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Soil Carbon Stocks Across an Irrigation Chronosequence |
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| Irrigation dramatically changes the productivity of cropland in arid and semi-arid regions, resulting in much higher yields as well as greater amounts of crop residues that are returned to the soil. In addition, organic matter decomposition and the flow and redistribution of nutrients and soluble organic matter in the soil are greatly altered by irrigation. Consequently, the C cycle, and potential for carbon sequestration, of irrigated cropland is fundamentally different from non-irrigated crops and native vegetation. Finally, irrigation can have other effects of agricultural greenhouse gas emissions by impacting energy use (e.g. for pumping) as well as emission rates of other soil-derived greenhouse gases such as nitrous oxide (N2O) and methane (CH4). | ||
| To study the effects of irrigation management on soil carbon stocks we are doing a series of paired-plot comparisons of carbon, between irrigated, non-irrigated fields and rangeland at sites selected across Eastern Colorado and Nebraska. We will be sampling fields within the same area that have been under irrigation for varying lengths of time (e.g., 10, 20, 30 years or more). Thus we will be able to quantify changes in soil C stocks over time following introduction of irrigation and compare those to non-irrigated and native rangeland systems. | ||
| We are using LANDSAT thematic mapper (TM) imagery and state well/irrigation records to select sites that represent chronosequences (that is, time histories) of irrigation use across the region (see example figure). In Nebraska we have already compiled overlays of GIS coverage of irrigated area with TM land cover. The Nebraska state irrigation records provide information on the location, date of initiation and water use for all registered wells in the state since the 1960's and there is information on land areas irrigated by surface water prior to that time. Thus the maps will be used to locate fields where irrigation was initiated, 10, 20, 30, or 40 years previously, and these can be overlain with soils maps to construct chronosequences on different soil types. Similar data exist in Colorado and will be analyzed during the course of the experiment. After field site selection, samples will be taken in adjacent irrigated and non-irrigated sites and permanent grassland, where appropriate never-tilled reference sites exist. | ||
| Average annual water use and depth to aquifer data will be used to estimate energy costs associated with irrigation. We will also conduct interviews with landowners, where possible, to validate data on water use and to collect information on N fertilizer and manure applications. This information will provide a broad-based regionally applicable database that will be complemented by the more measurement-intensive studies described above. The work is being carried out by investigators at Colorado State University in collaboration with CASMGS scientists at University of Nebraska and USDA’s Natural Resource Conservation Service. | ||
| The following images show SSURGO soils, landuse and well locations: green - irrigated cropland, caramel - range, tan - dry land, pink - urban areas | ||
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