Protocol for Agricultural Soil Quality Monitoring and Assessment Applied to a Chronosequence with Short- and Long-Term Management Systems in Western Kenya.

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), developed for public soil testing, uses a set of inexpensive, agronomically meaningful, low-infrastructure-requiring indicators of SQ. We tested CSHT indicators for their ability to show known degradation trends over time and differences between management systems. We used a chronosequence including primary forest and 5-80 year old farms at the Kakamega and Nandi Forest Margins in Western Kenya.

 

On each farm short- and long-term management systems were sampled: 1) kitchen-garden management, 2) continuous maize in low-input monoculture (control), and 3) short-term organic matter (OM) additions to maize. Physical (aggregate stability, available water capacity, and penetration resistance in surface and subsoil), biological (permanganate oxidizable “active” C and OM) and chemical indicators (EC, and a commercially available nutrient package) were measured. Scoring curves were developed for all CSHT indicators to interpret whether values showed soil functional constraints. An overall Soil Quality Score was calculated.

 

Exponential decay and other regressions fit to each indicator showed degradation over time for most indicators. A Hotelling T² test showed that kitchen-garden-SQ differed significantly from all other treatments, that controls differed significantly from all short-term OM management systems, and that several of the OM treatments differed from each other. Soil quality was much higher in kitchen-gardens than under continuous maize, and was also higher after short-term OM additions.

 We conclude that the CSHT is useful for monitoring degradation or aggradation over time, for assessing management impacts on soil constraints, and thus for making management decisions. The CSHT may provide a practical framework from which to develop standardized soil quality assessment internationally.