The behavior of soil-applied cyclotri- and cyclotetraphosphate in Texas soils
Date
1993
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Texas A&M University
Abstract
Cyclotriphosphate (C3P) is of interest to soil scientists because it demonstrates little or no retention by soil constituents. Non-sorption is desirable in the development of mobile P fertilizers. Work was expanded to include cyclotetraphosphate (C4P), a larger but commercially unavailable cyclic P compound that is more stable than C3P in solution. High-purity C4P was prepared by ethanol precipitation of the hydrolysis products Of P4010. Improved methods of ion chromatography were applied to the analysis of cyclic P and all hydrolysis products extracted from soil using a water/0-5 M H2SO4/1 .0 M NAOH extraction procedure developed for this work. Separation and direct quantitative analysis of linear and cyclic polyphosphates were accomplished in less than 15 minutes. The rapidity and ease of these analyses represent a vast improvement over previous methods of polyphosphate analysis. Four diverse Texas soils received 1 00 and 400 gg cyclic P g-1 soil as either C3P or C4P and were incubated under different water, temperature, biological activity, and time regimes. The larger C4P was not appreciably sorbed in soil and was more stable than C3P under all conditions. Rate constants and the time to one half of initial P concentration were determined for each P. Kinetic data suggested that the hydrolysis of cyclic P in soils is complex, but cyclic P hydrolysis most likely follows first-order kinetics. The mechanism of C4P hydrolysis- particularly at low P application rates-may involve direct conversion of C4P to diphosphate and triphosphate (in addition to tetraphosphate), possibly due to phosphatase action in C4P hydrolysis. Temperature dependency of C3P and C4P hydrolysis was examined. All treatments showed Qlo < 2.0, indicating the prominence of biological hydrolysis in cyclic P decomposition in soils. Energy of activation (EA) was 45.8 and 61.1 kJ mol-1, respectively, for C3P and C4P on Falba sandy loam at the low P rate (38.6 and 51.2 kJ mol-I for the same treatments on Branyon clay). Nineteen soil parameters were examined for correlation with C3P and C4P hydrolysis. Numerous significant correlations (P < 0.05) were reported, but high intercorrelation among related soil factors was suspected, thus reducing the value of correlation analysis.
Description
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Includes bibliographical references.
Includes bibliographical references.
Keywords
soil science., Major soil science.