Pyrophosphate Hydrolysis of Ammonium, Calcium, and Calcium Ammonium Pyrophosphates in Selected Texas Soils

Abstract

AbstractFive soils of varying chemical and mineralogical composition were treated with several pyrophosphates, and the rate of pyrophosphate hydrolysis determined. Pyrophosphate hydrolysis was a function of the pyrophosphate compound, soil type, and CaCO3 treatment.Except for Ca2P2O7, hydrolysis rate could not be predicted by the relative solubility of the pyrophosphate compound. For example, in the three acid soils, hydrolysis rates were: CaH2P2O7 = Ca3(NH4)2(P2O7)2 · 6H2O = (NH4)3HP2O7 · H2O >> Ca2P2O7. However, for the two basic soils, hydrolysis rates were: CaH2P2O7 > Ca3(NH4)2(P2O7)2 · 6H2O > (NH4)3 HP2O7 · H2O > > Ca2P2O7. Pyrophosphates were hydrolyzed more rapidly in acid soils than in basic soils.Application of 2% CaCO3 reduced hydrolysis rates of the acid soils. The same application of CaCO3 to the basic soils either slightly increased or had little effect on the hydrolysis rates.