Understanding soil greenhouse gas fluxes in intensive maize-based cropping systems

A field and three laboratory experiments were conducted to measure emissions of greenhouse gases in intensive irrigated maize-based systems managed at high yield levels with a view to understand how soil greenhouse gas productions are influenced by biogeochemical processes and crop management practices. Emissions ranged from 0.23 to 116 g N2O-N ha-1 d-1 and 0.18 to 54.8 kg CO2-C h-1 d-1 for recommended cropping systems (CCP1M1 and CSP1M1) and 0.93 to 162.8 g N2O-N ha-1 d-1 and 1.03 to 52.3 kg CO2-C ha-1 d-1 for intensive cropping systems (CCP3M2 and CSP3M2). Average annual N2O emission estimate in intensively managed CC and CS rotations was 7.5 kg N2O-N ha-1 yr-1 while average annual estimate in the recommended cropping systems (CCP1M1 and CSP1M1) was 5.5 kg N2O-N ha -1 yr-1. Seasonal N2O emission peaks were associated with high soil NO3 content, EC, soil/air temperature and water content. Average annual CO2 emission estimates in both levels of cropping management were 5.3 Mg CO2-C ha -1 yr-1 for CS rotation and 6.8 Mg CO 2-C ha-1 yr-1 for CC rotation suggesting that the CO2 emissions were significantly influenced by the amount and kind of crop residue returned to the field from the previous crop.; The close relationship between soil electrical conductivity and N 2O and CO2 emissions in the field was further studied in the laboratory soil cores from six soil series (Kennebec, Floyd-Webster, Cecil, Sharpsburg, Yolo, and Valentine soils) at 0.5, 1.0, 1.5, 2.0 dS m -1 soil EC and 60% and 90% WFPS. In general, increasing soil EC values from 0.52 dS m-1 to 2.02 dS m-1 decreased the production of N2O via nitrification at 60 WFPS. However, at 90% WFPS, rates of N2O production were directly related to soil EC values. Possible reasons for such an inverse relationship include: a change in the activities/functions of microbial communities, decrease of bioavailable C and N following salt addition and the ability of bacterial cells to tolerate water and salt stress conditions. Based on the laboratory study of field soils, there was a 26% reduction of N2O emissions when a slow-release form of N fertilizer (ESN) was applied in the soil rather than NH4NO3. (Abstract shortened by UMI.)...