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Effect of lime on the dissolution of two phosphate rocks in acid soils
Author(s) -
Hanafi Mohamed M.,
Keith Syers J.,
Bolan Nanthi S.
Publication year - 1992
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740600204
Subject(s) - dissolution , chemistry , soil water , sink (geography) , lime , calcium , incubation , leaching (pedology) , calcium carbonate , phosphate , carbonate , environmental chemistry , mineralogy , inorganic chemistry , soil science , geology , biochemistry , paleontology , cartography , organic chemistry , geography
The effect of pH and calcium (Ca) on the dissolution of Gafsa (GPR) and Christmas Island A (CIPR) phosphate rocks (PR) was examined in closedincubation and open‐leaching systems in six acid, Malaysian soils. The pH of the soils was increased to between 4.5 and 6.1 by incubating with calcium carbonate (CaCO 3 ); soil was also incubated with calcium chloride (CaCl 2 ) to provide equivalent amounts of Ca without causing any marked change in pH. In the closed‐incubation system, dissolution of reactive GPR was overall higher (11–70%) than for the less reactive CIPR (12–43%) after 60 days of incubation. Dissolution of PR decreased with increasing levels of CaCO 3 or CaCl 2 , but the decrease was more pronounced in CaCO 3 ‐treated than in CaCl 2 ‐treated soils. Increasing additions of CaCl 2 decreased the size of the available sink for Ca from 84.0 to 0 mmol (+) kg –1 soil. Although the addition of CaCO 3 increased the cation‐exchange capacity (CEC) of these variable‐charge soils (from 23.0 to 199.0 mmol (+) kg –1 soil), most of the newly‐created exchange sites were occupied by Ca added through CaCO 3 . This was responsible for the decrease in size of the sink for Ca. Addition of CaCO 3 also decreased the proton supply from 260.7 to 0 mmol (+) kg –1 soil, which in conjunction with the decrease in size of the Ca sink decreased the dissolution of PR. The effect of CaCO 3 and CaCl 2 on PR dissolution varied between soils and was related to pH‐buffering and the Ca‐sink size. In an open‐leaching system, large amounts of Ca (8–40%) added as CaCO 3 were removed in the leachate and hence the decrease in GPR dissolution with CaCO 3 addition was less in the open‐leaching than in the closed‐incubation system.