Abstract Fertilisation, although it improves crop yield and enhances farmer income, can contribute to freshwater pollution. Thus, it is important to determine the recommended fertilisation rate that can ensure crop yield and farmer income, as well as not harm the environment. We calculated the yield and net income of tobacco and measured the nitrogen (N) and phosphorous (P) concentrations under different fertilisation rates in plot runoff and local stream water during 2017 and 2018. Tobacco yield increased with increasing fertilisation rates, but net income decreased at extremely high rates. The opposite pattern was observed for the fertiliser nutrient use efficiency (NUE). When fertilisation was applied, the N and P concentrations in the runoff exceeded the established national thresholds, and the concentrations and discharges of N and P in the runoff were positively correlated with the fertilisation rate. According to the ratio of arable land to the total watershed area, reduction characteristics of N and P in the watershed stream, and the established national thresholds, the recommended N and P2O5 annual application rates in the study area are 120 kg ha−1 for both fertilisers. The recommended rates are lower than what farmers currently apply. Therefore, reducing the synthetic fertiliser application rate should be implemented to achieve sustainable development in the study region.

中文翻译：

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基于当地河流水中的经济响应和养分浓度确定烟草的氮磷施肥率

摘要 施肥虽然可以提高作物产量并增加农民收入，但也会导致淡水污染。因此，确定可以确保作物产量和农民收入，同时又不损害环境的推荐施肥率非常重要。我们计算了 2017 年和 2018 年烟草的产量和净收入，并测量了不同施肥量下地块径流和当地河流水中的氮（N）和磷（P）浓度。烟草产量随着施肥量的增加而增加，但净收入下降以极高的速度。肥料养分利用效率（NUE）则观察到相反的模式。施肥时，径流中的 N 和 P 浓度超过既定的国家阈值，径流中N、P的浓度和排放量与施肥率呈正相关。根据耕地面积占流域总面积的比例、流域河流中氮、磷的减量特征以及国家设定的阈值，研究区推荐的氮、P2O5年施用量为120 kg ha−1肥料。建议的费率低于农民目前申请的费率。因此，应实施降低化肥施用量，以实现研究区的可持续发展。研究区推荐的 N 和 P2O5 年施用量为 120 kg ha-1，两种肥料均适用。建议的费率低于农民目前申请的费率。因此，应实施降低化肥施用量，以实现研究区的可持续发展。研究区推荐的 N 和 P2O5 年施用量为 120 kg ha-1，两种肥料均适用。建议的费率低于农民目前申请的费率。因此，应实施降低化肥施用量，以实现研究区的可持续发展。