Lime, Gypsum, and Basaltic Dust Effects on the Calcium Nutrition and Fruit Quality of Pineapple

Pineapples grown in acid soils containing high levels of manganese (Mn) can exhibit iron deficiency because Mn interferes with iron bio-functioning. This situation is commonly corrected with regular iron sprays. Soil Mn concentration can be reduced by liming, but pineapple growers keep the soil pH below 5.0 because it helps reduce the incidence of rots caused by Phytophthora sp. This study was conducted in Hawaii on an acid soil high in Mn to evaluate the effects of calcium source (lime, gypsum, and basaltic dust, a quarry by-product), on soil pH, plant iron utilization, and plant calcium nutrition of a low-acid hybrid pineapple. The effects of calcium source and amount on fruit translucency, acidity and sugars were also examined. Without iron sprays, no calcium source prevented severe iron deficiency in this acid soil. When pineapple was sprayed with iron, all calcium sources increased calcium levels in the soil and in D-leaf and fruit tissues. Basal-white leaf calcium in the treatments ranged from 0.19 to 0.55% and all levels were at or above those considered adequate; green tissue levels ranged from 0.11 to 0.20%. There were no significant effects of treatments on plant growth, fruit weight, fruit size distribution or most indices of fruit quality. Further analysis showed that the fruit translucency index (TI) decreased as the amount of calcium applied was increased and 64% of the decrease in TI was accounted for by applied calcium. There was also a significant negative correlation between TI and extractable soil calcium, basal white and green D-leaf calcium, and fruit calcium. Lime can raise soil pH to levels that can increase the incidence of root and heart rot while gypsum and basaltic dust will supply calcium without increasing soil pH. Basaltic dust could provide calcium as well as other nutrients in organic farming. INTRODUCTION: Pineapples are well adapted to acid soils and tolerate relatively high levels of soluble aluminum and manganese. In soils containing large amounts of soluble iron and manganese, pineapple plants can absorb relatively large amounts of both elements but apparently are unable to effectively utilize absorbed iron, resulting in severe iron deficiency. Manganeseinduced iron deficiency in pineapple is corrected by regular sprays of iron, usually as iron sulphate. Soils with low pH=s also tend to have low concentrations of soil calcium and liming such soils increases soil pH, soil calcium supply, and reduces soluble levels of manganese and aluminum. However, pineapple growers are cautioned to lime carefully because the incidence of root rot problems caused by Phythopthora sp. increases as pH rises (Swete Kelly, 1993), and the problem is more severe above pH 5.5 (Frossard, 1976). Low soil calcium can induce calcium deficiency symptoms in the plant and fruit (Malezieux and Bartholomew, 2003 ), but calcium levels above those found to be sufficient for normal plant and fruit development can still provide benefits. Liming raises soil pH and