Correções matemáticas da relação infravermelho/vermelho e do índice de vegetação da diferença normalizada para aplicação de nitrogênio em tempo real.

Abstract

The application of the precise amount of nitrogen needed has the potential to increase productivity in areas which previously were fertilized below crop need and to reduce unnecessary application in areas previously fertilized above crop need. Fertilizer application based on crop spectral characteristics is a promising approach to this problem. The objective of this work was to study how corn reflectance indices (near infrared/red and NDVI) were influenced by the hour of the day and sun angle, and the dependence of this relationship on row direction. Corn was planted in North-South and East-West-oriented rows and fertilized with 160 kg N/ha. Reflectance in four wavelengths was measured at stage V6 using a Crop Circle passive radiometer positioned over the same plants from sunrise to sunset. Row direction influenced the daily pattern of reflectance, which changed more in North-South rows. NDVI had a smaller coefficient of variation than near infrared/red, possibly making it more desirable for real time crop sensing to control nitrogen rate. Models developed to characterize the dependence of the indices on row direction, sun angle, and time of day had R2 values around 0.8, suggesting a good chance of improving system performance by correcting reflectance measurements for these effects.