climatic overlay to determine if any units had excessive ranges in
precipitation and temperature. Black and white composites and color
infrared imagery were used to refine preliminary boundary lines.
The subsequent parts of this section describe the evaluation and
analytical criteria applied to a developed APU. Additionally, initial
results of this evaluation are summarized.
B. Evaluation of Agrophysical Units
1. Test Area Description and Analysis Summary
Figure 2 is the APU map for the Great Plains. There are a total
of 29 strata, 4 of which contain less than 5 percent cultivated
land (1-1, 1-2, 1-3, 1-4).* For each APU, the land use, soils,
climate, and geology can be described in detail. These factors
play an important role in wheat area, yield, and production.
Figure 3 is a June 12, 1976, Landsat image depicting three APU's
located in the Texas and Oklahoma Panhandles. Examination of
the boundary lines for APU 60 indicates that these lines are
separating highly contrasting areas. This APU is located in the
Rolling Plains Land Resource Area while APU 4 and APU 9 are
within the High Plains Land Resource Area. APU 60 contains
shallow soils, located on 0-16 percent slopes, that have a lime
(CaC03) accumulation within a 40-inch depth. The soils in APU 4
and APU 9 are moderately deep to deep, situated on 0-8 percent
slopes.
The intensity of agriculture and cropping practices differs
greatly between the three APU's. Two-thirds of the area in
APU 9 are cropland. Under dry-land farming, winter wheat is
grown on summer fallowed land. Corn and sorghum are the main
irrigated crops. Changes in land use, such as increased cir-
cular irrigation, can be easily monitored within this APU.
In APU 60, the cropland is less than 10 percent of the total
area. Livestock farming is the principal enterprise with much
of the area in rangeland.
APU 4 contains intensive agriculture with the majority of the
cropland in irrigation. Major crops under irrigation are cotton,
grain sorghum, and winter wheat.
2. Evaluation Results
a. Agricultural Sampling Frame. During 1975, there were
601 randomly selected 8 km by 9.5 km sample segments F:
*Strata 1-1 contains more than 5 percent agriculture but lies out-
side the LACIE area of interest so was treated as non-agriculture.
