10 BULLETIN 512, U. S. DEPARTMENT OF AGEICULTUBE. 



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 c to ^, was found to 

 range from 58 to 121 per cent. It 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-hase form: — The narrow-base level-ridge terrace (see 

 fig. 2-B, and PL IV, fig. 2) is 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 



