Response of 'Cadoux' clementine to foliar potassium fertilization: effects on fruit production and quality
2015
Hamza, Abdelhak | Bamouh, Ahmed | El Guilli, Mohammed | Bouabid, Rachid
‘Cadoux’ clementine is a citrus fruit well appreciated by consumers. However, this cultivar produces fruits of small to medium size that are fairly accepted commercially. In a field study, we evaluated the effects of rates and frequencies of foliar potassium (K) fertilization, applied either as potassium nitrate (KNO3) or potassium sulfate (K2SO4), on fruit production (fruit size, weight and yield) and quality parameters (skin thickness, firmness, color index, maturity index, juice content, acidity and total soluble sugars). Concentrations of foliar fertilizer solutions were 5 and 8% (m/v) for KNO3, and 2.5 and 4% (m/v) for K2SO4, applied either two or three times during fruit growth on orchards with three planting densities (D1: 6×6 m, D2: 5×6 m and D3: 6×3.5 m tree spacing). In all treatments, after potassium sprays, K (% DM) content increased in the leaves of clementine ‘Cadoux’ between 12 and 40% compared to their initial K levels while in the control this content dropped about 15% compared to its initial content (before K sprays). Fruit weight increased with K application rate and frequency. K fertilization treatments in three foliar applications showed the best percentages of fruits of extra size class, whatever the source of K (KNO3 or K2SO4) or plant density. Foliar applications of K also increased fruit color, firmness and rind thickness. Fruit juice content, acidity and total soluble solids slightly increased with foliar K application. Raising K concentration and the number of foliar applications increased tree fruit production. In terms of efficiency of foliar K fertilizers, 4% K2SO4 in three applications resulted in maximum gain of fruits per kg of foliar fertilizer.
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