Spectral responses to labile organic carbon fractions as useful soil quality indicators across a climatic gradient

Authors: RAMIREZ, PAULINA - University Of Catolica De Chile; Calderon, Francisco; FONTE, STEVEN - Colorado State University; SANTIBANEZ, FERNANDO - University Of Catolica De Chile; BONILLA, CARLOS - University Of Catolica De Chile

Submitted to: Ecological Indicators
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2019
Publication Date: 4/1/2020
Citation: Ramirez, P., Calderon, F.J., Fonte, S., Santibanez, F., Bonilla, C. 2020. Spectral responses to labile organic carbon fractions as useful soil quality indicators across a climatic gradient. Ecological Indicators. 111:106042. https://doi.org/10.1016/j.ecolind.2019.106042.
DOI: https://doi.org/10.1016/j.ecolind.2019.106042

Interpretive Summary: In this study, a geographically diverse set of soils from South America were studied for their soil organic matter chemistry. The soil chemical composition was the related to the type of land use and geographic location where the soils were obtained. Our results show that the fragility of the soil carbon is related to aridity, with more humid soils having proportionately more easy to degrade soil organic matter. In addition, agricultural soils under semiarid agriculture, which have historically been more prone to C stock losses, show specific soil organic chemical characteristics that can be explained in the context of soil C losses over time.

Technical Abstract: Labile organic matter is an important indicator for evaluating the early impacts of agricultural management practices on soil quality. Light fraction organic matter (LFOM) and the permanganate-oxidizable C (POXC) are gaining notoriety as useful indicators of labile soil organic matter (SOM). However, the mechanisms that affect the amount and composition of labile fractions and their relationship with SOC content at regional scales are poorly studied. We measured the POXC and LFOM of 75 sites under different climate regimes in Chile. Topsoil was analyzed for total C and N content, aggregate stability, and texture. Additionally, the spectral properties of LFOM and whole soils were analyzed using diffuse reflectance Mid-infrared spectroscopy (MidIR). Our results show that labile fractions, POXC and LFOM, are related but influenced differently by climate. LFOM spectral responses showed differences across climates, in addition, the chemical properties of LFOM were more associated with O-alkyl C in cooler and rainy areas, and a relative accumulation of aromatic structures was found in warmer areas. In addition, we also found a positive relationship among SOC, POXC, soil aggregation and aliphatic functional groups in colder areas. In warmer areas, the stabilization of aliphatic compounds was found to be closely related to clay minerals. This study represents an important advancement in our understanding to elucidate vulnerability to SOC losses and mechanisms for SOC stability on a wide geographic scale.