ABSTRACT Nitrogen (N) fertilization is crucial for maximizing maize (Zea mays L.) yield, but optimizing the amount of N to apply for maize must also consider potential impact on the environment from nitrate-N pollution. The dark green color index (DGCI) technology determines the greenness of maize leaves to assess maize N status. Spectrum Technologies used this DGCI technology to develop a smartphone app called Greenindex+. The objective of this study was to determine if DGCI values made by the app (DGCIapp) agree with values determined by a digital camera (DGCIcam), and to identify the sources of potential discrepancies between the camera and the app for determining DGCI. Field experiments were conducted at six sites across the state of Arkansas during 2013 and 2014 with N rates ranging from 0 to 360 kg N ha−1. Dark green color index measurements were made at tasseling both in the field using the app under ambient lighting conditions and in the laboratory under fluorescent lighting using the camera and the app. There was a significant linear–plateau relationship (P ≤ 0.05, R2 = 0.60, 0.89) between DGCIcam and leaf N concentration. However, the relationship between DGCIapp and leaf N concentration was more variable (R2 = 0.33, 0.69) than between DGCIcam and leaf N concentration when measured in the laboratory. Under field conditions, DGCIapp was also more variable than DGCIcam measured in the laboratory. The variability between DGCIcam and DGCIapp is because DGCIcam uses the whole leaf for color analysis while DGCIapp uses only the center portion of the leaf for color analysis.

中文翻译：

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使用深绿色指数评估数码相机和智能手机应用程序在评估玉米氮状态时

摘要 氮 (N) 施肥对于最大限度地提高玉米 (Zea mays L.) 产量至关重要，但优化用于玉米的 N 量还必须考虑硝酸盐-N 污染对环境的潜在影响。深绿色指数 (DGCI) 技术通过确定玉米叶片的绿色度来评估玉米 N 状态。Spectrum Technologies 使用这种 DGCI 技术开发了一款名为 Greenindex+ 的智能手机应用程序。本研究的目的是确定应用程序 (DGCIapp) 确定的 DGCI 值是否与数码相机 (DGCIcam) 确定的值一致，并确定相机和应用程序之间用于确定 DGCI 的潜在差异的来源。2013 年和 2014 年期间，在阿肯色州的六个地点进行了田间试验，氮含量从 0 到 360 kg N ha-1。深绿色指数测量是在现场使用应用程序在环境照明条件下和在荧光灯照明下使用相机和应用程序在实验室中进行的。DGCIcam 与叶片 N 浓度之间存在显着的线性平台关系（P ≤ 0.05，R2 = 0.60，0.89）。然而，在实验室中测量时，DGCIapp 与叶片 N 浓度之间的关系比 DGCIcam 与叶片 N 浓度之间的变化更大（R2 = 0.33, 0.69）。在现场条件下，DGCIapp 也比实验室中测量的 DGCIcam 更具可变性。DGCIcam 和 DGCIapp 之间的差异是因为 DGCIcam 使用整个叶子进行颜色分析，而 DGCIapp 仅使用叶子的中心部分进行颜色分析。