Proximal Soil Reflectance and Fluorescence Sensing for Soil Fertility Assessment.

Precision agriculture aims at optimizing input rates at every locations of the field. Optimal input rates usually depend on information coming from both soil and crop. The level of precision with which a farmer can manage is crop is contingent upon the level of precision with which he characterizes it. Soil samples represent a good way to measure soil fertility and are widely used to create input prescription maps. However, the spatial range, which consist of the distance beyond which the information from the soil sample is no longer correlated, of most soil parameters is far shorter than the distance between soil sample locations. This prevents the reliable use of spatial interpolation techniques to estimate soil parameters values at every location of the field. Optical characteristics of soil such as reflectance and fluorescence have the potential to provide reliable estimates of soil physical and chemical properties at a high resolution. The hypothesis of this project was that soil reflectance and induced fluorescence can be used to estimate soil fertility. About 200 soil samples were collected in several fields located in Colorado, USA. At each soil sampling location, induced fluorescence was acquired in situ using the Multiplex3® fluorescence sensor. Results have demonstrated that several soil properties are correlated with soil reflectance and fluorescence parameters. These results pave the way for a new set of sensor for proximal soil sensing using optical properties.