Observing change in potassium abundance in a soil erosion experiment with field infrared spectroscopy

Soil erosion has been studied extensively in the last decades. Studies on soil particle movement through chemical tracers were mostly based on the use of radioactive elements. These however have a limited half-life, and are highly toxic and expensive to measure over large areas. This study examines the possibility to use Potassium (K), in the form of an agricultural fertilizer, as a soil particle tracer. Soluble Potassium is spectrally active and has an absorption feature near 2465 nm. This research hypothesises that flowing water moves surface soil particles with adsorbed K and can be traced by observing the change in absorption feature. A field-based water flow experiment was conducted on 3 plots in silty loam soils in the Netherlands. Two plots were treated with 0.6 and 2.48 mg/g of K2O fertilizer, and one plot was used as reference. Infrared reflectance spectra were collected to observe spatial variation in available K, before and after application of fertilizer, and after runoff simulation by water flow. Change in absorption feature depth near 2465nm was used to determine K abundance, and maps with K distribution were produced for each stage of the experiment. Laboratory analysis was done to validate and explain the field results. Statistical relationships between absorption feature parameters of K, water and clay were established to determine whether K was removed during the experiment. Based on coefficients of determination (R2), it can be concluded that an increase in moisture and clay content in a soil of over 18% poses a practical limitation in the use of K as a soil particle tracer with field infrared spectroscopy.