Electronic Sensing of Soil Organic Matter

A system has been developed which estimates total carbon content in the soil by sensing reflected light. Two sources of light were used. The first was a 6-V 150-mW incandescent lamp, reflected light being sensed by a silicon phototransistor. The second source was a light-emitting diode that emitted primarily in the infrared. Reflected light from this source was detected by a phototransistor sensitive to infrared. For the incandescent system, using 18 soils from the Mississippi Delta region of Arkansas, the coefficient of determination (r2) between the intensity of the reflected light and the soil carbon content was 0.75. Using the infrared system and the same soils, r2 was 0.70. In addition, a multiple linear regression based upon both of the sensors yielded an r2 of 0.75