Diagnostics

iSDA is committed to diagnosing yield and profit limiting constraints. We do this at an individual field level to help farmers prioritise their investments, and at a project level to help aggregators target support services to farmers. Our applications help field officers quantitatively assess a wide range of yield constraints, ranging from plant nutrient deficiencies to soil structural constraints, and offer solutions for overcoming them. The constraints are diagnosed through observable indicators, in some cases with follow-up laboratory analyses. iSDA’s Bayesian approach provides for updating of our models over time based on observed cases and outcomes.

Diagnosing soil constraints has always posed a challenge to agronomists and farmers due in part to the complexity and high cost of soil tests. iSDA has evolved from playing a major role in the Africa Soil Information Service and now produces iSDASoil, a 30m resolution soil properties map of Africa. Soil properties estimated from iSDASoil provide an input to iSDA advisory apps, which combine soil information with multiple sources of other information to provide reasoned advisory.

iSDA has considerable experience with soil spectroscopy as a diagnostic tool, both in the laboratory and in the field. iSDA is a founding member of the Global Soil Spectral Library and Estimation Service (Shepherd et al., 2022) and is currently extending this service to a near infrared scanner suitable for field use with the support of Foodshot Global. We have gained considerable experience in field spectroscopy through an application on ten thousand smallholder coffee farms in Kenya. We also conduct conventional soil testing in certified laboratories on a limited numbers of samples for calibration and validation purposes, and have experience with the use of sensors for nutrient analysis of plant tissues and manures (Towett et al., 2020).

iSDA monitors its impact on changes in behaviour of farmers, extension officers and aggregators, and on farm yields and profits. We do this on a set of sentinel farms, taking detailed observations and measurements on farmers’ practices, soil conditions, plant growth and development, and yield. This includes control farms where no interventions have been applied and user surveys. We feed back this information into improvements of design of iSDA apps.