|Chung, Sun-Ok -|
|Jung, Ki-Yuol -|
Submitted to: Journal of Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2011
Publication Date: March 31, 2011
Citation: Chung, S., Jung, K., Sudduth, K.A. 2011. Estimation of Korean paddy field soil properties using optical reflectance. Journal of Biosystems Engineering. 36(1):33-40. Interpretive Summary: Measuring the variation in soil properties within fields is an important component of precision agriculture. For many soil properties, it is difficult to obtain enough data to accurately characterize their spatial variation, due to the cost of traditional sampling and laboratory analysis. Sensors that can estimate soil properties without the need for sampling are a promising alternative. One technology that has received considerable attention in this regard is optical reflectance sensing in the visible and near infrared (NIR) wavelength bands. In this study, we examined the use of visible-NIR reflectance sensing to estimate a number of soil properties in Korean soils. We collected soil samples to approximately 2 ft. deep from fields with soils representing 74% of the total Korean paddy (rice) field area and measured their reflectance characteristics in the laboratory. We used statistical techniques to relate the reflectance to laboratory-measured soil properties. We found that visible-NIR reflectance gave good estimates of magnesium, calcium, and total carbon. For many other soil properties results were not quite as good, but were still acceptable. We also investigated what wavelengths were most important in the relationship, finding several wavelengths that were important contributors for multiple soil properties. This is an important finding because the need to sense only a few wavelengths could result in a more rugged, inexpensive, and reliable sensor than if the full spectrum were required. The results of this study will provide information that instrumentation engineers and researchers can use to develop new in-field soil sensing technology.
Technical Abstract: An optical sensing approach based on diffuse reflectance has shown potential for rapid and reliable on-site estimation of soil properties. Important sensing ranges and the resulting regression models useful for soil property estimation have been reported. In this study, a similar approach was applied to investigate the potential of reflectance sensing in estimating soil properties for Korean paddy fields. Soil cores up to a 65-cm depth were collected from 42 paddy fields representing 14 distinct soil series that account for 74 percent of the total Korean paddy field area. These were analyzed in the laboratory for several important physical and chemical properties. Using air-dried, sieved soil samples, reflectance data were obtained from 350 to 2500 nm on a 1.4 to 2 nm sampling interval with a laboratory spectrometer. Calibrations were developed using PLS (partial least squares) regression, and wavelength bands important for estimating the measured soil properties were identified. PLS statistics showed good estimations of Mg (R2 = 0.80), Ca (R2 = 0.77), and total C (R2 = 0.92); fair estimations of pH, EC, P2O5, K, Na, sand, silt, and clay (R2 = 0.59 to 0.72); and poor estimation of total N. Many wavelengths selected for estimation of the soil properties were identical or similar for multiple soil properties. More important wavelengths were selected in the visible-short NIR range (350-1000 nm) and the long NIR range (1800-2500 nm) than in the intermediate NIR range (1000-1800 nm). These results will be useful for design and application of in-situ close range sensors for paddy field soil properties.