Critical Levels of Soil‐ and Nutrient‐Solution Calcium for Vegetative Growth and Fruit Development of Florunner Peanuts

The separate effects of rooting‐ and fruiting‐zone Ca upon vegetative growth and fruit yield of ‘Florunner’ peanuts ( Arachis hypogaea L.) were investigated in nutrient‐solution experiments where rooting and fruiting media were segregated. At low levels of rooting‐zone Ca, both vegetative and fruit growth were influenced by rooting‐ and fruiting‐zone Ca acting in concert. As root zone Ca was increased above the “critical” level for maximum vegetative growth, the plant changed from being almost fruitless to a well‐fruited plant. Results of nutrient‐solution studies in the growth chamber were verified in a greenhouse soil experiment using surface soil of a Dothan loamy sand (Plinthic Paleudult). Composite results from soil and nutrient‐solution experiments identified three separate “critical” solution Ca levels. Expressed as the activity ratio of Ca/total‐cations, the levels were: 0.10 for vegetative growth, 0.15 for flower fertility or fruit load, and 0.25 for pod fill. Substituting K for Mg in solution caused a lowering of the “critical” Ca levels.