The following plan is suggested for realizing the said requirements, for field onions with a life span of 120 days, and an expected yield of 45 MT/ha, by fertigation via drip irrigation.
Potassium nitrate should be used as the primary source of potassium, and a partial source of nitrogen. The balance of nitrogen should be sourced from calcium nitrate, and ammonium nitrate, as per the following phase-specific rates. Trace nutrients should be applied as per soil-, and leaf analysis.
This plan presents the mineral nutrition scheme, in terms of the mass proportions between all macro-, and secondary- nutrients.