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The Effects of Exchangeable Calcium on the Retention and Fixation of Phosphorus by Clay Fractions of Soil
Author(s) -
Ragland J. L.,
Seay W. A.
Publication year - 1957
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1957.03615995002100030004x
Subject(s) - loam , phosphorus , soil water , saturation (graph theory) , chemistry , calcium , silt , mineralogy , environmental chemistry , soil science , geology , mathematics , paleontology , organic chemistry , combinatorics
Laboratory studies were made of the phosphorus retaining and fixing properties of four Kentucky soils. The soils studied were: Armour, Pembroke, and Memphis silt loams, and Loradale silty clay loam. All work was done with the clay fraction of the soils. The effect of percent calcium saturation of the clay, rate of phosphorus application, and initial saturating cation were studied. Retained phosphorus was considered to be that portion of the added phosphorus removed from a water solution by the clay separate. Fixed phosphorus was considered to be that portion of the retained phosphorus not recovered from the clay separate by extraction with 0.005 N H 2 SO 4 . Radioactive phosphorus was used in the experiment. Phosphorus retention and fixation were determined by a solution counting technique. With a rate of 100 parts of P 2 O 5 per million parts of clay, phosphorus retention and fixation by the four initially acid saturated clay fractions increased as the percent calcium saturation of the clay was increased. No sizeable increase occurred until the clay separates were about 60% calcium saturated. When phosphorus was applied to Loradale clay separate at a rate of 800 or more parts of P 2 O 5 per million parts of clay, fixation decreased with increasing percentages of calcium saturation. This would indicate that fixation studies should be carried out with rates of phosphorus application comparable with those used on field crops if laboratory results are to be extrapolated to field conditions. Initially aluminum saturated clay separate retained much more of the added phosphorus but fixed no more of it than initially acid saturated clay separate. Phosphorus fixation by clay separates with “natural” base saturation decreased with increasing pH, whereas fixation by initially acid saturated clay separate increased or remained unchanged with increasing pH. This may indicate that fixation studies made with initially acid saturated clay separates are not accurate indications of fixation as it occurs under natural soil conditions.