Abstract: Field experiments were conducted to study the dynamics of soil organic carbon, total nitrogen and nitrate in plowed layer of spring corn and spring wheat fields under straw and plastic film mulching. The results indicate that straw mulching significantly increases soil organic carbon content during growth periods of spring corn and spring wheat. However, organic carbon content decreases under plastic film mulching. Irrigation reduces both the decline degree under plastic film mulching treatment, and the increase degree in straw mulching treatment of soil organic carbon during the growth periods of spring wheat. Soil total nitrogen and nitrate contents show "increase-decrease-increase" trend under both straw and plastic film mulching during growth periods of spring corn and spring wheat. However, the change range in soil total nitrogen, which is not significantly different among treatments, is much smaller than that in soil nitrate, which is significantly different among treatments. The effect of irrigation on soil total nitrogen content is insignificant for all mulching treatments during growth period of spring wheat, but it significantly limits the degree of increase in soil nitrate for all mulching treatments at jointing stage of spring wheat.