Rational utilization of nitrogen fertilizer is one of the key factors to reduce production cost while improve the production of crops.The authors have developed a device for measuring the normalized difference vegetation index(NDVI) by using four specially designed photoelectric detectors;the NDVI can reflect the growing information and seasonal nitrogen fertilizer requirement of crops

and offers guidance for rational application of nitrogen fertilization.After calibration in laboratory

the measuring device needs no further correction.Experiments in National Engineering Research Center for Information Technology in Agriculture and National Laboratory of Color Science and Engineering indicate that the measurement technology can directly acquire NDVI

and that the measurement deviation is less than 5% compared with that measured by using ASD FR2500.