Simplified Soil Analysis Procedure for Use in Small‐Scale Agriculture

Abstract

Soil analysis for small‐scale farms in developing countries is often inconvenient and prohibitively expensive using currently available procedures, yet the information gained from these soil tests could result in economical and environmental benefits. The pressurized hot water (PHW) extraction coupled with colorimetric or turbidimetric analysis shows promise as a viable alternative based on tests done on a limited range of soils. 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 different areas of 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 the values for these tests were good (r² of 0.96, 0.71, and 0.52 for NO₃‐N, P, and K, respectively). Soils from each country were concurrently analyzed for NO₃‐N and P in laboratories in Guatemala and Morocco, and these results were correlated with those from BYU. Positive correlations between BYU values and those from other laboratories were obtained, with the data from the Guatemalan laboratory showing overall closer correlation than the Moroccan laboratory. In an additional study comparing several P extraction methods for Guatemalan soils, relationships between PHW‐extracted P and Olsen‐, Bray I‐, and Mehlich I‐extracted P and measured at BYU (r² of 0.75, 0.67, and 0.46, respectively) indicate that PHW is a promising alternative P extraction for use even with the highly variable soils of Guatemala. Overall, the data support PHW extraction and accompanying analyses as a less expensive alternative to current soil nutrient extraction and analysis procedures for the soils of Morocco and Guatemala.

Keywords:

• Developing countries
• nitrogen
• phosphorus
• potassium
• pressurized hot water
• soil analysis

Acknowledgments

Financial support for this research was contributed by the Benson Food and Agriculture Institute, the Potash and Phosphate Institute, and the Department of Plant and Animal Sciences at BYU. The authors also gratefully acknowledge the technical assistance of Rachidi Hicham and Mohamed Oussible in Morocco, Gadid Artereaga and Fredy Coronado in Guatemala, and Scott Allen, Angela Demeester, Heather Hunsaker, and Amanda Sylvester at BYU.