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Figure 8. Irrigated Acres by Crop Type -Adams County <br />Adams County Crop Type Comparison <br />30000 <br />25000 <br />20000 <br />15000 <br />10000 <br />5000 <br />^~~ ^~~ ^~~ ^~~ ^~~ ^~~ ^~~ ^~~^ ^~~~ ^~~ ^~~ ^~~' ^~~' ^~~ ^~~ ^~dP ^~~ tied` ~oc9` <br />Ag Stat Corn Ag Stat Grains Ag Stat Alfalfa <br />Ag Stat Beans Ag Stat Sugarbeets Ag Stat Pasture <br />~ GIS Corn • GIS Grains GIS Alfalfa <br />GIS Beans ~ GIS Sugarbeets + GIS Pasture <br />Approach and Results -GIS Irrigated Acreage Coverages <br />In order to determine how AgStats could be used to estimate acreage for years with no <br />GIS coverages, trends in the GIS irrigated acreage were compared to the changes and <br />trends in the AgStats. As noted above, GIS irrigated acreage coverages were provided for <br />1956, 1976, 1987, and 2001. Coverages from 1976, 1987, and 2001 contained <br />information on crop type and irrigated acres. The 1956 coverage originally only <br />contained information on irrigated acres. <br />Some ditches span several counties. Therefore, two techniques were used to assign the <br />GIS irrigated acreage to a county4. "GIS by Ditch" assigned the ditch to the county that <br />contained the majority of the irrigated acreage under that ditch. "GIS by Location" <br />assigned irrigated acreages to a county based on the spatial location of the irrigated parcel <br />of land, in which case parts of ditches may be represented in more than one county. <br />Figures 1 through 8 also contain information on the four GIS irrigated acreage coverages. <br />GIS coverages indicate that basin-wide, irrigated acreage remained relatively constant at <br />around 1 million acres from 1956 to 1987 (Figure 1) and that between 1987 and 2001, <br />irrigated acres dropped to around 910,000 acres. <br />Figures 1 through 4 and Table 1 also indicate that GIS estimates of total irrigated acres at <br />both the basin and county levels are significantly less than AgStat estimates of irrigated <br />acres. Figures 5 through 8 provide an opportunity to take a closer look at changes in crop <br />type over time. These figures suggest that the largest discrepancy between the GIS <br />coverages and AgStats occurs in estimates of irrigated acres of corn. <br />AgStat and GIS estimates of acres of beans, grains, sugar beets, alfalfa and pasture are <br />relatively consistent. Note that although most crops have both "irrigated" and "non- <br />a According to AgStats, there is an attempt to have large users split their acreage up by county, however, it <br />is recognized that most users report their acreage under one county regardless. <br />Page 5 of 11 <br />