THE EFFECT OF SULFUR AND PHOSPHORUS ON THE AVAILABILITY OF IRON TO PINEAPPLE AND MAIZE PLANTS

Abstract

Pineapple soils with a high annual rainfall are relatively very acid, because they are deficient in such water-soluble bases as K, Ca, and Mg. Pineapples grown in such soils respond very favorably to phosphate fertilizers due to the slight solubility of phosphates, which, under such conditions, form various relatively insoluble compounds with either Fe or Al, releasing water-soluble Fe and P in quantities very small but sufficient for normal development. Pineapple soils with a low annual rainfall have a relatively high pH (6.0-7.0), due to their high content of such bases as K, Ca, and Mg in combination with either strong or very weak acids. They do not respond to high or moderate applications of phosphates on account of their high pH values, at which phosphates in combination with either K, Ca, or Mg are relatively soluble and interfere with the solubility of the small traces of water-soluble Fe which exist under such conditions. If such soils are rendered more acid with S or with acid fertilizers, or are supplied with forms of slowly available Fe, they stimulate plant growth very appreciably even in the presence of moderate applications of phosphates. The solubility of Fe and its availability to plants should be watched in the application of phosphate fertilizers. The biological method of determining Fe deficiency, at least with certain plants, is more sensitive than chemical methods recommended.