Abstract: The transformation processes and control factors of the two main chemical forms（NO₃ -N,NH₄-N）of chemi-cal fertilizers in soil -water systems have been studied .The re-sults show that the two processes of mitrification and denitrifica-tion in the systems were all strong, and nitrification started earlier and goes faster than denitrification,The couple reaction of deni-trification and nitrification in soil-water system is the key mech- anism of the nitrogenous compound transformation,The main en-vironmental factor which control the degree of nitrite accumula-tion is temperature.

Key words: soil- water system, nitrogen, nitrification, denitrification, influencing factor