This study aimed to evaluate, under field conditions, the effect of variation in levels of nitrogen fertilization on the detection of nitrogen content in cotton (Gossypium hirsutum L. var. latifolium Hutch) leaves using reflectance properties registered by an active optical sensor. The experiment was conducted in randomized blocks and treatments consisted of five levels of nitrogen (0, 50, 100, 150 and 200 kg of N ha-1) with four replications. Normalized Difference Vegetation Index (NDVI) and the ratio Red/Near infrared (RED/NIR) data were collected 23 to 92 days after the emergence (DAE), with the total of 9 dates. Data referring to the chlorophyll index, leaf area index (LAI) and plant height were also collected. The values of NDVI presented a tendency to increase along the period, while Red/NIR presented an inverse trend, being significantly affected by the rates of applied N starting from 45 DAE. At 92 DAE, NDVI presented a positive linear relationship with N contents of leaves. Significant relationships were observed between the values of NDVI and chlorophyll index and LAI. The sensor may be a potential tool for nitrogen deficiency detection in cotton.
precision agriculture; NDVI; nutritional state
