Short-range-order minerals as powerful factors explaining deep soil organic carbon stock distribution: the case of a coffee agroforestry plantation on Andosols in Costa Rica

Abstract

Abstract. Soil organic carbon (SOC) constitutes the largest terrestrial C stock, particularly in the Andosols of volcanic areas. Quantitative information on distribution of SOC stocks is needed to construct a baseline for studying temporal changes in SOC. The spatial variation of soil short-range-order minerals such as allophane usually explains the variability of topsoil SOC contents, but SOC data for deeper soil layers are needed. We found that within a 1 km2 Costa Rican basin covered by coffee agroforestry, SOC stocks in the upper 200 cm of soil were highly variable (24 to 72 kg C m−2). Topsoil SOC stocks were not correlated with SOC stocks present in deeper layers. Diffuse-reflectance mid-infrared (MIR) spectroscopy made possible the analysis of a large number of samples (69 soil profiles, i.e. 598 soil samples) for ammonium-oxalate and sodium-pyrophosphate-extractable forms of Al, Fe, and Si, as well as SOC content and bulk density. Using the MIR spectra, we identified two different soil materials, which were identified as allophanic and halloysitic soil material. Allophanic soil occurred on top of the halloysitic soil. The thickness of the allophanic soil material, rich in SRO minerals and related to a young andic A horizon, explained the variability of SOC. This study illustrates that knowledge of topography and pedogenesis is needed to understand and extrapolate the distribution of SOC stocks at landscape scales.

Soil Organic Carbon Stock Variation under Different Soil Types and Land Uses in the Sub-Humid Noun Plain, Western Cameroon

“…These results are in agreement with those of Munoz-Rojas et al [47] and Chevallier et al [48] carried out in southern Spain and Costa Rica, respectively, where the coefficients of variation are well above 30% within the different soil types studied.…”

Soil organic matter storage in temperate lowland arable, grassland and woodland topsoil and subsoil

“…The reason suggested for this greater subsoil aggregate creation was because of a greater abundance of unsaturated mineral surfaces in the subsoil. Therefore, it is likely that sorption of SOM facilitates aggregation in the subsoil (Yu, Xiao, et al, 2017; Yu, Zhang, et al, 2017) and we expect that sorption, particularly to short‐range‐order minerals (Chevallier et al, 2019), will play a greater role than physical protection mechanisms in the subsoil.…”

Spatial-temporal variations of nitrous oxide emissions in coffee agroforestry systems in Costa Rica

“…Mean annual precipitation rate and mean annual air temperature (2009 -2018) were 2820 mm and 19.5 ºC with January to April being the driest months. The dominating soil type in study site I AEC is classified as an Andisol (Chevallier et al, 2019).…”