practices change annually and seasonally), data collection programs should be completed quickly to create a database that is, ideally, specific to a given year.
Ideally, management factors such as plant growth, tillage and other soil disturbances with their associated ground cover conditions, irrigation, drainage, conservation practices, grazing, and agrichemical applications should be considered when conducting a ground water vulnerability assessment (USDA 1992). Not all these factors are described in national or regional databases; however, several databases are worthy of note because they address some of these factors, including the National Resources Inventory, the National Agricultural Census of 1987, the Irrigation Water Use Survey of 1988, and several pesticide databases.
The National Resources Inventory (NRI) is a multiresource inventory conducted at five-year intervals by the SCS. Data are collected at approximately 800,000 points on nonfederal lands and include information on soils, land cover, land use, cropping history, conservation practices, conservation treatment needs, potential cropland, prime farmland, highly erodible cropland, water and wind erosion, wetlands, wildlife habitat, vegetative cover conditions, irrigation, and flood susceptibility. In 1982 and 1992, sufficient sample information was collected to characterize major land resource areas (MLRAs). In 1987, however, fewer areas were sampled allowing for good characterization at the state level. For nonfederal lands, the NRI is one of the most comprehensive and consistent databases for national resource analysis and is one of the few that links soil type with management factors such as conservation practices, land use, land cover condition, and irrigation.
The Bureau of the Census conducts an agricultural census every five years. The 1987 census includes statistical information by county about farm numbers, farm value, farm size, market value of agricultural products, farm income, farm expenses, farm land use, farm irrigation, agricultural chemical use, livestock and poultry operations, crops and vegetables harvested, fruits, nuts, and berry production, and nursery and greenhouse crops.