Early detection of canopy nitrogen deficiency in winter wheat (Triticum aestivum L.) based on hyperspectral measurement of canopy chlorophyll status

摘要

A spectroscopic method was developed to measure the nitrogen status of winter wheat (Triticum aestivum L.) canopies. Two years of field experiments, including a range of cultivars grown with differing levels of nitrogen fertilization, were conducted and ground-based hyperspectral data were collected to develop and validate an empirical model for early detection of low canopy chlorophyll content. Canopy reflectance was measured with a spectrometer, fitted with a 25° field of view fibre-optic adaptor. Canopy chlorophyll density (CCD), representing the total amount of chlorophyll present in the canopy per unit ground area, was combined according to the contribution of winter wheat leaves in different layers of the canopy and related to canopy reflectance. Combined canopy chlorophyll density (CCCD) calculated with both layers 1 and 2 and with layers 1, 2 and 3 were better related to difference vegetation index (DVI=R_(NIR)?R_(RED), where R_(NIR) and R_(RED) were reflectance at 890 nm and 670 nm, respectively) than CCD in any individual layer. Statistical prediction models of canopy chlorophyll status in winter wheat were developed. The CCCD_(1+2) model demonstrated lower root mean square errors and higher modelling efficiencies than those of the CCCD_(1) and CCCD_(1+2+3) models. Chlorophyll status in the two uppermost layers of the wheat canopy could be quantified using DVI. Therefore, early detection of canopy nitrogen deficiency in winter wheat was achieved.