Pressurized Hot Water Procedures for Use on Small Farms in Developing Countries

Abstract

Soil analysis for small farms in developing countries is often inconvenient and prohibitively expensive, yet the information gained from these soil tests could result in significant benefits. Based on tests done on a limited range of soils, the pressurized hot water (PHW) extraction coupled with colorimetric or turbidimetric analysis is a promising alternative. Before this extraction and analysis can be used in developing countries, testing is needed across the range of soils found in these countries. At Brigham Young University (BYU), 228 soils from Guatemala and Morocco were analyzed for NO₃‐N, phosphorus (P), and potassium (K) using standard methods (water–CTA, Olsen–molybdic acid and ammonium acetate–atomic absorption, respectively). Results were correlated to values obtained from the PHW extraction coupled with colorimetric or turbidimetric analytical procedures. The relationships between these tests were good (r² values of 0.96, 0.71, and 0.52 for NO₃‐N, P, and K, respectively). In an additional study comparing several P extraction methods for Guatemala soils, relationships between PHW‐extractable P and Olsen‐, Bray I–, and Mehlich I–extractable P (r² values of 0.75, 0.67, and 0.46, respectively) suggest that PHW is a promising P‐extraction procedure for use in Guatemala. Overall, PHW extraction and accompanying analyses are a less expensive alternative to current soil nutrient extraction and analysis procedures for the soils of Morocco and Guatemala.

Keywords:

• Bray I
• developing countries
• Mehlich I
• nitrate
• Olsen
• phosphorus
• potassium
• pressurized hot water
• soil extractants