Grounds for comparison: linking Arabica cup scores to soil fertility and plant nutrition in rust-resistant cultivars and traditional American coffees

Abstract The cup quality of rust-resistant Arabica ( Coffea arabica L.) × Robusta ( C. canephora Pierre ex Froehner) cultivars is thought to be inferior to traditional Arabicas, but few studies have examined the extent to which coffee cup scores are affected by local variation in soil fertility and plant nutrition. We evaluated coffee cup quality using the Specialty Coffee Association’s 100-point Q-grading system and characterized the timing and formulation of soil and foliar nutrient additions across 23 fields in south-central Guatemala managed by smallholder farmers, then compared relationships between soil extractable and total leaf and green bean nutrient concentrations and coffee cup scores for traditional versus rust-resistant Arabica cultivars. All cultivars had similar coffee cup qualities and obtained final cup scores suitable for special coffee market access (> 80.0 points). The timing of nutrient additions closely aligned with local weather conditions, but formulations of foliar nutrient additions differed markedly between cultivars. In > 80% of fields, soil inorganic N, K, Mg and B and leaf S, Zn, Cu, and B concentrations were below minimum thresholds generally ideal for crop production. Despite potential nutrient deficiencies, most cup qualities were positively correlated with leaf Zn for traditional cultivars (R 2 adj = 0.23–0.82) and soil K for rust-resistant cultivars (R 2 adj = 0.34–0.78). Our study demonstrates rust-resistant Arabicas grown in this region of Guatemala can have similarly appealing coffee cup flavor profiles and organoleptic qualities as Bourbon and Typica lineages. However, a larger network of sites is needed to establish reliable soil and/or foliar indicators of coffee cup quality across variable management practices and soil conditions.