Developing Standard Protocols for Agricultural Soil Quality Monitoring and Assessment using a Chronosequence in Western Kenya as a Case Study.

Africa’s agricultural viability and food security depend heavily on the quality of its soils. While approaches to measuring air and water quality are widely established, soil quality (SQ) assessment protocols are largely non-existent, especially for use in the tropics. The Cornell Soil Health Test (CSHT), recently developed in New York State for public soil testing, uses a set of inexpensive, agronomically meaningful, low-infrastructure-requiring indicators of SQ. It identifies constraints in agronomically essential soil processes, and differences between management practices, and thus helps farmers target management practices to alleviate quantified constraints. The CSHT may provide a practical framework from which to develop standardized soil quality assessment internationally.

Using a pre-established experiment on 0 to 100+ year old farms at the Kakamega and Nandi Forest Margins in Kenya, we tested SQ indicators that make up the CSHT for their ability to show known trends over time, soil types and management systems, and their potential correlations with yield. On each farm two long-term management systems were sampled in 2007: continuous maize in low-input monoculture, and a kitchen garden, traditionally maintained close to the home, where household organic wastes are added regularly, and diverse fruit and vegetable crops are grown in polyculture. Short-term experimental plots, with several types of organic carbon inputs (Tithonia, manure, charcoal, and sawdust, added at 18 t C over 3 seasons) and equal NPK fertilizer to prevent macro-nutrient deficiencies, were established in all maize systems in 2005, and were also sampled in 2007. Physical indicators (aggregate stability, available water capacity, and field penetration resistance in surface and subsoil), biological indicators (active C and organic matter) and chemical indicators (EC, and the standard commercially available package of pH, P, K, Mg, Ca, Zn, Cu, S) were measured. Preliminary results will be presented.