Onions require potassium at rates equal to nitrogen, but calcium is required at considerably higher rates. High nutrient availability is important during bulb-formation; in this phase a high K:N ratio is required. Pungency of flavor is enhanced by fertilizers containing S but diminished by N in ammonium form. Root system is shallow and fibrous, therefore, fertilizers should be applied 10–15 cm below the seed row. Optimum soil pH >6.0. Best onion mineral nutrition regime includes the use of CRFs and foliar feeding. In certain areas fertigation with fully-soluble fertilizers is also practiced.