Abstract
Accurate assessment of crop nitrogen (N) status and understanding the N demand are considered essential in precision N management. Chlorophyll fluorescence is unsusceptible to confounding signals from underlying bare soil and is closely related to plant photosynthetic activity. Therefore, fluorescence sensing is considered a promising technology for monitoring crop N status, even at an early growth stage. The objectives of this study were to evaluate the potential of using Multiplex® 3, a proximal canopy fluorescence sensor, to detect N status variability and to quantitatively estimate N status indicators at four key growth stages of maize. The sensor measurements were performed at different growth stages, and three different regression methods were compared to estimate plant N concentration (PNC), plant N uptake (PNU), and N nutrition index (NNI). The results indicated that the induced differences in maize plant N status were detectable as early as the V6 growth stage. The first method based on simple regression (SR) and the Multiplex sensor indices normalized by growing degree days (GDD) or N sufficiency index (NSI) achieved acceptable estimation accuracy (R2 = 0.73–0.87), showing a good potential of canopy fluorescence sensing for N status estimation. The second method using multiple linear regression (MLR), fluorescence indices and GDDs had the lowest modeling accuracy (R2 = 0.46–0.79). The third tested method used a non-linear regression approach in the form of random forest regression (RFR) based on multiple sensor indices and GDDs. This approach achieved the best estimation accuracy (R2 = 0.84–0.93) and the most accurate diagnostic result.
Highlights
Nitrogen (N) is one of the most important macronutrients for crop growth that strongly influences crop photosynthesis and gross primary productivity [1,2]
According rates at each growth stage, the effect of N fertilization treatment on most of the individual signals was wasnot notsignificant significantwhereas whereasthe the opposite was true fluorescence indices signals opposite was true for for the the fluorescence indices calcalculated from the individual signals
This study examined and verified that the fluorescence sensor Multiplex is a promising tool for N variability detection and N nutritional status estimation in maize
Summary
Nitrogen (N) is one of the most important macronutrients for crop growth that strongly influences crop photosynthesis and gross primary productivity [1,2]. Inappropriate N fertilization can reduce crop yield due to N deficiency or lead to negative environmental impacts due to N surplus [3,4,5]. It is imperative and necessary to assess the N status effectively and understand crop N demand to guide producers to make proper N management decisions. The methods for determining crop N status have been intensely studied and thoroughly discussed. The traditional laboratory wet-chemical methods to determine N concentration in crops are based on destructive sampling and are labor-intensive and time-consuming. To overcome these shortcomings and realize high efficiency in modern agriculture, sensing technology has shown great potential in assessing crop N status
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