Influence of crop rotation and liming on greenhouse gas emissions from a semi-arid soil

Semi-arid lands represent one fifth of the global land area but our understanding of greenhouse gas fluxes from these regions is poor. We investigated if inclusion of a grain legume and/or lime in a crop rotation altered greenhouse gas emissions from an acidic soil. Nitrous oxide (N2O) and methane (CH4) fluxes were measured from a rain-fed, cropped soil in a semi-arid region of Australia for two years on a sub-daily basis. The randomised-block design included two cropping rotations (lupin-wheat, wheat-wheat) by two liming treatments (0, 3.5 t ha(-1)) by three replicates. The lupin-wheat rotation only received N fertilizer during the wheat phase (20 kg N ha(-1)), while the wheat-wheat received 125 kg N ha(-1) during the two year study. Fluxes were measured using soil chambers connected to a fully automated system that measured N2O and CH4 by gas chromatography. Nitrous oxide fluxes were low (-1.4 to 9.2 g N2O- ha(-1) day(-1)), and less than those reported for arable soils in temperate climates. Including a grain legume in the cropping rotation did not enhance soil N2O; total N2O losses were approximately 0.1 kg N2O-N ha(-1) after two years for both lupin-wheat and wheat-wheat rotations when averaged across liming treatment. Liming decreased cumulative N2O emissions from the wheat-wheat rotation by 30% by lowering the contribution of N2O emissions following summer-autumn rainfall events, but had no effect on N2O emissions from the lupin-wheat rotation. Daily CH4 fluxes ranged from -14 to 5g CH4-C ha(-1) day(-1). Methane uptake after two years was lower from the wheat-wheat rotation (601 g CH4-C ha(-1)) than from either lupin-wheat rotations (967 g CH4-C ha(-1)), however liming the wheat-wheat rotation increased CH4 uptake (1078 g CH4-C ha(-1)) to a value similar to the lupin-wheat rotation. Liming provides a strategy for lowering on-farm greenhouse gas emissions from N fertilised soils in semi-arid environments via decreased N2O fluxes and increased CH4 uptake. (C) 2013 Elsevier B.V. All rights reserved.