INFLUÊNCIA DA DIREÇÃO DA SEMEADURA E DA HORA DO DIA EM ÍNDICES DE VEGETAÇÃO

There is high spatial variability of nitrogen availability within the same area. Supplying the required N can increase income, and reduce unnecessary N supply and its leaching to underground water. Measuring spectral reflectance and calculating vegetation indexes is considered promising non-destructive and non-contact approach to instantly measure N deficiency in corn. This study was done to determine the influence of the direction of the sowing and of the hour of the day on determination of the vegetation indexes of corn crop. The sowing lines followed North-South and East-West direction. The sowing direction and sun trajectory influenced the indexes: the NIR/red ratio, the Normalized Difference Vegetation Index (NDVI), the Soil-Adjusted Vegetation Index (SAVI), the Optimized Soil-Adjusted Vegetation Index (OSAVI), the NIR/green ratio and the Green Normalized Difference Vegetation Index (GNDVI). GNDVI was more homogeneous with lower coefficient of variation, thus appears to be more appropriate for use in real time N application and in variable rates, when control of sowing direction is not possible. In other cases SAVI and OSAVI are the more suitable as their models had higher R2.