Appendix B 

 CN Memo -23 



PROCEDURES USED IN OBTAINING FIELD DATA AND DETERMINING ESTIMATES 



Land Use and Conservation Treatment Needs 



The basic data for the updated Inventory of Conservation Needs in 

 Montana have been developed from soil surveys. 



The system adopted for updating the inventory involved recording 

 appropriate data in the sample areas being reexamined. 



The randomized samples representing every county and selected by the 

 statistical laboratory at Iowa State University were the areas re- 

 examined. The sample units were located on county base maps with a 

 scale of 1 inch to 2 miles, or larger. The map showed the boundaries 

 and symbols of land resource units and soil conservation districts. 

 Watershed boundaries were shown where they were known, or they were 

 added later. If there was Federally owned land in the county, its 

 boundaries were shown, except where this ownership was inter- 

 spersed with private lands in small tracts of one section or less 

 in size. 



The standard size of sample units was 160 acres. The basic sampling 

 rate was 2 percent. As a standard, the statistical laboratory selected 

 two separate sets of sample units in each county. Each set represented 

 approximately 2 percent of the county area. 



In a county or other area of 250,000 to 500,000 acres, a 2 percent 

 sampling provided data of an acceptable degree of reliability. In 

 counties of this size, therefore, it was necessary to map only one set 

 of sample areas. In lareer areas the rate was reduced, but in smaller 

 areas it was increased to maintain the same level of reliability. 



In updating the inventory in 1966-67, a different system was used for 

 obtaining more data from the sample areas. The previous inventory ob- 

 tained from the sample areas the acreages of the four major land uses 

 by land capability classes and subclasses. In updating the inventory, 

 conservationists also obtained the conservation treatment needs for 

 cropland and pasture and range. Each sample area was marked with ran- 

 dom points (36 points for 160 acre sample area) at which the conserva- 

 tionist inspected the conditions and recorded the data on the Sample 

 Area Record (see Form SCS-263) by codes for the land uses and conser- 

 vation treatment needs. 



Land use determinatioiis at each designated point were in terms of the 

 field in which the point fell. The use of the land in the vicinity 

 of the point was considered as well as the area at the point itself. 



156 



