Haggblade et al. (2021) find a strong relationship between bad formulation and a brand being unregistered in their study. They find no relationship between price and the accuracy of the stated concentration, nor do they find that older products (based on the labeled date) are more likely to have quality problems.

# **VI. Farmer Beliefs**

For both fertilizers and for pesticides, it can be difficult for farmers to evaluate quality. The quality signal may be somewhat easier for farmers to detect with pesticides as evaluating the effectiveness eliminating a weed is likely more direct and immediate than fertilizer’s effect on plant growth and yields, however problems related to pesticide suitability and application technique can obfuscate and obstruct learning. Non-labor agricultural inputs are experience goods but the weather-driven stochasticity in agricultural production and lack of knowledge about proper use can make them effectively credence goods whose quality cannot be evaluated even after use. Farmers may not be able to assess for days or weeks after application whether the applied input “worked”. They need to see if the plant grew, if the leaves developed discoloration characteristic of unaddressed nutrient shortages, whether the weeds or the insects died. But other factors can also contribute to the effectiveness of these inputs: whether the farmer uses the right input or formulation given particular pest pressures, soil quality, or growing conditions; the timing and amount of rainfall; the timing of application and whether the input was correctly applied. Bold et al. (2017) and Hoel et al. (2021) demonstrate through modeling and simulations the difficulties that these factors present for farmer learning about the quality and effectiveness of the inputs they purchase and apply.

# **Farmer beliefs about fertilizer quality**

Evidence suggests that small farmers have concerns about fertilizer nutrient content and that those concerns may negatively affect their purchasing. Sanabria et al. (2013) indicate in a study of fertilizer in West Africa that farmers report beliefs that adulterated urea is widespread in their markets but that this suspicion lacks scientific support (p. 39). A possible contributing factor: many small farmers purchase fertilizer in quantities less than the 50 or 25kg bags available from manufacturers. Small farmers purchase one or two kilograms at a time from open bags in agri-dealer shops or in small plastic bags that are repacked for sale from opened bags by agri-dealers. This practice of selling fertilizer from open or repacked bags is a source of considerable suspicion regarding fertilizer quality in many markets, both among farmers and among fertilizer regulators. In several countries the practice of purchasing from open bags is illegal but still a primary means by which small farmers acquire fertilizers.

Five studies (Bold et al. 2017, Ashour et al. 2019a, Hoel et al. 2021, Maertens et al. 2021, and Asante et al. 2021) have directly elicited farmer beliefs about mineral fertilizer quality. Consistent with other academic studies on fertilizer quality in low-income countries, these elicitations have focused on urea. These studies all find that farmers on average believe that there are quality problems in urea in their local markets, despite evidence to the contrary.

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