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Recommendations for the Use of CASS and NASS Data <br />Based on the information obtained regarding the CASS and NASS reporting, we recommend the <br />following use of both sources of data to 1) compare to acreage estimates developed in the SPDSS <br />Irrigated Acreage Assessment, and 2) to estimate acreage and crop types for years between <br />Irrigated Acreage Assessments (to be completed in subsequent phases). <br />^ Annual CASS data should be used to identify and quantify crop types specifically <br />reported at the County level. These crop types are those listed in Table 2. <br />^ Because the data collected and summarized in this task are to assist in the Irrigated <br />Acreage Assessment, only acreage from the CASS "Irrigated" category should be <br />included for each crop type. <br />^ Irrigation water is often applied to crops that are not harvested, due to a dry-year supply, <br />hail damage, etc. Therefore, acreage from the "Planted" category should be included for <br />each crop type, when available. Note that for perennial crops, such as alfalfa, acreage is <br />often only provided under the "Harvested" category. <br />^ NASS data should be used for total vegetables grown by County for the years reported. <br />^ Grass Pasture should be estimated by combining NASS data for irrigated pasture grown <br />by County for the years reported with CASS data for "Hay Other". CASS "Hay Other" <br />category is described as grass crop that generally "hayed" and sold. NASS irrigated <br />pasture category is described as grass crop that is left in place for grazing or cut for on- <br />farm use. <br />Major Crop Types <br />Crop types can be characterized by growing season (planting and harvesting dates), irrigation <br />water requirement, and spectral signature from multi-temporal satellite image analyses. The <br />growing season and irrigation water requirement are greatly affected by climate. For the RGDSS <br />irrigated acreage assessment, several crop types with spectral signatures difficult to distinguish <br />were combined into a "small grains" category. These crop types -barley, oats, and wheat - <br />could be combined because they have similar growing season and irrigation water requirements. <br />The following approach was taken to determine appropriate major crop types or groups: <br />1. Major crops grown in each county were identified from the CASS and NASS data. <br />2. Growing season and irrigation water requirements published by the Colorado Irrigation <br />Guide were reviewed to determine the potential for crop groups. <br />3. SCS TR-21 recommended growing season beginning and ending average temperatures <br />were reviewed to determine the potential for crop groups. <br />4. Crop groups were considered for crops with similar irrigation water requirements if it <br />was also difficult to distinguish the spectral signature from the multi-temporal satellite <br />image used by the GIS contractor to estimate crop types. <br />Page 6 of 13 <br />