The fertilizer dosages recommended by Fertilab were divided into two packages according to the timing of application: the first package to be applied at sowing, and the second 30 to 35 days after sowing depending on plant growth. Fertilab also recommended the use of a precision sowing drill at planting to ensure optimal fertilizer use at sowing as well as optimal plant spacing. Finally, the recommendations included the use of pre-emergent herbicides 2 to 40 days after sowing to reduce weeds that could compete for nutrients with the maize plants.

Based on focus group discussions, the research team used the information provided by Fertilab to design a report for farmers that was intuitive and easy to read. The report contained information on (a) plot physical characteristics and nutrient levels, (b) the recommended dosages of nutrients required to achieve a maize yield of 4.5 mt/ha under normal weather conditions, (c) recommended fertilizer amounts and their costs at our partner agro-dealer and (d) a comparison between the farmer’s own 2014 fertilizer costs the costs of the recommendations. The research team was careful to explain the assumptions underlying the recommendations. More details are available in Online Appendix B.

**Specificity of recommendations:** Given the potential heterogeneity in fertilizer recommendations within and across clusters, farmers in _T_ 1 received individualized recommendations, based on the soil analysis from their registered subplot. The rest of the treated farmers in _T_ 2 _− T_ 4 received recommendations based on averages of the soil analyses in their cluster. This averaging was expressly conveyed to them in the report as well as verbally when describing the recommendations. Control farmers received the average recommendations in February 2016, after the intervention had ended.

We assess the heterogeneity in input recommendations by running a standard analysis of variance (ANOVA) in Appendix Table A1. In particular, for registered subplot _i_ in cluster _c_ : _Yic_ = _μ_ + _αc_ + _εic_ and we report estimates of variation within ( _σε_ ) and across clusters ( _σα_ ) and the share of the total variation arising from between cluster variation _σα_<sup>2</sup> _σ_ + _<u>α</u>_<sup>2</sup> _σε_<sup>2.We find substantial</sup> variation in the soil characteristics (panel A) and nutrient recommendations (panel B) both within and across clusters although most of the variation appears to be within clusters.

These results are consistent with Figure 2 which displays the level of N, P and K in the registered plots for the four different agro-climatic areas of the study along with the target level of nutrients required to achieve 4.5 mt/ha according to the Fertilab model. The figure shows that even across different agro-climatic zones, the variation in nutrient content within each zone is much higher than across zones. In addition, Panel (a) of Figure 2 shows a deficit of N relative to the target level of N (red line) which is unsurprising because N is either absorbed by the plant, is lost to the atmosphere or lost via leaching or de-nitrification. Since soil analyses were taken right before sowing for the 2015 season, the N content in the soil should be relatively low. Panel (b) shows a soil level of P that is close to the target level and even higher in some plots, and therefore the recommendations call for relatively low amounts of the P rich fertilizer DAP.

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