Preston Sorenson | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Preston Sorenson. This seminar is open to the general public to attend.
Thesis Topic: Quantifying the Spatial Distribution of Soil Organic Carbon and Nitrogen Using Reflectance Spectroscopy

PhD with Dr. Sylvie Quideau.

Seminar Abstract:

Soil is a critical component of global biogeochemical cycles, and there is an increasing need for cost effective tools to measure soil carbon stocks and determine soil nitrogen contents. Reflectance spectroscopy can deliver large volumes of soil carbon data, with potential applications for understanding soil carbon distribution and assessing reclaimed soils. Reflectance spectra were collected on a range of soil samples, including intact cores, using a SisuROCK automated hyperspectral imaging system in a laboratory setting, focused on the shortwave infrared portion of the electromagnetic spectrum. Samples were also analyzed for soil organic carbon and total nitrogen concentrations by dry combustion to prepare a training data set to use as inputs for predictive models.  Predictive models were built using continuous wavelet processing along with Cubist and Bayesian Regularized Neural Net models. Overall, soil organic carbon was more aggregated in Chernozemic soils and in B and C horizons compared to A horizons. Nitrogen in turn showed more aggregation for all soil types and horizons compared to soil organic carbon. Additionally, crop rotations were revealed to influence both the concentration and distribution of carbon and nitrogen. Continuous forage rotations were found to have the highest soil organic carbon (SOC) and total nitrogen (TN) contents compared to an agro-ecological rotation for only the top 3 and 4 cm, respectively. These two rotations had comparable concentrations for both parameters for the rest of the topsoil, which was greater than the concentration of SOC and TN in a continuous grain rotation to depths of approximately 12 cm. Increases in both SOC and TN were associated with increased spatial aggregation at fine spatial scales. Overall, these results indicate that imaging spectroscopy can be used to investigate soil carbon and nitrogen, and their distributions, at fine spatial scales.