22 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 
If the terrace has a fall greater than one-half foot per 100 feet, 
erosion occurs above the terrace, a channel is scoured out and it 
develops practically into a hillside ditch. Although this type of 
terrace is used extensively in the Piedmont region of the South, it 
is being supplanted rapidly by forms of the broad, cultivated terrace. 
The broad-base form.—The broad-base graded terrace, generally 
known as the Mangum terrace, has been adopted in many sections of 
the country for the reason that the entire terrace bank can be culti- 
vated—thus utilizing all land and preventing growth of objection- 
able weeds and grass. This terrace can be crossed readily at any 
angle in planting and cultivating crops with large farm machinery. 
When it is intended to use such machinery and to cross at an angle, 
the terrace must be made broader than when all farming operations 
are in lines parallel with the terrace. The following tabulated values 
are the results of surveys of terraced fields of the Mangum type near 
Wake Forest, N. C.: 
Actual dimensions of Mangum broad-base graded terraces. 
Field averages. 
Absolute | Absolute 
Dimension. minimum. | maximum. 
Minimum. | Maximum. 
IBASe width Ofberrace sac eosin eeinccing te ecie ce eeer feet.. 25 50 30 33 
Ieeight OLbEREACe: ie eeu eae mine se sna iaicea feet... 58 1 ao 8 
Vertical distance between terraces.......-...-..-- feet... 2 8.9 2.8 Ze 
Men ethiorberracee ay se eee eee sc pencee eno ee eee feet... 450 250! t lleaeres SS Arey AES EA 
Grade of terraces 245 6 te bec des terete eee per cent... 1.69 2. 24 2 a | 
lope of land Suriace eo. cols Sea cose we per cent. . 4.7 18. 2 5 14 
These fields appeared as series of broad waves. On the steepest 
slopes, where one terrace slope ends the next one begins, the whole 
field being a succession of terraces. (See fig.2, E and F.) The rows 
were run parallel with the terraces shown in figure 2 E; on a less 
steep slope (fig. 2 F) the rows crossed the terraces. 
Surveys were made also of a number of fields with graded terraces 
where the crop rows always were parallel with the terraces. The 
results obtained are shown in the following table: 
Actual dimensions of broad-base terraces wnere rows are parallel with terraces. 
Field averages. 
Absolute | Absolute 
Dimension. minimum. | maximum. 
Minimum. | Maximum. 
BASCOM WIT HOLLOTTACR see eee ee ee ee ee moras Emaar feet... nae 19 7.8 15.5 
FI CISH OL CETLACE eateries sia teem awie Ae relcle ee cio tis feet... 4 1.8 sr Weak 
Vertical distance between terraces. --.- mai Cee Nate feet... 2 9.2 2.9 8.3 
ene LIMOULCITACS selena eas ale ioe orn nin Sik late imine te feet... 200 E800) 5, A] Ssicmmters a roteel See eee eeneetete 
Grade onterracesse ee sece bakes elneeh ied = peters per cent.. mA 2. 24 .3 2 
Slope OMandisuriace ese. seen aces & eee per cent... 3.4 20 4.4 14 
