Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) are two forms of mass spectrometry used to measure the presence and quantities of non-nitrogen elements in fertilizer including Ca, Fe, K, Mg, Na, P, and S. The spectrometer converts elements to a gaseous state and then assesses the wavelengths of the light to detect the presence and quantity of elements present in the sample.

# **Agronomic Quality: Evidence**

Assessment of bag characteristics including bag weight and expiration date and of observable fertilizer quality attributes is done based on observation. Bag weight shortages within 1% of the weight reported on the fertilizer label are permitted in international regulatory systems though these can vary by region and country; a 50kg bag missing less than 0.5 kg would be in compliance and those more than 0.5 kg short are out of compliance (OOC). Granular integrity, caking, and presence of impurities and discoloration is often evaluated based on visual assessment. In Michelson et al. (2021) these characteristics were independently coded by two enumerators from photographs of the sampled fertilizers with each characteristic assessed as either present or not. IFDC assesses bag condition and weight of the bag, granule segregation, granule integrity, caking, moisture content by observation and/or feel of the fertilizer and qualitatively and separately rates these characteristics for a given sample as none, low, medium, or high (Sanabria et al. 2013).

Evidence suggests that agronomic quality issues are relatively rare but are (1) more common in multinutrient fertilizers than in single-nutrient fertilizers and (2) are rarely due to adulteration.

Nutrient content shortages in fertilizers tend to be quantified in terms of both the frequency with which they occur in sampling and their severity. Samples are classified as in compliance or out of compliance but also by how much they are out of compliance.

# **Urea**

Evidence on urea fertilizer quality suggests that nitrogen deficiencies in urea are extremely rare. As a single nutrient fertilizer, errors in manufacturing are unlikely; the urea molecule contains 46% nitrogen (N) and reducing that content during manufacturing is difficult and uncommon. Adulteration and counterfeiting in urea are also unlikely given (1) the color, size, and textural uniformity of the urea prills which makes successful adulteration difficult and (2) it is only profitable to dilute fertilizer with something cheaper than the fertilizer itself, and urea is low-cost relative to plausible adulterants (table salt, kaolin). Foreign substances like sand are visually detectable and hard to pass unnoticed.

Table 1 (based on a table in Hoel et al. (2021)) summarizes the results of recent IFDC reports and academic studies based on sampling and testing the nitrogen content of urea fertilizer. All studies are conducted in Sub-Saharan Africa. Nearly all academic studies have focused on urea fertilizer. Studies include samples collected from retail shops, wholesalers, importing ships, and farmers. Quality issues prove rare with the exception of two studies: an analysis of fertilizer quality in Ghana conducted by IFDC in 2010 in which 9% of the samples (21 out of 222) had insufficient nitrogen and a study 12