Detecting nitrogen deficiency on irrigated cash crops using remote sensing methods

Abstract

Early detection of nitrogen deficiency on annual agricultural crops can assist the management of N-fertilization to improve crop yields. Low altitude aerial photography is an inexpensive means to assess crop canopy radiation in the near infrared range. In this study, different Nitrogen experiments were laid out on cotton, tobacco and wheat. Nitrogen rates on the tobacco and cotton were 0.50, 100, 150 and 200 kg N ha1. On a wheat experiment the rates of N were 0.60, 120 and 180 kg N ha−1 with 4 times of application after planting. All these experiments were conducted in 1992 and 1996. Infrared aerial photographs and multi spectral videography were taken of the experiments at certain times using remotely piloted aircraft. These images were processed on a computer and classified into classes of high- and low-N categories using image processing software. A portable spectrometer operating in the 770 nm to 920 mn range was also used to assess N deficiency by measuring the reflected radiation of wheat canopies 70 days after planting. Interception of Photosynthetically Active Radiation (PAR) was used to assess the biomass of wheat over time. Light reflection in the near infrared wavelengths from airborne CIR photography and the 853 nm band from multi spectral videography correlated well with the N rates on the different crops. Spectrometric reflection provided the best detection of N-deficiency at the 779 nm wavelength. The PAR measurements followed the same correlation with N-rates. The results showed that CIR airborne photography, multi spectral videography and spectrometric reflectance provide a practical and economical means of assessing crop N status when standardized with an in-field reference. © 1999 Taylor & Francis Group, LLC.