Estimating soil quality indicators with diffuse reflectance spectroscopy

Authors: Sudduth, Kenneth - Ken; Kremer, Robert; Kitchen, Newell; Myers, David

Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/25/2012
Publication Date: 7/15/2012
Citation: Sudduth, K.A., Kremer, R.J., Kitchen, N.R., Myers, D.B. 2012. Estimating soil quality indicators with diffuse reflectance spectroscopy. International Conference on Precision Agriculture, July 15-18, 2012, Indianapolis, Indiana. 2012 CDROM.

Interpretive Summary: Knowledge of within-field spatial variability in soil quality indicators is important to assess the impact of site-specific management on the soil. Standard methods for measuring these properties require considerable time and expense, so sensor-based approaches would be useful. The purpose of this research was to evaluate the ability of visible and near infrared (VNIR) diffuse reflectance spectroscopy (DRS) to estimate soil properties that are candidate soil quality indicators. Soil samples were obtained from two depths (0-5 and 5-15 cm) at a long-term (since 1991) experimental site in central Missouri where cropping systems were replicated across a typical claypan soil landscape. Laboratory analyses were conducted for potential indicators of soil quality, including soil organic carbon, soil glucosidase enzyme activity, and plant available nutrients. VNIR-DRS data were obtained in the laboratory using a spectrometer with a wavelength range of 350 to 2500 nm and calibrations to soil properties were developed with partial least squares regression. Results showed that VNIR DRS has potential to estimate several key soil quality indicators (SQI), including soil organic carbon, total soil nitrogen, glucosidase activity, and pH. However, other key SQI, such as aggregate stability, plant available nutrients, and nitrate and ammonia forms of nitrogen were not successfully estimated by this technology. Thus, a sensor fusion approach, combining VNIR DRS with other technologies, would likely be needed for implementing a sensor-based soil quality index.

Technical Abstract: Rapid estimation of soil quality is needed for determining and mapping soil variability in site-specific management. One technology that can fulfill this need is diffuse reflectance spectroscopy, which measures light reflected from the soil in the visible and near infrared wavelength bands. Reflectance spectroscopy has potential to replace traditional laboratory testing, which is often slow and expensive. The goal of this study was to use reflectance spectroscopy to detect soil properties that affect soil quality, including soil organic carbon, total nitrogen, plant available nutrients, and measures of microbial activity. Soil samples were taken from plots where different management systems were established in 1991 and where soil quality differences were found in previous studies. These samples were scanned with a laboratory spectrometer, and relationships between spectra and soil quality variables were examined. Estimates were quite good for soil organic carbon, total nitrogen, microbial activity, and pH, all variables that have been used as soil quality indicators. Other factors were not as well estimated. These results show that reflectance spectroscopy can provide some of the information important for estimating soil quality. This has the potential to benefit scientists and professionals who need more efficient methods to assess soils.