Soil organic carbon balance across contrasting plant cover ecosystems in the Peruvian Amazon

Geomar Vallejos-Torres1*, Nery Gaona-Jimenez1, Andi Lozano1, Christopher I. Paredes1, Carlos M. Lozano1, Alberto Alva-Arévalo1, Jorge Saavedra-Ramírez2, Luis A. Arévalo2, Keneth Reategui3, Wilfredo Mendoza4, Juan R. Baselly-Villanueva5, and César Marín6, 7
The Peruvian Amazon has been significantly affected by land use and climate change, decreasing decomposition processes, which cause a significant depletion of soil C stocks. In this study, we estimated soil organic C (SOC) mediated by different plant covers in coffee (Coffea arabica L.) plantations and secondary forests in several districts of the San Martín Region, Peru. We calculated the critical threshold, saturation point, and the organic C deficit of these Amazonian soils. The association between geography, soil physical-chemical characteristics, and SOC was estimated through principal component analysis. Across all sites of the study, SOC stock had an average value of 69.19 t ha-1, with 48.95 t ha-1 constituting inorganic C. The highest SOC stock (225.28 t ha-1) was observed under secondary forest in the Jepelacio district. The SOC stocks were positively correlated with altitude and CaCO3 content only in secondary forests. The current measured amount of organic C within 15 cm soil depth was 28.5 g C kg-1, which is very low and close to the critical threshold (20.6 g C kg-1) -estimated based on its clay and silt contents. Our SOC stocks measurements indicated a worrisome situation, as they are close to the critical threshold, which exposes this area to a greater and stronger degradation.
Keywords: Coffea arabica, critical threshold, forestry soil, Peru, plant cover, saturation point, SOC deficit.
1Universidad Nacional de San Martín, Tarapoto, San Martín, Perú.
2Universidad Nacional Autónoma de Alto Amazonas, Loreto, Perú.
3Universidad Nacional Intercultural de la Amazonía, Pucallpa, Perú.
4Universidad Católica Sedes Sapientiae, Jr. Esq. Constelaciones y Sol de Oro, Los Olivos, Lima, Perú.
5Instituto Nacional de Innovación Agraria - INIA, Maynas, Loreto 16430, Perú.
6Universidad Santo Tomás, Centro de Investigación e Innovación para el Cambio Climático (CiiCC), Valdivia, Chile.
7Vrije Universiteit Amsterdam, Faculty of Earth and Life Sciences, Amsterdam, The Netherlands.
*Corresponding author (gvallejos@unsm.edu.pe).