Relation of Soil Potassium and Magnesium to Magnesium Nutrition of Citrus

Abstract Soil and leaf analyses were made in connection with six field experiments involving orange trees fertilized with potassium and/or magnesium. Experimental plots were located in 6 orchards in 4 southern California counties. The concentration of magnesium in spring‐cycle leaves was correlated with the degree of leaf symptoms characteristic of magnesium deficiency. Addition of magnesium fertilizer resulted in a marked increase in leaf magnesium and a disappearance of deficiency symptoms. Potassium fertilization accentuated magnesium deficiency. Deficiency symptoms were associated with leaf magnesium concentrations of 0.20% or less. The ratio of exchangeable K/Mg in the soil (particularly the 18‐ to 30‐inch depth) was highly correlated with the percent magnesium in the leaves.