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Use of Active Crop Canopy Reflectance Sensor for Nitrogen Sugarcane Fertilization

L. R. Amaral, G. Portz, H. Rosa, J. Molin

University of São Paulo

Researches about the use of ground-based canopy reflectance sensors aiming the nitrogen management fertilization on variable-rate over the sugarcane crop have been conducted in São Paulo, Brazil since 2007. Sugarcane response to nitrogen is variable, making difficult the development of models to estimate its demands. In this context, optical sensing has a great potential to evaluate and intervene in-season crop nutrition. Part of these studies is based at the CropCircle optical sensor (model ACS-210) and experiments have been conducted on plots set over in distinct growing conditions and nitrogen rates. The evaluations with the sensor are made according to the crop height. The relationship between yield and the vegetation indexes NDVI and CI were analyzed, in addition to the chlorophyll content (Minolta SPAD). Due to the variability of situations where sugarcane is cultivated, it was proposed the comparison of a specific algorithm for each situation ("N ramp") and a general algorithm ("N-rich strip"), aiming variable-rate nitrogen recommendation. The ideal moment to perform measurements with the optical sensor is when the crop is between 0.4 to 0.7 m height, before that there is not enough biomass, and after that, the sensor signal begins to saturate. During this moment, vegetation indexes showed high correlation with the nitrogen applied and the final yield, while for the chlorophyll content it did not happen all the time. The specific methodology showed contradictory results, assigning nitrogen in excess at fields that did not responded to this nutrient. The general methodology, working with relative values, was adequate, since a correct yield estimative is performed by producers to be introduced in the algorithm. The CropCircle optical sensor was efficient in determining sugarcane crop N needs, although several changes have to be undertaken on the methodologies of recommendation that have been studied for other crops around the world.

Keyword: Crop canopy sensor, nitrogen recommendations, Proximal Sensing

L. R. Amaral G. Portz H. Rosa J. Molin Proximal Sensing in Precision Agriculture Poster 2012

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