Environmental controls and long-term changes on carbon stocks under agricultural lands

Authors: RAMIREZ, PAULINA - University Of Catolica De Chile; Calderon, Francisco; FONTE, STEVEN - Colorad0 State University; BONILLA, CARLOS - University Of Catolica De Chile

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2018
Publication Date: 11/22/2018
Citation: Ramirez, P., Calderon, F.J., Fonte, S., Bonilla, C. 2018. Environmental controls and long-term changes on carbon stocks under agricultural lands. Global Change Biology. 186:310-321. https://doi.org/10.1016/j.still.2018.10.018.
DOI: https://doi.org/10.1016/j.still.2018.10.018

Interpretive Summary: We sampled a geographically diverse set of sites in Chile and measured the soil carbon content. Our data was compared to an older data set in order to quantify fluctuations in soil C stocks. The sample set included soils from different climates and different soil types. Our results show that Mollisols suffered net C losses, Mollisols typically develop in semi-arid areas under grassland cover, but those in our study have been subject to cultivation in recent times. Because of this, we hypothesize that agricultural soils in semiarid climates are particularly vulnerable to C loss, and we propose that the balance of plant productivity, microbial decomposition, and soil mineralogy all play a role in the soil C dynamics.

Technical Abstract: Improved understanding of large-scale changes in soil organic carbon (SOC) stocks is critical for developing management strategies that ensure effective climate change mitigation and the long-term productivity of soils around the globe. Changes in SOC are likely to vary across different soil and climate conditions, yet long-term data to elucidate these trends across different types of ecosystems remains limited. In this study we evaluated long-term changes in SOC across a gradient of climate conditions (from arid to hyper humid) and soil orders (Andisols, Mollisols, Inceptisols, Histosols, Alfisols, and Ultisols) in central Chile. Soils for this study were sampled between 2014 and 2016 and analyzed for total C and N content, aggregate stability, soil texture, bulk density, pH as well as spectral properties, using mid-infrared (MidIR) and near-infrared spectroscopy. SOC stocks were compared to those previously measured at the same sites between 1972 and 1994, covering a wide range of SOC values (from 12 Mg C ha-1 to 128 Mg C ha-1). Our findings suggest that the largest SOC losses occurred in semiarid and subhumid areas for the time frame considered, decreasing from their initial C stocks by 24.2% and 26.1%, respectively. In cooler and more humid regions, SOC stocks were stable or increased over time. Among soil orders, Mollisols showed the largest losses in SOC across soil types, with a 29.9% reduction between sampling dates. The MidIR results indicate that the mineral bands for clays and silicates were associated with sites demonstrating SOC conservation, suggesting that mineral protection played an important role in the long-term SOC trends. Cultivated soils in semiarid regions appeared to be more vulnerable than those in arid regions, mainly because of soil mineral features, where the increase in soil moisture and high temperature seem to promote the C mineralization.