Relationship between soil and leaf mineral nutrient concentration and yield of selected citrus species

Abstract: Low yields of citrus in Trinidad prompted an investigation to determine whether infield yield variation in citrus was due to differences in plant nutrition induced by field variability. Selected trees of three cultivars (Valencia orange (Citrus sinensis), Portugal mandarin (C. reticulata) and Ortanique tangor (C. sinensis x reticulata) were monitored for one to two years and indicators of yield such as percent fruit set, fruit count and fruit quality measured. Leaf nutrient content of the trees and nutritive factors of the soil in the root zone were also determined. Nutrient deficiencies were found in the fields of all the three cultivars. The most common deficiencies were of calcium, zinc and magnesium. There was limited evidence of yield correlation with soil pH (P = 0.012), and leaf phosphorus content (P = 0.02), Zn (P = 0.005) and N (P = 0.001). DRIS analysis supported the notion that infield yield variability was associated with nutrients that were limiting. Percent fruit set was associated with Ca/Mg ratio (r = 0.542, P = 0.045; r = 0.607, P = 0.016) and foliar concentration of micro elements Cu (r = 0.738, P = 0.003; r = 0.667, P = 0.007) and Fe (r = 0.507, P = 0.064; r = 0.573, P = 0.026) in 1997 for one field each of Valencia orange and Portugal mandarin, respectively. The most commonly derived relationship for fruit quality was a negative relationship of leaf nitrogen concentration with fruit weight. A positive relationship between leaf concentration of manganese and peel thickness occurred in Portugal mandarin for the two years of the study.