Aims The improvement of nitrogen use efficiency (NUE) of crops allows crop nitrogen (N) demands to be met while reducing N supply, and so reducing excess N which has potential negative environmental implications. NUE is often determined destructively at the end of crop growth-cycles without considering temporal variability. Here we present a methodological study which optimises the determination of NUE throughout the sugarcane growth-cycle using minimally destructive methods, and suggest the use of these methods for non-destructive NUE determination over the growth-cycle of other giant C4 crops. Methods and results The determination of the NUE relied on the optimisation of three methods: the estimation of aboveground biomass, N content and N derived from fertiliser (NdfF). First, the ability of different allometric relationships to estimate sugarcane biomass was investigated by selecting a relationship based on height and diameter to estimate aboveground biomass along the crop growth-cycle. Secondly, we assessed the minimum number of harvested sugarcane required to construct a dilution curve to predict N content from biomass and found that a sampling of 5 sugarcane at 3 dates was sufficient to represent aboveground N content over the growth-cycle. Finally, the ability of 15 N content of individual leaves to represent the NdfF in 15 N-fertilised cane was tested. The first and second leaf below the top visible dewlap were the most representative. Based on a variance analysis, we assessed the level of influence of each method on the NUE calculation. Crop age accounted for 54% of the variance of NUE, the choice of 15 N leaf 13%, with the choice of model to estimate biomass and the number of plants harvested for the N dilution curve, each accounting for less than 2% over the four sampling dates. Conclusions This study highlighted the importance of evaluating NUE not only at the point of harvest. We propose, therefore, a set of methods to study NUE throughout the sugarcane growth-cycle by using minimally destructive sampling.

中文翻译：

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优化非破坏性采样方法以研究巨型 C4 作物整个生长周期的氮利用效率

目标 提高作物的氮利用效率 (NUE) 可以满足作物对氮 (N) 的需求，同时减少 N 供应，从而减少对环境具有潜在负面影响的过量 N。NUE 通常是在作物生长周期结束时以破坏性方式确定的，而不考虑时间变异性。在这里，我们提出了一种方法学研究，该研究使用破坏性最小的方法优化了整个甘蔗生长周期中 NUE 的测定，并建议使用这些方法在其他巨型 C4 作物的生长周期中进行非破坏性 NUE 测定。方法和结果 NUE 的确定依赖于三种方法的优化：地上生物量、N 含量和来自肥料的 N (NdfF) 的估计。第一的，通过选择基于高度和直径的关系来估算作物生长周期的地上生物量，研究了不同异速生长关系估算甘蔗生物量的能力。其次，我们评估了构建稀释曲线以预测来自生物量的 N 含量所需的最少收获甘蔗数量，并发现在 3 个日期取样 5 个甘蔗足以代表整个生长周期中的地上 N 含量。最后，测试了单个叶子的 15 N 含量代表 15 N 施肥甘蔗中 NdfF 的能力。顶部可见赘肉下方的第一片和第二片叶子最具代表性。基于方差分析，我们评估了每种方法对 NUE 计算的影响程度。作物年龄占 NUE 方差的 54%，选择 15 N 叶 13%，选择模型来估计生物量和 N 稀释曲线收获的植物数量，在四个采样日期中每个都占不到 2%。结论 本研究强调了不仅在收获时评估 NUE 的重要性。因此，我们提出了一套方法，通过使用破坏性最小的采样来研究整个甘蔗生长周期的 NUE。