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58 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1916.
and silt loam. The loam, however, is more easily plowed and kept
in good tilth. Irrigation is practicable, and some of the type near
Sloan School, about 14 miles southwest of San Saba, has been under
irrigation for 30 years or more. At this place ribbon cane has
been grown under irrigation for a number of years, and an excellent
quality of sirup produced.
The following table gives the result of mechanical analyses of
samples of the soil and subsoil of this type:
Mechanical analyses of Frio loam.
Number. Description. Fine Coarse Medium Fine Very fine Silt. Clay.
gravel. sand. sand. sand. sand.
Per cent. Per cent. Per cent. Per cent. Per cent. Per cent. Per cent.
444639........... Soil ......... 0.3 4.6 5.7 24.1 20.0 30.8 14.5
444640 ........ .. Subsoil .... 28.0 2.8 4.2 22.6 20.2 32.4 17.9
The following samples contained more than one-half of 1 per cent calcium carbonate (CaCO3): No.
444639, 21.13, and No. 444640, 31.52 per cent.
FRIO SILT LOAM.
The Frio silt loam consists of a brown to dark-brown silt loam,
which passes at about 8 to 12 inches into brown or chocolate-brown
silty clay loam of moderately friable structure. Both the surface
soil and subsoil effervesce freely with acid, apparently being notably
calcareous.
The type as mapped includes near the banks of the streams small
areas of loam and sandy loam and elsewhere much soil closely approaching
a silty clay loam in texture. Also in places there are
narrow strips of coarser and sandier soil, resulting from colluvial
wash from the higher lying terraces occupied by the Miles soils.
The Frio silt loam occupies the greater part of the bottom land
along the San Saba River for a distance of 6 to 8 miles west of San
Saba. Elsewhere it does not occur in areas large enough to be
mapped on the scale used in the survey. The land is nearly level,
but the elevation of 25 to 30 feet above the river level insures sufficient
natural drainage for farming. The topography is favorable
to the use of farm tractors, and practically all the type is irrigable.
The total area of this type is small, but the greater part is under
cultivation. The uncleared land supports a rather open growth of
pecan, elm, hackberry, and china berry near the river and a rather
thick growth of mesquite on the drier land. Good pasturage is
afforded in both winter and summer. The crops grown, the yields,
and the farming methods are about the same as on the silty clay
loam type of this series. The silt loam, being lighter in texture
and naturally somewhat looser and mellower, is easier to till than