[Nitrogen status diagnosis of summer maize by using visible spectral analysis technology]

In the present paper, a field experiment with different N rates was conducted to study the possibility of using the visible spectrum of crop canopy to diagnose N status for the summer maize. Visible spectrum parameters were compared with the leaf SPAD readings, total N concentration and vein nitrate concentration. Field measurement data showed that the greenness intensity, blueness intensity, normalized redness intensity, normalized greenness intensity and normalized blueness intensity of the maize canopy have significant relationships with leaf SPAD readings, total N concentration and vein nitrate concentration (under a low N input condition, with vein nitrate concentration < 2 000 mg x L(-1)) at summer maize 10 leaves unfold stage. The greenness intensity, blueness intensity, normalized greenness intensity and normalized blueness intensity have significant relationship with the vein nitrate concentration under a low N input condition (vein nitrate concentration < 2 000 mg x L(-1)). But when the maize vein nitrate concentration is above 2 000 mg x L(-1), there is no spectral parameter showing significant relationship with the vein nitrate concentration. The visible spectrum parameters reached a plateau with the vein nitrate concentration increasing. To sum up, the normalized greenness intensity (NGI) and normalized blueness intensity (NBI) have higher r values (0.45-0.66) than other parameters.