Tillage-induced environmental conditions in soil and substrate limitation determine biogenic gas production

Tillage changes soil environmental conditions and controls the distribution of residues in the soil, both actions that affect the production and emission of soil biogenic gases (CO2, N2O, and CH4). The objective of this study was to determine how tillage-induced environmental conditions and substrate quality affect the mineralization rate of easily metabolizable compounds and the subsequent production of these gases. Carbon compounds, with and without nitrogen, were applied to soil cropped to maize under tilled and no-till systems. Following substrate application in the spring and summer, biogenic gases were measured periodically at the soil surface (flux) and within the profile (concentration) at 10-, 20-, and 30-cm depths (i.e., within, at the bottom of, and below the plough layer). Strong CO2 and N2O responses to sucrose and glycine in both the field and the laboratory indicate that the soil was C- and N-limited. Surface fluxes of CO2 and N2O were greater in soils amended with glycine than with sucrose and were greater in tilled than no-till soils. Transient emission of CH4 following the addition of glycine was observed and could be attributed to inhibition of N mineralization and nitrification processes on CH4 oxidation. Laboratory and field measurements indicated that the larger substrate-induced CO2 emission from the tilled soils could not be attributed to differences in the total biomass or the basal respiratory activity of the soils. Thus, there appears to be no underlying difference in the functional capacity of the microbial communities under different tillage regimes. Comparison of gas profiles indicates relative accumulation of CO2 at depth in soils under no-till, as well as greater decline in profile CO2 content with time in the tilled compared to the no-till soil. These results support the conclusion that greater CO2 efflux from the tilled soils resulted from more rapid gas diffusion through the profile. Hence, the observed differences in gas fluxes between tilled and no-till soils can be attributed to differences in physical environment. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved.