Recently, research has focused on the relationship of poor or uncertain agricultural input quality to input use (Michelson et al. 2021, Ashour et al. 2019, Bold et al. 2017). Substandard quality, whether actual or merely suspected, could partially explain limited deployment of needed inputs, and consequently crop response and profitability. Accurate measurement of the quality and quantity of agricultural inputs applied by farmers is therefore essential for two purposes: raising farmer confidence about investing in such inputs, and improving farm yields through use of those inputs.

This paper reviews the evidence regarding the quality of mineral fertilizer and pesticides, inclusive of herbicides, available in local markets in Sub-Saharan Africa.<sup>3</sup> We review current evidence from academic studies and published reports by expert agencies including the International Fertilizer Development Center. We discuss best practices for definition and measurement of quality. We also summarize research eliciting and evaluating farmer assessment of fertilizer and pesticide quality. Our contribution is to introduce important distinctions based on the body of extant research into the academic literature on the topic of input quality and to identify important evidentiary gaps and areas for future research.

Our review of available evidence produces four primary findings. First, we show that current research on fertilizer and pesticide quality has focused primarily on two inputs: urea fertilizer and glyphosate herbicide. These are widely used agricultural inputs – especially by smallholder farmers – and both are critical for agricultural production. However, insights related to these inputs are not necessarily relevant to other fertilizers and pesticides, which make up a large share of input use.<sup>4</sup> Our second finding is relevant to this point: available evidence strongly suggests that quality problems vary by input. For example, though nutrient quality problems are exceedingly rare in urea fertilizer, nutrient shortages are more common and more likely in fertilizer blends including nitrogen, phosphorous, and potassium (NPK), calcium ammonium nitrate (CAN), and diammonium phosphate (DAP) and in glyphosate herbicide. The magnitude of the problem also varies by input: while evidence suggests nutrient shortages tend to be relatively modest in the fertilizer blends, economically and agronomically significant problems have been found in packaged glyphosate in the region.

Third, input quality issues have different causes. While the largely modest nutrient shortages in fertilizer blends are likely attributable to problems with manufacturing and storage, problems in herbicide could be due to faulty manufacturing, counterfeiting, or adulteration. Glyphosate quality issues also exhibit considerable spatial variation. Research designed to understand and ultimately

> 3 We do not review the evidence on hybrid seed quality, which is still emerging. Measuring seed quality involves assessing three dimensions: analytical purity, germination rates, and varietal purity. Work studying hybrid seeds and farmer beliefs about hybrid seed fidelity includes Gharib et al. (2021) and Barriga and Fiala (2020), with related work on misperception and misreporting of crop variety by Wossen et al. (2022).

> 4 For example, data from Malawi’s Fifth Integrated Household Survey (2019/20) suggests that ~18% of cultivating households applied urea to at least one plot, while ~53% applied a different type of mineral fertilizer to at least one plot (rainy season; authors’ calculation). Similarly, data from Nigeria’s General Household Survey Panel (2018/19) suggests 24% of households applied urea on at least one plot, and 34% applied an alternative mineral fertilizer (authors’ calculation).

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