Nitrogen (N) fertilizer is among the costliest inputs to maize ( L.) production, and the most challenging input to predict the optimum application for enhanced productivity while preventing loss to the environment. This study aimed to determine if late spring maize stalk sap nitrate-N concentrations measured during vegetative growth stages can be used to guide in-season N fertilizer input decisions. Maize stalk sap nitrate-N concentrations were measured at the seven to nine-leaf (V7-V9) developmental stage across eight sites (location-crop rotation-year) in Iowa. Each site received four to eight pre-plant N fertilizer rates. At each site, the stalk nitrate-N concentration consistently increased with the N fertilization rate. Relative grain yield was positively related to sap nitrate concentration. In addition, there was a positive relationship between sap nitrate concentration, tissue total N concentration, late spring soil nitrate test, and end-of-season maize stalk nitrate test. Overall, across all sites, the sap nitrate-N concentration that indicated N sufficiency (i.e., N supply sufficient to achieve the highest relative yield) spanned a relatively narrow range (715–893 mg N L sap) compared to the full observed range (22–1478 mg N L sap). Observations from this multi-site-year study suggest that stalk sap nitrate concentration has the potential to aid in-season N fertilizer application recommendations. Thus, it deserves further study considering other environmental and management factors that potentially affect the sap nitrate N concentrations. A stalk sap nitrate test along with rapid, reliable, and low-cost nitrate sensors can create unprecedented databases to optimize soil fertility and plant nutrition.

中文翻译：

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茎秆汁液硝酸盐测试作为玉米氮肥建议的潜在工具

氮 (N) 肥料是玉米 (L.) 生产中成本最高的投入之一，也是预测提高生产力同时防止环境损失的最佳施用量最具挑战性的投入。本研究旨在确定在营养生长阶段测量的晚春玉米秆汁液硝酸盐浓度是否可用于指导当季氮肥投入决策。在爱荷华州八个地点（位置-轮作年份）的七叶至九叶（V7-V9）发育阶段测量了玉米秆汁液硝酸盐-N浓度。每个地点接受四到八种种植前氮肥施用。在每个地点，茎秆硝酸盐氮浓度随着施氮量的增加而持续增加。相对谷物产量与汁液硝酸盐浓度呈正相关。此外，汁液硝酸盐浓度、组织全氮浓度、晚春土壤硝酸盐测试和季末玉米秆硝酸盐测试之间存在正相关关系。总体而言，在所有地点，与完整观察范围（22 –1478 毫克 NL 汁液）。这项多站点年度研究的观察结果表明，秸秆汁液硝酸盐浓度有可能有助于提出当季氮肥施用建议。因此，考虑到可能影响汁液硝酸盐氮浓度的其他环境和管理因素，值得进一步研究。茎秆汁液硝酸盐测试以及快速、可靠和低成本的硝酸盐传感器可以创建前所未有的数据库，以优化土壤肥力和植物营养。