Evaluation of Absolute Measurements and Normalized Indices of Proximal Optical Sensors as Estimators of Yield in Muskmelon and Sweet Pepper

The generally established protocol for leaf measurement with proximal optical sensors is to use the most recently fully expanded leaf. However, differences in nitrogen (N) status of lower and upper leaves could possibly be used enhance sensor measurement. Normalized indices that consider both have been proposed improve assessment crop N yield estimation. This study evaluated whether normalized improved estimation from measurements three different sensors: (i) SPAD-502 chlorophyll meter, (ii) Crop Circle ACS 470 canopy reflectance sensor, (iii) Multiplex fluorescence meter. was conducted sweet pepper (Capsicum annuum L.) muskmelon (Cucumis melo plastic greenhouses Almeria, Spain. Measurements were made on latest (most recent) (L1), second (L2), third (L3) fourth (L4) leaves. Yield models, using linear regression analysis, developed validated absolute sensors. Overall, calibration validation results indicated had better performance than all profiles. In species, there a at early phenological stages, such as vegetative flowering Absolute (L2, L3 L4) slightly compared L1 included L4 (L1–L4) those L2 (e.g., L1–L2 L1–L3). Of evaluated, Relative Index (RI), Difference (RDI), (NDI) very similar, superior (DI). this demonstrated did not estimation, performance.