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, magnesium nitrate and ammonium nitrate, as per the above-mentioned phase-specific rates.
Recommended N-P-K-Ca-Mg ratios, applied by fertigation via drip irrigation, across main growth stages of cv. Arbequina (for oil extraction) olive trees, at Mediterranean (Tunisia) conditions, with an expected yield of 13.2 MT/ha. Ref. Ben Khelil & Mustafa, 2013; El Fouly, 2014, and others.