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 (DGCI_app) agree with values determined by a digital camera (DGCI_cam), 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 DGCI_cam and leaf N concentration. However, the relationship between DGCI_app and leaf N concentration was more variable (R² = 0.33, 0.69) than between DGCI_cam and leaf N concentration when measured in the laboratory. Under field conditions, DGCI_app was also more variable than DGCI_cam measured in the laboratory. The variability between DGCI_cam and DGCI_app is because DGCI_cam uses the whole leaf for color analysis while DGCI_app uses only the center portion of the leaf for color analysis.

氮（N）的施肥对于最大化玉米（Zea mays L.）的产量至关重要，但是优化氮的施用量也必须考虑硝态氮污染对环境的潜在影响。深绿色指数（DGCI）技术确定了玉米叶片的绿色程度，以评估玉米的氮状况。Spectrum Technologies使用此DGCI技术开发了一个名为Greenindex +的智能手机应用程序。这项研究的目的是确定应用程序（DGCI _app）生成的DGCI值是否与数码相机（DGCI _cam）确定的值一致），并确定相机与确定DGCI的应用之间潜在差异的来源。在2013年和2014年期间，在阿肯色州的六个地点进行了田间试验，氮的施用量为0至360 kg N ha ^-1。在环境光照条件下使用该应用程序在野外和实验室中在荧光灯照明下使用照相机和该应用程序在去雄时进行暗绿色指数测量。有一个显著线性高原关系（P ≤0.05，R ²  DGCI之间= 0.60，0.89）_凸轮和叶N浓度。但是，DGCI _app与叶片氮浓度之间的关系更加可变（R ²实验室测量时 ，DGCI_凸轮和叶片N浓度之间的差值= 0.33，0.69）。在野外条件下，DGCI_应用程序也比实验室中测得的DGCI _cam更易变。DGCI_凸轮和DGCI_应用程序之间的差异是因为DGCI_凸轮使用整个叶子进行颜色分析，而DGCI_应用程序仅使用叶子的中心部分进行颜色分析。