| The objective of this study was to provide a theoretical basis for real-time evaluating nitrogen nutrition and rational nitrogen fertilization of drip-irrigated winter wheat in Xinjiang Province, through a two year fixed position experiment by using the local popular variety Xindong 22 as material under five nitrogen application levels (0, 120, 240, 360 and 480 kg·hm-2).The models of nitrogen fertilizer recommendation of drip-irrigated winter wheat growing stages were constructed based on the analysis of the relationship between the application of nitrogen fertilizer and remote sensing indicators:NDVI and NDRE at different growth stages, which were measured using the portable active remote sensing spectrometer RapidScan CS-45 on canopy. The results showed that the values of NDVI and NDRE in drip-irrigated winter wheat canopy increased rapidly during the recovering stage and the booting stage, and during the booting stage and the filling stage.The values of NDVI and NDRE increased slowly, and they began to decrease after filling stage; the dynamic change trend of NDVI and NDRE in drip-irrigated winter wheat canopy is significantly consistent.In general, the values of NDVI and NDRE increased with the increase of nitrogen fertilizer application amount, and it presentsed a significant liner relationship between the value of spectral indices (NDVI and NDRE) and nitrogen fertilizer application at growing stages,NDVI was better than NDRE during the growth stages of recovering and flowering, and the r were 0.925 4 and 0.944 5, respectively. NDRE is better than NDVI during the growth stages of jointing, booting, filling and milking, and the r were 0.929 7, 0.959 6, 0.941 0 and 0.953 0, respectively. The total application rate of nitrogen fertilizer was 239.98 kg·hm-2 during the whole growth period of drip-irrigated winter wheat. The corresponding thresholds of NDVI at the growth stages of recovering, jointing, booting, flowering, grain filling and milking were 0.150 8, 0.721 3, 0.820 6, 0.828 8, 0.831 6 and 0.741 0, respectively. The corresponding thresholds of NDRE at the above six growth stages were 0.059 3, 0.242 5, 0.307 6, 0.346 5, 0.360 4 and 0.322 5, respectively. As a result, the recommended nitrogen application model based on canopy NDVI could be selected at the growth stages of recovering and flowering, and the recommended nitrogen application model based on canopy NDVI could be selected at the growth stages of jointing, booting and grain filling. |
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