Effect of long-term fertilization on the forms of organic phosphorus in paddy soil derived from red earth

Based on the longterm fertilization experiment (19 years) in paddy soil derived from red earth, the method of Bowman and Cole (1978) was applied to study the effect of longterm fertilization on the forms and change of organic phosphorus in paddy soil The results showed that the organic phosphorus contents were 225.93 to 322.47 mgkg-1 in surface soil, accounting for 28.59% to 42.34% of the total P. In the various forms of organic P in paddy soil, MLOP was highest (13480 mgkg-1), accounting for 51.58% of total organic P, followed by MROP (92.46 mgkg-1, 35.38%), HROP (20.35 mgkg-1, 7.79%), and LOP (13.67 mgkg-1, 5.23%) In the treatment of no P application, it mainly caused the contents of MLOP and MROP to decrease, and the decreased amount was CKNK. MROP and HROP contributed most to the increase of organic P with continual P application, and the order of the increase was NPK+OMPNPK The change rate of organic P was different from that of inorganic P under different fertilization treatments The ratio of organic P to inorganic P rose in the no P application, but declined in the continual P application The P supplying capacity was negatively correlated with the organic P/inorganic P ratio (r=-0.9497* ,r0.05=0.878)