CLEMENS SCHEER1, REINER WASSMANN2, JOHN LAMERS3
1Center for Development Research, Bonn, Department of Ecology and Natural Resource Management, Germany
2Karlsruhe Research Center, Institute for Meteorology and Climate Research, Germany
3Center for Development Research (ZEF), University of Bonn, Germany
Agricultural systems in the Khorezm region (Uzbekistan, Central Asia) are characterised by monocultures under irrigation in combination with intensive fertilisation. Irrigation and fertilisation of arid systems not only stimulates plant growth, but also a variety of microbial processes enhancing the turn-over of soil carbon and nitrogen (N) leading to elevated emissions of greenhouse gases (GHG) such as N2O and CH4.
In 2005, GHG emissions were measured from experimental fields at 6 research sites, encompassing 5 different land use types. Emission rates from irrigated agricultural fields were high and represent a significant source of GHG due to N2O emissions from cotton and winter wheat as well as CH4 emissions from flooded rice fields. Even an unfertilised plantation of poplar trees showed surprisingly high N2O fluxes. In contrast, N2O emissions were very low in spots with native vegetation, i.e. the `Baday Tugai' riparian forest along the Amu Darya River.
The observed temporal patterns of N2O emissions were similar for cotton and winter wheat fields. Periods of very high N2O emissions were triggered by fertiliser application in combination with irrigation. These ``emission peaks'' accounted for 80% of the total N2O emissions over one cotton season. Cumulative N2O emissions during the cropping season varied between 2.5kg N2O-Nha-1 - 5.6kg N2O-Nha-1, which corresponds to 3.8% of the total fertiliser applied.
The common management practice of concomitant fertilisation/irrigation in combination with the high soil temperatures during the season leads to an elevated soil microbial activity. Subsequently, the farming systems in Khorezm experience high losses of N via denitrification. This implies low N use efficiency of the fertiliser applied and large emissions of N2O-gas. Modifications in the amount and timing and modalities of the fertiliser application in combination with improved irrigation techniques may improve the agronomic performance and reduce the environmental impacts.
Keywords: Emission, fertilisation, greenhouse gas, irrigation, N2O