Abstract

Pummelo-growing soils in southern Thailand are usually low concentrations of potassium, calcium, magnesium and zinc; therefore, the roles of these elements are essential and their effects on nutrient uptake and fruit quality that should be considered in this area in current and future pummelo orchard. The study was carried out during 2013 to 2014 production year on a 17 year pummelo (Citrus maxima Merr.). The objective of the study was to examine the effects of ammonium (NH₄), potassium (K), magnesium (Mg) and zinc (Zn) fertilization over the farmer practice on nutrient uptake and fruit quality. The experiment comprised of 5 treatments; apply all, not apply NH₄, not apply K, not apply Mg and farmer practice. Application of fertilizer increased N, Ca and Mg concentrations in the leaves, but K and Zn concentrations in leaves decreased after application. However, their concentrations were in optimum ranges. High K/Ca, K/Mg mole ratios and low exchangeable Mg in soil positively affected on K uptake. Low Ca/Mg mole ratio and low exchangeable Ca in soil negatively affected on Ca uptake. The TSS and TSS/TA tended to decline when the treatments were not applied K-fertilizer. The fruit qualities were greater in the treatments with K/Ca, K/Mg and Ca/Mg mole ratios in soil were 0.23 to 0.27, 0.63 to 0.71 and 2.35 to 3.08, respectively. This study showed that K and Zn still required for pummelo growing in this soil.

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