Applications of plant growth regulators such as paclobutrazol (PAC) to grain maize frequently caused depressions in grain yield. This negative impact probably originated from treatments at an early growth stage during plant ontogenesis when the determination of potential kernel number coincided with time of regulator application. However, stability of grain yield itself is of high relevance, and it is also the key determinant for harvest index (HI) and the use efficiencies of water (WUE) and nutrients (NUE). Therefore, in a container experiment, the effect of delayed PAC application at growth stage V8 was tested with the maize ( Zea mays L.) cultivars Galactus and Fabregas. Immediately after PAC treatment, differential N fertilization was introduced in order to meet the demand of the control plants (100% N), and with a supply of 75% N. With late PAC application (V8), grain yield depressions could not only successfully be avoided; moreover, in Galactus-75%N, a significant increase in grain yield was achieved combined with an extended duration of pollen shed by 28%. Straw yield decreased less strongly after late compared with early PAC application, leading to small, but significant increases in HI for the maize plants with 75% N supply. An increase in PAC dosage combined with later application will certainly lead to stronger decreases in straw yield, but it will also enhance the risk for grain yield depressions, and thus, an overall stronger improvement of HI is uncertain. For the time around silking, remarkable improvements of WUE_grain by 18% were achieved after delayed PAC application to Galactus-75%N. After PAC treatment, significant increases in nitrogen-harvest index (NHI) and thus N partitioning to grain were achieved for Fabregas and for Galactus-75%N. Although luxurious N consumption did not occur, late PAC application showed neither an effect on N-utilization efficiency (NUtE_grain) nor on N-uptake efficiency (NUpE). It can be concluded that it is a very complex task to achieve the right balance between PAC dosage, stability of grain yield and optimal N supply in order to avoid both, luxurious N consumption and N deficiency, and to achieve an improvement of NUtE_grain of maize plants.

中文翻译：

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通过将植物生长调节剂多效唑应用于氮供应减少的玉米植物，可以提高谷物产量、收获指数、水分利用效率和氮分配到谷物

多效唑 (PAC) 等植物生长调节剂在玉米上的应用经常导致谷物产量下降。这种负面影响可能源于植物个体发生过程中早期生长阶段的处理，当时潜在籽粒数的确定与调节剂应用的时间相吻合。然而，粮食产量的稳定性本身具有很高的相关性，它也是收获指数（HI）和水分（WUE）和养分利用效率（NUE）的关键决定因素。因此，在一个容器实验中，在 V8 生长阶段延迟施用 PAC 的效果用玉米（Zea maysL.) 品种 Galactus 和 Fabregas。在 PAC 处理后，立即引入差异化施氮以满足对照植物的需求（100% N），并提供 75% N 的供应。通过后期 PAC 施用（V8），谷物产量下降不仅可以成功避免；此外，在 Galactus-75%N 中，谷物产量显着增加，花粉脱落持续时间延长了 28%。与早期施用 PAC 相比，后期秸秆产量下降幅度较小，导致氮供应量为 75% 的玉米植株的 HI 略有但显着增加。PAC用量的增加和后期施用肯定会导致秸秆产量下降幅度更大，但也会增加粮食减产的风险，因此，HI总体上是否有更大的改善是不确定的。在延迟将 PAC 应用于 Galactus-75%N 后，_{颗粒增加了 18%。}经过 PAC 处理后，Fabregas 和 Galactus-75%N 的氮收获指数 (NHI) 显着增加，因此 N 分配到谷物中。_{尽管没有发生过度的 N 消耗，但后期 PAC 应用对 N-利用效率（NUtE谷物}）和 N-吸收效率（NUpE）都没有影响。可以得出结论，要在 PAC 用量、谷物产量稳定性和最佳 N 供应之间取得适当的平衡，以避免过度的 N 消耗和 N 缺乏，并实现 NUtE 谷物的改善，这是一项非常复杂_的任务玉米植物。