FACTORS AFFECTING HYDROLYSIS OF POLYPHOSPHATES IN SOILS

We investigated the effect of 17 soil properties on hydrolysis of seven linear oligophosphates ranging from P2 to P65 and a cyclic polyphosphate (trimetaphosphate). Each of 29 Iowa surface soils was treated with 500 μg of polyphosphate P/g of soil and incubated under aerobic conditions at 25°C for 7 d, and the amount of orthophosphate (Pi) produced was determined. Results showed that polyphosphate hydrolysis varied with the oligophosphates and soils used. Statistical analysis of paired relationships showed that, with the exception of P2, the amounts of Pi produced from the individual polyphosphates were significantly correlated with soil pH and negatively correlated with dithionite-extractable Al3+ and Fe3+. The amounts of Pi produced from certain polyphosphates, but not the others, were significantly correlated with water-soluble Ca2+, but negatively correlated with pyrophosphatase activity (buffered and nonbuffered systems). Multiple-regression analyses showed that polyphosphate hydrolysis is affected by pH, water-soluble Ca2+ and nonbuffered pyrophosphatase activity, all of which had significant positive partial-regression coefficients. Soil properties that showed significant negative partial-regression coefficients were percentage of clay (all P compounds studied), water-soluble Mg2+ (P2, P3, TMP, P5, P15, and P25), and dithionite-extractable Al3+ (P2, P5, P15, P25, P35, and P65). The R2 values of these regression equations ranged from 0.66*** to 0.88***.