Long-term impacts of different tillage intensities on the C and N dynamics of a Haplic Luvisol

The objectives of the study were to quantify the effects of 40 years of conventional tillage (CT) and reduced tillage (RT, maximum tillage depth of 8 cm) on C and N dynamics in the surface (0-5 cm) and subsurface (5-25, 25-40 cm) soils of a silty Luvisol in a long-term trial at Garte Sud, Germany (temperate climate). Stocks of C and N and contents of microbial biomass C and N were significantly higher in the surface soil of the RT treatment than in the CT treatment. However, over the entire profile (0-40 cm), C and N stocks did not differ significantly. Cumulative net N mineralization (determined in a laboratory incubation at 13.7 degrees C and 60% water holding capacity) was significantly higher in the surface soil of RT (58.6 mg kg(-1)) than that of CT (26.7 mg kg(-1)), whereas in the subsurface soil depths, cumulative N mineralization was higher in the CT treatment. By contrast, gross N mineralization rates did not generally differ significantly between the treatments. Overall, different tillage intensities affected C and N dynamics only slightly in the entire profile because increases in C and N stocks and N mineralization rates in the surface soil of RT were counterbalanced at greater depths.