Soil carbon dioxide and nitrous oxide emissions from an agricultural watershed as influenced by landscape position and agroforestry conservation management practices

Atmospheric concentrations of greenhouse gases, such as carbon dioxide (CO2) and nitrous oxide (N2O), have increased over the past two centuries. One major source of greenhouse gas emissions is agricultural soils. However, the effects of contour grass strips and contour grass-tree strips, on greenhouse gas emissions have not been extensively studied. The objective of this study was to determine the effects of landscape position and grass and grass-tree contour strips, on the efflux of soil CO2 and N2O across three agricultural watersheds in northeast Missouri. The three watersheds were in a corn-soybean rotation, and contained one of three management systems: (1) cropped only, (2) cropped with grass contour strips, or (3) cropped with grass-tree contour strips. Surface measurements of the two gases were collected during the 2004 growing season at three landscape positions. The N2O production from the cropped watershed (1.9 g N2O-N m-2) was 2.3 and 3.8 times greater than the agroforestry and grass watersheds, respectively. Across all three watersheds, the soil N2O production was lowest in the lower backslope position (0.7 g N2O-N m-2 ). Soil CO 2 production was lowest in the cropped watershed (0.9 kg CO2-C m-2) compared to the agroforestry (1.5 kg CO2-C m-2) and grass watersheds (1.5 kg CO2-C m -2). The lower backslope position (1.6 kg CO2-C m -2) across all three watersheds produced greater soil CO2 than the upper and middle backslope positions. The results of this study indicate that conservation management practices and landscape position have an effect on the soil surface efflux rates of CO2 and N2O. Permanent vegetative contour strips in an agricultural watershed may help mitigate the increasing levels of tropospheric CO2 and N2O.