Impact of no-tillage agricultural methods on the energy balance and the greenhouse gas balance of cropping systems

Abstract

A presentation of different measurements of decreased energy consumption achieved by reduced-or no-tillage is followed by an analysis of the energy balance and greenhouse gas (GHG) emission balance drawn from the long-term trial at Boigneville in the Basin of Paris (France). The estimated decrease in annual fossil fuel consumption was 28 L/ha under superficial tillage and 41 L/ha under direct seeding. These data are consistent with data collected elsewhere which indicate that reduced tillage, as compared with conventional tillage methods, allows an average saving of 20 L/ha/yr of fossil fuel in loamy or silt-clay soils. This saving can be doubled in clay soils. Energy expenditure in the cropping system as a whole was thus reduced by 6 to 11%. The energy saving is much lower (1-1.5%) when the balance includes energy stored in the harvested biomass, as, in this situation, biomass yield is not affected by reduced-or no-tillage practices. Reduced-or no-tillage practices had a positive effect on the balance of GHG emissions by reducing fuel consumption and increasing carbon storage in the soil. However, this beneficial effect was counter-balanced by the increase in N2O emissions measured under reduced tillage. The overall GHG balance on the site indicated an increase in CO2 storage of about 200 kg ha/yr under reduced tillage or direct seeding. This resulted from the balance between carbon and N2O fluxes which have contradictory effects and are known to be extremely variable. Slight variations in these fluxes could strongly modify the conclusions drawn from our observations. Further studies are required to corroborate these data before they can be extrapolated.