2000; Hall et al., 1992). A prominent example of these efforts is the Global Agro-Ecological Zones (GAEZ) initiative, which makes available global geospatial datasets on crop suitability and attainable yield for 53 crops but at approximately 9-kilometer spatial resolution.<sup>3</sup> While the GAEZ data may be useful for assessing crop suitability across expansive geographies, the coarse resolution of this geospatial product limits its use for farm- or plot-level analyses of agricultural productivity in Sub-Saharan African contexts.

Against this background, our paper leverages unique household survey data collected in Uganda, inclusive of plot-level, objective measures of maize yields and soil attributes, to fill knowledge gaps regarding the linkages between soil fertility and smallholder agricultural productivity – both on the whole and within different farmer subpopulations that are defined by socioeconomic characteristics. In doing so, we additionally provide operational insights regarding the integration of objective soil testing into large-scale household surveys, and present empirical evidence regarding the shortcomings of existing geospatial data on soil attributes vis-à-vis plot-level soil sampling and analysis. The data originate from a methodological survey experiment conducted in Eastern Uganda; the top maize-producing region in Uganda where maize is a primary staple crop.

Specifically, our analysis (i) estimates the maize-specific soil suitability profile of each maize plot based plot-level measures of soil attributes and assigns each plot to one of four suitability classes that are anchored in the GAEZ definitions, (ii) demonstrates the heterogeneity, across the soil suitability classes, in observed versus potential levels of productivity – through the estimation of stochastic frontier functions of crop cutting-based maize yields; (iii) quantifies production and income gains from closing suitability class-specific productivity gaps – for the sample as a whole and for various farmer sub-populations; and (iv) documents whether the use of 250-meter resolution AFSIS geospatial data on soil attributes changes our conclusions regarding the relationships between soil fertility and maize yields.

Measuring agricultural productivity on plots of varying levels of maize-specific soil suitability, and the potential gains in productivity on those plots, allows for a more thorough understanding of the ability of agriculture alone to generate significant income gains. And while some existing work integrates ground-based measures of realized crop production, the current literature fails to adequately address the linkages between soil suitability, observed versus potential crop yields, and other household- and community-level factors influencing productivity outcomes.<sup>4</sup> The results indicate that despite the standing of the Eastern Region as Uganda’s leading maize producing region, only 13 percent of farmers are cultivating soil that is highly suitable for maize production, while the vast majority are cultivating only moderately suitable lands. The key soil

> 3 For more information, please visit: https://gaez.fao.org/pages/theme-details-theme-4.

> 4 One notable exception is the work of Jain et al. (2020) who employ a holistic model of soil suitability in India, including socio-economic factors.

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