26th Southern Conservation Tillage Conference SOIL RESPIRATION RATES AFTER 25 YEARS OF NO-TILLAGE

Long-term conservation tillage management results in changes in the chemical and physical properties of soil, which likely affect CO2 flux rates to the atmosphere. Our objective was to compare respiration rates of soil that had been in no-tillage management for 25 yrs to soil that was managed with conventional tillage. Soil respiration was measured in disked and no-tillage plots in 2003 on a Norfolk loamy sand soil (fine-loamy, siliceous, thermic Typic Kandiudult). This tillage experiment was established in 1978 and the surface 2-in of the no-tillage and disked tillage plots differed in soil C content. Measurements were collected for approximately 50 days during the summer and during the fall. Soil respiration rates during the summer ranged from 0.6 to 22.7 gm CO2 m-2 hr-1 for disk tillage and from 0.6 gm to 1.4 gm CO2 m-2 hr-1 for no-tillage. Soil respiration rates in the fall ranged from 0.3 to 3.7 gm CO2 m-2 hr-1 for disk tillage and from 0.2 gm to 0.6 gm CO2 m-2 hr-1 for no-tillage. Respiration rates within a season were highly dependant on soil water content, especially following disk tillage. Although respiration rates were usually much lower for no-tillage, the two tillage systems had generally had similar coefficients of variability for soil respiration. Low respiration rates with conservation tillage even after 25 yrs suggests that intensive cropping with high residue crops should cause the surface soil organic matter content to continue to increase