Abstract
Precision nitrogen (N) management requires an accurate and timely in-season assessment of crop N status. The proximal fluorescence sensor Multiplex®3 is a promising tool for monitoring crop N status. It performs a non-destructive estimation of plant chlorophyll, flavonol, and anthocyanin contents, which are related to plant N status. The objective of this study was to evaluate the potential of proximal fluorescence sensing for N status estimation at different growth stages for rice in cold regions. In 2012 and 2013, paddy rice field experiments with five N supply rates and two varieties were conducted in northeast China. Field samples and fluorescence data were collected in the leaf scale (LS), on-the-go (OG), and above the canopy (AC) modes using Multiplex®3 at the panicle initiation (PI), stem elongation (SE), and heading (HE) stages. The relationships between the Multiplex indices or normalized N sufficient indices (NSI) and five N status indicators (above-ground biomass (AGB), leaf N concentration (LNC), plant N concentration (PNC), plant N uptake (PNU), and N nutrition index (NNI)) were evaluated. Results showed that Multiplex measurements taken using the OG mode were more sensitive to rice N status than those made in the other two modes in this study. Most of the measured fluorescence indices, especially the N balance index (NBI), simple fluorescence ratios (SFR), blue–green to far-red fluorescence ratio (BRR_FRF), and flavonol (FLAV) were highly sensitive to N status. Strong relationships between these fluorescence indices and N indicators, especially the LNC, PNC, and NNI were revealed, with coefficients of determination (R2) ranging from 0.40 to 0.78. The N diagnostic results indicated that the normalized N sufficiency index based on NBI under red illumination (NBI_RNSI) and FLAV achieved the highest diagnostic accuracy rate (90%) at the SE and HE stages, respectively, while NBI_RNSI showed the highest diagnostic consistency across growth stages. The study concluded that the Multiplex sensor could be used to reliably estimate N nutritional status for rice in cold regions, especially for the estimation of LNC, PNC, and NNI. The normalized N sufficiency indices based on the Multiplex indices could further improve the accuracy of N nutrition diagnosis by reducing the influences of inter-annual variations and different varieties, as compared with the original Multiplex indices.
Highlights
Nitrogen (N) is an essential nutrient for plant growth and development
During both the panicle initiation (PI) and stem elongation (SE) growth stages, the mean values of the Multiplex indices obtained using the OG mode were significantly higher (P ≤ 0.05) than the leaf-borne indices measured in the leaf scale (LS) mode, whereas the latter were significantly higher than the measurements obtained in the above the canopy (AC) mode
This research compared the LS, OG, and AC measurement modes of the fluorescence instrument Multiplex®3 and determined that the OG mode was best suited for this rice N status study
Summary
Nitrogen (N) is an essential nutrient for plant growth and development. excessive N fertilizer applications have led to severe environmental impacts in China [1,2]. There has been a growing interest in developing precision N management strategies in agricultural research for many years. This requires the development of efficient and timely crop N status diagnosis strategies and technologies [3]. Various instruments based on measuring chlorophyll have been developed to provide indirect, nondestructive, and real-time estimations of leaf N content [3,6]. Leaf chlorophyll absorbs red light but not infrared, the SPAD readings indicate plant chlorophyll concentration and N content [9,10,11]. The reliability of SPAD results is affected by factors such as growth stage, irradiance, water status, and leaf thickness [3,5,9]
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