Quantitative studies on changes in C/N ratio,N,P,K.Ca and Mg contents of red clover and rye grass residues during decomposition in agroecosystems under no-tillage (NT) and conventional tillage (CT) were carried out in Horseshoe Bend,Ga,USA.Results showed that the decomposition patterns and mineralization rates of nutrients in the crop residues were different in the two ecosystems.Both the mineralization and biological immobilization of elements toolz place earlier in CT system than those in NT system.It was found that the amounts of nutrients elements remaining in residue,decreased rapidly in CT systems.