AbstractMagnesium deficiency is a major constraint for banana and plantain (Musa spp.) production in highly weathered soils. A study was conducted on an Ultisol (Aquic Haplohumult) of the central mountainous region of Puerto Rico to evaluate the effect of several factors on magnesium availability to plantain. Four target levels of soil exchangeable Mg:K ratios: 0.6, 2.0, 4.0 and 8.0; two lime application treatments: no lime, limed to pH 5.5; and two fertilization programs were evaluated in a split-split plot experimental design. Results indicated a highly positive correlation between soil magnesium levels and crop performance. Significant effects were observed on days to flowering, plant height, number of leaves at flowering, leaf magnesium content, and yield. A 25% yield increase was observed at the lowest magnesium increment relative to the control. In addition, the ratio of nonbearing plants per experimental plot was reduced with increments in soil magnesium. It was calculated that in this soil a value close to 2.0 cmol (+)/kg soil would be needed to reach the 0.30% leaf tissue concentration considered critical for bananas and plantains. This value may vary for soils because of different mineralogy, and also because of the influence of factors affecting the availability of magnesium to plants (e.g., antagonistic effect of potassium, magnesium fixation). Our results confirm the need to base fertility recommendations on a soil test. Establishing a universally recommended dosage for all soils of the island, as has been attempted in the past, would be highly impractical because of the highly heterogeneous nature of the soils in Puerto Rico.
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