The effects of traditional rotational terrace agriculture in the high Andes on the dynamics of their soil organic matter

The mountain soils of the Andes, especially in the Puna ecoregion (above 3500 m elevation), have been shown to maintain disproportional soil carbon stocks derived from an abundance of soil organic matter (SOM). However, the mechanisms governing the stabilization of SOM in this understudied tropical high-alpine region remain elusive; in particular with respect to the interplay with human land management in the area. Here we present the results of a study in the Miraflores area of the Peruvian Andes where soils are cultivated on terraces under a rotational system that has been in place for 9,000 years. This system alternates 2-4 years of cultivation with 9-11 years of regeneration, In our study, we quantified soil carbon stocks in several soil carbon fractions—total organic carbon, labile carbon, soluble organic carbon—as well as associated aluminium, iron and calcium pools. Moreover, we examined the molecular composition of SOM under different land-use types within the region.

The results show pronounced differences in carbon accumulation and decomposition between terraced soils (cropped, cropped but outside the rotation, regenerating and abandoned terraces) and non-terraced soils (grazing land, natural grassland and peatland). We found the rotational crop management to exert a more beneficial effect on SOM accumulation and composition than continuous agriculture without rotation. The preservation of organic was driven primarily by land-use practices, plant-derived litter inputs and microbial activity, while soil mineralogy appeared to play only a minor role in carbon stabilization in this landscape.

Overall, our findings underscore the importance of sustainable land management in high-altitude ecosystems for strengthening carbon sequestration and reducing the impacts of climate change, particularly in highly susceptible mountain regions.