Decomposition experiments were carried out under field conditions in Wu-xi district,JIangsu province with 13 kinds of plant residues such as the straws of cereal and leguminous crops including green manure plants,most of them are usually grown in Tai-lake basin.Under favorable conditions,the decomposition of plant materials proceeded much more rapidly in the first month,then became slower gradually and retained almost unchange untill the 2nd and even 3rd year.The difference among the amounts of C decomposed from different plant residues was greatest in the initial 1-3 months,whereas their difference could be found apparently even in third year.