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.
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McColloch et al. (1957) studied this question.