Characterization of Soil Health in Colombian Coffee Farms.

Developing global standards for soil health (SH) is important for overcoming barriers established by differences in assessment protocols. This study was conducted to develop local SH standards specific to Colombian coffee farms, and to compare them to standards in the Northeast, USA and Western Kenya. A total of 223 soil samples were collected from coffee farms in Cauca, Colombia. Samples were analyzed for 10 SH indicators including wet aggregate stability (WAS), available water capacity (AWC), active carbon (AC), organic matter (OM), protein, respiration, pH, phosphorus (P), potassium (K) and minor elements (Mg, Mn, Fe and Zn). Samples were scored for SH using four different scoring frameworks: the Comprehensive Assessment of Soil Health (CASH), the Western Kenyan scoring functions, the Adjusted Colombian Soil Health Scoring Framework (A-CSHSF) and the Weighted Colombian Soil Health Scoring Framework (W-CSHSF), with the latter two being the research-specific regionally-adjusted scoring functions, developed from a combination of average local conditions and indicator thresholds found in the literature. While the A-CSHSF computed the overall SH score as the unweighted mean of all the individual indicator scores, the W-CSHSF assigned weights for each individual indicator as determined by a principal component analysis (PCA) for the SH indicator measurements. In the second part of the study, we were interested in defining a more simplified version of the A-CSHSF- the Simplified Colombian Assessment of Soil Health (S-CASH) that can be more affordable and accessible to Colombian subsistence farmers. A best subsets regression (BSR) was performed on the measured soil health indicators in addition to % sand, silt and clay, to determine the indicators and their groupings with the most predictive power of overall soil health. Results from the comparison of average scores revealed that the four scoring mechanisms generated significantly different indicator and overall SH scores. The Comprehensive Assessment of Soil Health generated overall the highest scores, followed by A-CSHSF, and W-CSHSF respectively. Results from BSR analysis revealed that AC was the best single predictor of soil health, and that AC combined with protein, P and pH offered additional predictability, suggesting them for S-CASH. This study highlights a noteworthy advancement towards achieving the first full and simplified SH assessment framework in Colombia.