Based on long-term fertilization experiment for 26 years in paddy field

the effects of long-term fertilization on profile distribution of soil nitrogen and C/N

Soil nitrogen mineralization characteristics

nitrification rate and relationship between cumulative mineralization and effective accumulated temperature were studied

the result showed:(1) Topsoil nitrogen accumulation significantly increased

profile distribution curves of soil nitrogen were in 'S' shape.Total nitrogen contents of 0-20 cm soil layer of organic manure treatments were higher than that of chemical fertilizer treatments.In 20-30 cm soil layer

nitrogen content of CNP

CNPK and C0 was higher than MNP

MNPK

MRN and M0.There are little differences of nitrogen contents in 40-50 cm soil layer;(2) Soil nitrogen mineralization curves were significantly different in prophase.Mineralization of different treatments general reached maximum after 7 d and tended to be stable after 28 d.Mineralization of organic manure treatments was higher than that of chemical fertilizer treatments after 7 d.Cumulative mineralization and effective accumulated temperature were in good accord with effective accumulated temperature model.Mineralization constant K and n reflected that organic manure treatments may had more mineralization potentials and mineralization processes of chemical fertilizer treatments may require more time to reach stable state;(3) Nitrification rates of all treatments were increased

organic manure treatments were higher than chemical fertilizer treatments

CRN was higher than CNP and CNPK.Nitrification rate of MNPK was the maximum and increased 6.44 times compared with C0;(4) Organic manure and straw applications may result in C/N of topsoil decreased.For C/N of 0-10 cm soil layer

CNPK>MNPK

C0>M0

MRN was the lowest.For C/N of 20-50 cm soil layer

Organic manure treatments were general higher than chemical fertilizer treatments

and subsoil of chemical fertilizer treatments had higher degree of SOM decomposition.