Tillage and crop residue effects on carbon dioxide evolution and carbon storage in a Paleustoll

Cultivation, high temperatures, and a semiarid climate accelerate organic carbon (OC) loss and weaken soil structure in the Southern Plains. Our hypothesis was that differences in soil C storage attributable able to tillage method are related to differences in soil respiration and microbial biomass dynamics. Carbon dioxide fluxes following wheat (Triticum aestivum L.) harvest were determined in Bethany silt loam (fine, mixed, thermic Pachic Paleustoll). Treatments were moldboard plowing (MP) and no-till (NT) at two residue rates (0 and 4 Mg ha(-1)). Soil respiration was measured from 1 August to 30 September using closed chambers. Peak CO2-C flux densities reached 1.3 g m(-1) d(-1) in NT for 2 d and stabilized at 0.4 g m(-1) d(-1). The CO2-C evolution peaked at 4.1 and 2.9 g m(-1) d(-1) in MP with and without buried residues, respectively. After 3 d, they decreased to a steady state of 0.4 g m(-1) d(-1). Daily average temperatures in the 0- to 0.2-m depth were 0.5 to 3.4 degrees C higher under MP than NT, increasing microbial adenosine triphosphate (ATP), biomass C, and CO2-C fluxes. The proportion of soil OC respired in the 60-d period was twice as great under MP than NT, accounting for 0.42 to 0.58% and 0.19 to 0.22%. respectively. After 11 yr, NT soil OC showed increases of 65, 17, and 7% over the MP for the 0- to 0.05-m, 0.05- to 0.1-m, and 0.1- to 0.2-m depths, respectively. Tillage and residue incorporation en enhanced C mineralization and atmospheric fluxes, suggesting that tillage intensity should be decreased to reduce C loss.