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Page 4 of 23 Diaz-Vallejo et al. Carbon Footprints 2026, 5, 12

these objectives frame a core question of whether SOC variability in tropical agroecosystems is better
interpreted through context-specific benchmarks that account for soil and climatic heterogeneity rather than
reference-based approaches.

METHODS
A case study: Puerto Rico
The Caribbean Area Natural Resources Conservation Service (NRCS) has identified soil health as a priority
for improving agricultural productivity and reducing soil erosion in Puerto Rico . Historically, the island
[35]
experienced extensive deforestation for agriculture and livestock, with approximately 78% of land cleared
during the 1900s . During the 20th century, massive migration and economic shifts toward industrial and
[36]
service sectors led to widespread agricultural land abandonment . Today, about 42% of Puerto Rico’s land is
[37]
identified as suitable for agricultural production , including 23% for row crops, livestock, dairy, hay, and
[38]
fruits, and 19% for forestry and agroforestry activities. In Puerto Rico, transitions among these land uses may
have altered organic matter inputs, soil structure, and biogeochemical processes, leading to persistent
legacies in SOC that vary across soil types and climatic gradients. As a result, present-day SOC patterns
reflect not only current land use but also cumulative effects of historical land management and recovery
trajectories, representing conditions observed in other tropical landscapes.

Puerto Rico, located between 17°45’ and 18°30’N and 65°45’ and 67°15’W, covers approximately 8,740 km .
2
The island exhibits sharp climatic gradients, from dry semi-deciduous forests in the southwest to moist and
wet forests in the northeast, and an elevation range from sea level to 1,338 m at Cerro de Punta. The climate
is tropical maritime , with mean annual temperatures ranging from 20 °C in high elevations to 26 °C in
[39]
coastal areas and mean annual precipitation spanning 850-4,500 mm. These strong climatic gradients,
combined with complex topography and soil diversity, provide the opportunity to assess environmental
effects on SOC under different land uses.

The island’s soils encompass 10 of the 12 USDA soil orders (Alfisols, Entisols, Histosols, Inceptisols,
Mollisols, Oxisols, Ultisols, Vertisols, Aridisols, and Spodosols). The coexistence of the diversity of soils
within a relatively small area reflects the interaction of steep climatic gradients, diverse parent materials,
variable drainage conditions, and long-term weathering across contrasting geomorphic settings on the island
providing a space for a range of soil representations in the region [40,41] . This diversity provides an excellent
context for examining SOC dynamics across contrasting environments.

Data collection
A regional SOC dataset was assembled by integrating data from multiple sources, including pedon analyses
from the USDA NRCS and published research studies in the literature. From the NRCS Soil Characterization
Database, we retrieved 234 pedons analyzed by the Kellogg Soil Survey Laboratory in Lincoln, NE using the
SoilDB package in R . For each pedon, we extracted latitude, longitude, soil series, soil order and suborder,
[42]
SOC concentration (%), and particle-size fractions (% sand, % silt, % clay). Land use was determined by
overlaying pedon coordinates with the 2001 National Land Cover Database (NLCD) in Google Earth Engine.
The NLCD classes were reclassified into five land-use categories: agriculture (cultivated crops), pastures
(pasture, hay, and herbaceous lands used for grazing), forests (evergreen and woody vegetation), rangelands
(herbaceous and shrubby vegetation), and wetlands (emergent herbaceous wetlands). We complemented the
NRCS data with 352 pedons compiled from published studies that included SOC concentration, land use,
geographic coordinates, soil order, and textural information for sites in Puerto Rico [7,34,43] .

Soil orders and suborders were verified using the Taxonomic Classification of the Soils of Puerto Rico to
[41]
ensure consistency with updated Soil Taxonomy classifications, as soil classifications have been revised since