MANAGEMENT-INDUCED CHANGE IN LABILE SOIL ORGANIC-MATTER UNDER CONTINOUS CORN IN EASTERN CANADIAN SOILS

Soil samples taken from four experimental sites that had been cropped to continuous corn for 3-11 years in Ontario and Quebec were analyzed to evaluate changes in quantity and quality of labile soil organic car bon under different nitrogen (N) fertility and tillage treatments. Add i tion of fertilizer N above soil test recommendations tended to decre ase amounts of water-soluble organic carbon (WSOC) and microbial bioma ss carbon (MBC). The quality of the WSOC was characterized by C-13 nuc lear magnetic resonance and infrared spectrophotometry and the results indicated that carbohydrates, long-chain aliphatics and proteins were the major components of all extracts. Similar types of C were present in all of the soils, but an influence of management was evident. The quantity of soil MBC was positively related to the quantities of WSOC, carbohydrate C, and organic C, and negatively related to quantities o f long-chain aliphatic C in the soil. The quantity of WSOC was positiv ely related to the quantities of protein C, carbohydrate C, and negati vely related to the quantity of carboxylic C. The quantity of soil MBC was not only related to quantities of soil WSOC but also to-the quali ty of soil WSOC.