10 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 
spacing should be used. For the 3-foot spacing a greater number of 
terraces are required and narrower benches result, but the terraces are 
easier to build and maintain than for a greater spacing. However, 
many farmers favor the wider benches because of the fewer terraces 
required and the fact that it is more convenient to cultivate the field 
in a few broad strips than in a greater number of narrow ones. In 
other words, they are willing to incur a greater loss by erosion for the 
sake of greater convenience in cultivation. 
The slope of the terrace bank, or the ratio of ¢ to d, was found to 
range from 58 to 121 per cent. Tt j is believed that this bank could be 
maintained easily at a slope of $ to 1, or 50 per cent. This would 
reduce the area of waste land in a terraced field. 
The curves in figure 4 show the widths of bench for different ver- 
tical spacings on land of various slopes. Each curve is drawn for 
a certain vertical spacing between terraces. The widths of bench are 
computed for horizontal-bench terraces having a slope of $ to 1 for 
the terrace banks. When constructed and maintained properly, 
bench terraces give excellent protection against erosion. However, 
many landowners object to this terrace on account of the difficulty 
of moving farm machinery from one bench to another, the necessity 
of cultivating each bench separately, the loss of the land occupied 
by the uncultivated embankments, and the growth of weeds and 
grass on the embankment, which robs the adjacent cultivated soil 
of its plant food and tends to seed the entire field to weeds and ob- » 
jectionable grasses. These reasons are sufficient to militate against 
the use of this terrace except on steep slopes where no form of cul- 
tivable terrace can be employed. 
The best practice indicates that the bench terrace should not be 
used on slopes exceeding 20 per cent. However, they are actually in 
use on slopes up to 30 per cent, with a vertical interval of 8 to 10 feet; 
but in such instances the labor of cultivating the narrow benches and 
of maintaining the high embankments is considerable, and it is be- 
lieved that such slopes could be devoted more profitably to pasture 
or timber. 
THE LEVEL-RIDGE TERRACE. 
The narrow-base form.—The narrow-base level-ridge terrace (see 
fig. 2-B, and Pl. IV, fig. 2) 1s used to a great extent throughout the 
Piedmont region of the South. It is essentially the first stage in the 
construction of a bench terrace, but methods of plowing are em- 
ployed to prevent it from developing into a terrace of the bench 
type. It is built usually 3 to 5 feet wide at the base and from one- 
half to 1 foot high. Where these terraces are sodded heavily they 
render satisfactory service on pervious soils and slopes not greater 
than 5 to 8 per cent. They should be spaced from 2 to 3 feet apart 
in vertical distance. A close spacing reduces the volume of water 
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