Remotely assessing photosynthetic nitrogen use efficiency with in situ hyperspectral remote sensing in winter wheat

• Published in: European journal of agronomy 2018-11, Vol.101, p.90-100
• Main Authors: Zhang, Hai-Yan, Ren, Xing-Xu, Zhou, Yi, Wu, Ya-Peng, He, Li, Heng, Ya-Rong, Feng, Wei, Wang, Chen-Yang
• Format: Article
• Language: English
• Subjects: cultivars; developmental stages; Estimation model; field experimentation; Hyperspectral remote sensing; leaves; nitrogen; nitrogen fertilizers; nutrient use efficiency; photosynthesis; Photosynthetic nitrogen use efficiency; plant density; rapid methods; reflectance; remote sensing; screening; vegetation index; Winter wheat
• ISSN: 1161-0301; 1873-7331
• DOI: 10.1016/j.eja.2018.08.010

•A novel index (N efficiency index, NEI) successfully predicted photosythetic nitrogen use efficiency (PNUE).•The novel index can be presented as  1.8+R680R850×R760+R680R850+R680 , and it reduced soil and leaf cluster effects.•NEI enable different stage datasets (vegetative and reproductive stages) to be modelled uniformly.•NEI exhibited a superior predictive capacity for PNUE when compared with the common indices.•NEI accurately estimated PNUE of wheat across experimental conditions using remote sensing. Non-destructive and rapid methods for estimating nitrogen efficiency are helpful in quantifying and communicating the N use efficiency (NUE) in agricultural production. To accurately evaluate NUE, we analysed the quantitative relationship between leaf photosynthetic nitrogen use efficiency (PNUE) and wheat NUE, and investigated the quantitative relationship between PNUE and hyperspectral indices in winter wheat. Our field experiments were carried out during 2013–2016 across different growth stages, cultivars, planting densities, nitrogen (N) rates, and water treatments, and a nitrogen efficiency index (NEI) was developed to evaluate PNUE. Three of eight previously developed vegetation indices (VIs) performed well when regressed against PNUE; however, they exhibited bias between vegetative and reproductive stages. The NEI was obtained by integrating the reflectance at the red band (680 nm) into simple ratio index (SR (760,850)), to become a modified simple ratio index (mSR (760,850,680)), then we added a floating coefficient [1.8 + (R680/R850)] to mSR (760,850,680). Our novel index was better related with PNUE than previous VIs under different experimental conditions. There was no significant difference in the slope and intercept under the five experimental factors, suggesting that the new index is a superior tracker for PNUE changes under heterogeneous field conditions. These models accurately estimated PNUE in winter wheat, providing a theoretical basis and technical support for N fertilizer assessment and screening of N efficient wheat varieties.