Soil tests, vouchers, and the limits of site-specific fertilizer recommendations: Experimental evidence from Malawi
Fertilizer subsidy programmes dominate agricultural spending in several African countries. Rising and volatile fertilizer prices have renewed concerns about the efficiency of such spending, prompting initiatives to tailor fertilizer recommendations to local soil conditions. We test this premise in Malawi, where the national subsidy programme distributes a standard package of urea and NPK fertilizer. In a cluster-randomized trial involving more than 2,000 households across 113 villages, we assign farmers to (i) a plot-level soil-test recommendation, (ii) the same recommendation combined with a voucher of subsidy-equivalent value, or (iii) a control group. The recommendation alone has no effect on fertilizer use, input choice, or maize yields. When paired with a voucher, fertilizer use and maize yields increase substantially, with yields rising by roughly one-third; at the maize prices prevailing in our study area, however, the value of this additional production falls short of the face value of the voucher, let alone the value of the voucher plus the cost of individualized soil test. For farmers themselves the package is nonetheless profitable, since the voucher largely displaces fertilizer they would have bought anyway and so lowers their own input spending, and because many households are net maize buyers, valuing the additional output at retail rather than farmgate prices narrows the shortfall. The yield gains do not reflect adoption of site-specific prescriptions: voucher recipients predominantly purchase urea and NPK in proportions closely matching the standard subsidy bundle, regardless of what their soil test recommends, and compliance with recommended alternatives such as potassium, lime, or calcium ammonium nitrate is negligible. Because the observed gains come almost entirely from nitrogen intensification while phosphorus, potassium, and lime gaps remain uncorrected, the measured yield response is a lower bound on what full-compliance fertilization could deliver. Relaxing financial constraints thus increases input use and productivity, but information alone does not redirect behaviour toward precision fertilization. Effective subsidy reform will require addressing broader supply- and demand-side constraints, including input availability, farmer familiarity with recommended products, and the practical implementation of site-specific recommendations, not only improving agronomic information.
Authors
Assefa, Thomas; Atkinson, Jonathan; Ayalew, Hailemariam; De Weerdt, Joachim; Siyame, Edwin W. P.; Spielman, David J.; Van Campenhout, Bjorn
Citation
Assefa, Thomas; Atkinson, Jonathan; Ayalew, Hailemariam; De Weerdt, Joachim; Siyame, Edwin W. P.; et al. 2026. Soil tests, vouchers, and the limits of site-specific fertilizer recommendations: Experimental evidence from Malawi. https://hdl.handle.net/10568/183376
Keywords
Africa; Sub-saharan Africa; Southern Africa; Capacity Building; Inputs; Subsidies; Fertilizers; Soil Analysis; Industrial Supply
Access/Licence
Open Access
