The reactions of trimetaphosphate (TMP), tripolyphosphate (TPP), pyrophosphate (PP), and orthophosphate (OP) with an Elliot soil were studied.
The hydrolysis reaction TMP→TPP→PP + OP→3 OP was studied by equilibrating TMP added to the Elliot soil at a rate of 400 µg. P/g soil and measuring TMP, TPP, PP, and OP at various times. These measurements showed that TMP persisted less than 1 day and TPP less than 8 days. Less than 10% of the PP formed had been hydrolyzed after 16 days.
The sorption of TMP, TPP, PP, and OP in the soil was studied. TMP was not appreciably adsorbed by the Elliot soil. The P adsorption capacities for OP, PP, and TPP calculated from the Langmuir equation were 462, 965, and 706 µg P/g soil, respectively.
A method for extracting and determining TMP, TPP, PP, and OP in soils was developed. The method consisted of two extractions (2% EDTA + 0.1N NH4F pH 4.2 and 2% EDTA + 1N NAOH), followed by an anion exchange resin separation of the P forms. Recovery of added P was 94% using these extractants. The average error for the extraction and separation was 17%.
Plant uptake of P from soil treated with PP was slightly higher than soil treated with OP.