Abstract
Fruit yield and quality of citrus trees (Citrus spp.) is markedly affected by potassium (K) fertilization. Potassium chloride is the major source of K, even though other sources are also available for agricultural use when crops are sensitive to chloride or where potential for accumulation of salts in soils exists. Only few studies addressed the effect of K sources on yield and quality of citrus fruits. Therefore, the present study was conducted to evaluate K2SO4 and KCl fertilizer sources at 0, 100, 200, and 300 kg ha-1 per year K2O on fruit yield and quality of 'Pêra' and 'Valencia' sweet orange trees in the field. The experiments were carried out in a 4 × 2 factorial design under randomized complete blocks, with four replicates from 2001 to 2004. Fruit yield increased with increased K fertilization. Nutrient rate for maximum economic yield of 'Pêra' was 200 kg ha-1 of K2O and for 'Valencia', 270 kg ha-1 of K2O. Differences were attributed to higher production and K exportation by fruits of 'Valencia'. Fruit mass also increased with increased K fertilization what decreased total soluble solids in juice, and which correlated with leaf K concentrations for 'Valencia' (r = 0.76; p < 0.05). Leaf Ca, Mg and B concentrations decreased with K rates. Additionally, leaf Cl increased up to 440 mg kg-1 with KCl rates, even though no negative effects occurred either on fruit yield or quality of trees.
Highlights
Fertilizers are required to support adequate mineral nutrition of citrus and to ensure high crop productivity in low fertility tropical soils
Potassium chloride is the major source of K, even though other sources such as potassium sulfate and potassium nitrate are available for agricultural use
A more marked response on fruit yield occurred in Matão, with ‘Valencia’, where the average orange production increased after four harvest seasons from 35 to 50 t ha–1 per year 0 to 300 kg ha–1
Summary
Fertilizers are required to support adequate mineral nutrition of citrus and to ensure high crop productivity in low fertility tropical soils. Fruit yield and quality of citrus trees depends largely on nitrogen (N) and potassium (K) fertilization (Cantarella et al, 2003; Alva et al, 2006), elements which represent the greatest quantity of nutrients exported through harvest (Bataglia et al, 1977; Mattos Jr. et al, 2003). Potassium chloride is the major source of K, even though other sources such as potassium sulfate and potassium nitrate are available for agricultural use. These later are usually more expensive but are preferred for crops that are sensitive to chloride, as citrus (Bañuls and Primo-Millo, 1992), or for those grown where potential for accumulation of salts in soils exists (Laegreid et al, 1999); other characteristics may favor the use of the same via fertigation
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