NPK detection using LED based spectroscopy on soil

Abstract

xSoil spectroscopy measurement is widely used to determine the macronutrient level in soil. This measurement is useful to assist the quality controls of agricultural production, soil fertility and would also helpful in reducing the agricultural cost. This paper details the preliminary optical characterization of soil spectroscopy for the monitoring of soil macronutrient concentration. By using a wavelength corresponding to a macronutrient absorption peak, the Beer -Lambert Law can be used to relate the concentration of macronutrient surrounding the sensing portion to the amount of absorbed light. Based on the peak absorbance level performance, LED wavelengths have been identified in replacing the deuterium and halogen lamps in visible and near infrared wavelength for the concentration measurement of soil macronutrient. The chosen LEDs are in a range from 400nm to 1100nm. From colour reagent, the amount of macronutrient can be detected by observing the intensity of colour -develop solution. This colour -develop solution, then illuminates by deuterium and halogen lamp to measure the peak absorbance . The soil samples have obtained the peak absorbance level for nitrogen and phosphorus at wavelength of 450nm and 780nm respectively . The experimental result shows the absorption line for measured potassium is in a similar pattern, but the maximum absorbance shows in range 400nm to 500nm . By using LEDs, nitrogen, phosphorus and potassium are estimated to absorb blue, red and near -infrared wavelength range respectively for all samples. Future work would be carried out to study the soil spectroscopy measurements using LEDs and photodetector in order to replace the spectrometer usage for soil spectroscopy. This would lead to achieving the primary objective of this research in developing a simple and low cost spectroscopy uses light -emitting diode (LED).