The Bouyoucos method in Peruvian soil laboratories: establishing a correction factor to standardize for international methods

Vásquez-Regalado J.; Quispe-Poma M.; Mestanza C.J. · Archives of Agronomy and Soil Science (2026) · DOI: 10.1080/03650340.2025.2598979

Resumen

Soil particle size distribution is a key indicator of physical and chemical properties. While sedimentation is a standard method, its extensive pretreatments and long measurement times have led Peruvian commercial laboratories to adopt modified Bouyoucos methods. The main source of error in these methods is the application of Stokes’ law to laminar flows. This study compared a locally adapted Bouyoucos method (following Peruvian regulations) with the international pipette method using 200 soil samples from La Molina National Agrarian University. Samples, selected to minimize issues with salts, organic matter and calcium carbonate, represented various USDA textural classes. Data were analyzed using the paired Wilcoxon test, and correction factors were developed with regression models. The locally adapted Bouyoucos method overestimated sand and clay (by up to 200 g kg−1) and underestimated silt content (±400 g kg-1). Simple linear regression best predicted sand (R2 = 0.97; RMSE = 41.34 g kg−1), while multiple linear regression optimized clay (R2 = 0.94; RMSE = 52.65 g kg−1). These discrepancies altered 41% of the textural classes. The proposed correction factors, 0.9511 for sand and 0.975 for clay, will standardize Peruvian soil data with global standards.

Instituciones: Universidad Nacional Agraria La Molina