CONVERSION OF AMMONIUM POLYPHOSPHATE (APP) IN ACIDIC SOIL AND ITS EFFECT ON SOIL PHOSPHORUS AVAILABILITY

To clarify the transformation of ammonium polyphosphate (APP) in acidic soil and its effect on soil phosphorus availability is prerequisite for the rational application of APP with different degrees of polymerization. The present study used industrial-grade monoammonium phosphate (MAP) as control, lateritic red soil and latosol were used as test soils, the soil culture experiments were conducted for 50 days. The effects of different fertilization treatments on soil availability and transformation of inorganic phosphorus forms in lateritic red soil and latosol were compared between three kinds of APP (APP1, APP2, APP3) with different degree of aggregation and APP3 with MAP (A3:M). Among them, APP1 (15-62-0) is ammonium polyphosphate mainly composed of low and middle polymer; APP2 (20- 43-0) is ammonium polyphosphate mainly composed of middle and high polymer; and APP3 (13-70-0) is evenly distributed. The results showed that (1) in lateritic red soil, the effect of APP1 alone was the best, while in latosol, the effect of A3:M on improving soil available phosphorus content was remarkable; (2) the available phosphorus content in lateritic red soil under fertilizer treatment was much higher than that in latosol; (3) the content of inorganic phosphorus in the two soil types were O-P Fe-P > Al-P > Ca-P.