Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Studies were conducted on apparent phosphorus fixation in 54 soils of Louisiana to determine the effects of different rates of P application on the recovery of P, and to develop appropriate regression model for predicting extractable P and recovery of P by using 4 extractants. Soil samples were equilibrated with aqueous solution of P for 7 days, and were then extracted with the 4 solutions. With the exception of the soils of the Mississippi River area, Bray II solution removed significantly larger quantities of P than did the 3 other extractants. Phosphorus removed from soils with the extractants showed wide differences. Extractable P increased with increasing rates of P application. Recovery of P also showed linear relationships in most soils. Only in few soils, the recovery of applied P showed curvilinear relationships. Application of P at rates of 40, 60 and 80 mg kg('-1) gave higher recoveries than did the other rates of P. The 4 solutions were almost equally reliable in extracting P from soils. Regression equations were developed for predicting extractable P and recovery of P with 4 extractants. Investigations were conducted to determine P sorption/desorption characteristics of ten soils of Louisiana. Fifteen gram soils samples were incubated at 25(DEGREES)C with 150 ml of 0.005 M Ca(NO(,3))(,2) solution containing P from 20-200 mg kg('-1) as Ca H(,2)(PO(,4))(,2) (.) H(,2)O for 1-14 days. Quantities of P sorbed and in solution at various incubation times from different rates of P application were determined. Linear regression equations were developed for predicting solution P at 1-14 days following application of P. Time dependence of P were shown by plotting log of solution P vs. time and log of soil P vs. extraction times for sorption and desorption studies respectively. Isotherms were constructed by plotting log of sorbed P against log of solution P at various times for both sorption and desorption studies. Linear regression equations were developed for predicting sorbed P for various levels of solution P in soils. Solubility of P was greater when P was added to soils than when P was desorbed.

Pages

210

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