in N fertilizer inputs required to achieve 90% of relative yield (Y90), relative to maximum pasture production (Ymax), was > 50% across all sites and seasons. The associated reduction in total N loss when fertilizer was reduced from Ymax to Y90, varied between 34% and 74%, depending on site and season. Nitrogen recovery (proportion of N recovered in biomass relative to N fertilizer applied) exceeded 100% with lower N fertilizer rates (< 30 kg N ha(-1) month(-1)) for most sites and seasons. Demand for N was high during spring due to high pasture growth and this was supported via N mineralization and legacy N build-up in winter. Nitrate leaching risk was highest in winter for the four temperate sites and autumn at the subtropical site. This study demonstrated the benefits of developing site and seasonal-specific N fertilizer best management practice guidelines that are both economical and environmentally beneficial. When considering whether to add more fertilizer, the value of additional pasture production needs to be weighed up against environmental N losses and the cost of additional N fertilizer to achieve this. The relationship between seasonal soil and climatic conditions and N loss and recovery were also examined for one rainfed site. As this study does not consider the externalities associated with N loss, recommendations need to be considered and amended in the context of location specificity and seasonal climatic conditions.