A fifteen-year field trial (started in 1990) was conducted to determine the inorganic P fractions under 8 classical modes of fertilization in the lower reach of Liaohe River Plain. The results showed that Ca2-P, Ca8-P, Al-P and Fe-P decreased in the absence of P application, while increased with supplemental P addition. Interestingly, O-P and Ca10-P, with low bioavailability, increased at different levels under all treatments after 15 years. The contents of inorganic P were low in crop stalk, indicating that P supplying capacity was weak. On the contrary, both fresh pig excretion and decomposed manure were huge inorganic P pools.