ABSTRACT: Pummelo growing soil in Khanom District, Nakhon Si Thammarat Province is strongly acid.
Phosphorus, potassium, calcium, magnesium and zinc are lower than sufficient amounts according to a standard
recommendation of our previous study. Pummelo shows deficiency symptoms of these nutrients, and farmers have
to apply a large amount of fertilizers to correct these problems. This study was carried out in order to examine effects
of ammonium (NH4
), potassium (K), magnesium (Mg) and zinc (Zn) fertilization over 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 (not apply Zn). Pummelo tended to respond to NH4
manipulation only leaf-N was lower
than 27 g/kg. Concentrations of K and Mg in leaves were in optimum ranges (15 - 20 and 3 - 5 g/kg, respectively),
therefore no any leaf response was found. Concentrations of leaf-Ca were lower than an optimum range (30 - 40
g/kg) in every treatment; therefore pummelo tended to uptake more Ca. Fruit weight, juice volume and test index
(total soluble solid/titratable acidity) tended to decline on the not apply K treatment. This study showed that K is
still required for pummelo growing on this soil, although its concentrations in soil and leaves were in the optimum
range and no K response in leaves.
Keywords: pummelo, plant nutrition, nutrient uptake, fruit quality