VNIR Spectroscopy Estimation of Soil Quality Indicators

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

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 11/18/2008
Publication Date: 6/21/2009
Citation: Sudduth, K.A., Kitchen, N.R., Kremer, R.J. 2009. VNIR Spectroscopy Estimation of Soil Quality Indicators. ASABE Annual International Meeting Technical Papers. ASABE, St. Joseph, Michigan. Paper No. 097019. Available: http://asae.frymulti.com/azdez.asp?search =1&JID=5&AID=27285&CID=reno2009&v=&i=&T=1

Interpretive Summary: Much of the claypan soil area of the U.S. Midwest has been under cultivation for only about a century. However, because these soils were vulnerable to water erosion, soon after the grasslands were plowed they lost topsoil, a critical component for plant nutrients and soil water storage, which are important aspects of soil quality. In general, soil quality is a broad concept that includes a soil’s ability to grow plants and respond to current management practices so there is minimal negative impact to the environment. For claypan soils, decreased soil quality caused by erosion is not uniform over fields. Therefore, we are researching precision conservation systems that target soil-building management to those portions of fields that most need soil quality improvement. The purposes of this research were (1) to evaluate soil quality differences three years after initiation of a precision conservation system on a claypan-soil research field and (2) to evaluate the ability of optical soil reflectance techniques to detect these differences. With laboratory analysis, we were able to detect improvement in some of the measured soil quality indicators related to soil organic matter. However, the optical sensing methods were not accurate enough to reliably detect changes in soil quality indicators. Most other optical sensing studies have examined soils from multiple locations or contrasting management, and therefore have had more soil variation. Although our optical methods were as sensitive as those in these other studies, the within-field variation we were trying to detect in soil quality indicators was much smaller. Regardless of the lack of optical detection, the fact that laboratory methods were able to detect soil quality differences within three years of a management change is an important finding. The results of this research indicate that our precision conservation approach can provide soil quality benefits on claypan soil fields, although additional assessment will be needed after more time has passed. This type of information is important to provide a basis for future management strategies that will be helpful in developing sustainable food, fuel, and fiber production systems.

Technical Abstract: 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 purposes of this research were (1) to evaluate changes in soil quality indicators after initiation of a precision conservation system on a typical claypan-soil research field in northeast Missouri and (2) to evaluate the ability of visible and near infrared (VNIR) spectroscopy to estimate those soil quality indicators. Soil samples were obtained to a 15-cm depth on a 30-m grid spacing, plus at a number of random sampling locations, before and three years after conversion from a corn-soybean rotation to a no-till soybean-wheat-hay rotation. Laboratory analyses were conducted for potential indicators of soil quality, including chemical constituents, labile and total organic carbon, and particulate organic matter carbon (POM-C) and nitrogen (POM-N). VNIR reflectance of dried and sieved samples was obtained in the laboratory using a spectrometer with a wavelength range from 350 to 2500 nm. Calibrations of VNIR reflectance to soil quality parameters were accomplished using partial least squares regression. Laboratory analysis showed a significant increase in soil quality indicator values over the study period, particularly POM-C and POM-N. These increases were greatest in the wetter, lower-landscape portions of the field, perhaps due to higher biological activity. VNIR spectroscopy was not able to accurately estimate the soil variables studied, with the exception of pH. This may have been due to their relatively low variability across the study area. Additional research is planned to evaluate VNIR spectroscopy for estimating soil quality indicators across multiple management systems where variability is expected to be greater.