10 MISC. PUBLICATION 6 5 6, U. S. DEPT. OF AGRICULTURE 



The research has been planned and carried out cooperatively with the 

 State experiment stations of Maryland and North Carolina. In Mary- 

 land, studies have been located at the Beltsville research center; in 

 North Carolina, they have centered on the Soil Conservation Experi- 

 ment Station near Raleigh. In both areas field trials and supple- 

 mentary studies have been carried out on farmer-operated fields. The 

 practical results of this research are presented and discussed in the 

 following paragraphs. 



Row Grades on Bright-Tobacco Soils 



The principal experiment on row grades at the station near Raleigh, 

 N. C, was conducted to determine the grade for tobacco rows that 

 would result in effective row drainage, protection against soil loss, and 

 good crop yields. Highly ridged crop rows were used with well- 

 defined drainage channels between rows. Six variations of grade were 

 tested, ranging by 6-inch intervals from to 30 inches per 100 feet. 

 The plots were laid out on typical bright-tobacco soil of Appling and 

 Durham sandy loam with slopes ranging from 3 to 6 percent. Each 

 plot was 16 feet wide. This allowed four tobacco rows, run lengthwise 

 of the plot, with the center row middle on the designated grade. To- 

 bacco was planted each year following a winter cover of rye or rye- 

 grass. Cultural practices were similar to those usually followed by 

 tobacco farmers of the area. Equipment was installed to measure both 

 runoff and soil loss after each rain. 



Supplementary velocity tests were also conducted while the row- 

 grade experiment was in progress. One cubic foot of water per minute 

 was run into the upper ends of the rows for a period of 30 minutes and 

 the velocity measured. Results of the experiment, including runoff, 

 velocity, and soil loss, are shown in figure 7. 



Runoff almost doubled when the grade was increased from to 6 

 inches per 100 feet. There was a further slight increase in runoff 

 when the grade was increased to 12 inches. Increases in row grades 

 above 12 inches, however, caused no significant increases in runoff. 

 This means that runoff, or drainage, was adequate with as little as 

 6 to 12 inches fall per 100 feet. It means also that steeper grades, 

 such as are frequently seen in many tobacco fields, are unnecessary for 

 effective roAv drainage. 



Soil loss, on the other hand, tended to increase rapidly with the 

 grade and reached serious proportions with the 30-inch grade. Under 

 the conditions of this experiment, an increase of 12 inches, or 1 per- 

 cent, in row grade increased soil loss approximately 4 tons per acre. 

 If the row grades had been extended to 6 or 8 percent, as is the case 

 in many tobacco fields, it is obvious that the soil loss would have been 

 tremendously increased. 



Velocity of runoff water likewise increased with the grade and it 

 may be seen in figure 8 that with the 30-inch grade the water was 

 flowing about twice as fast as in the row with 6-inch grade. Appar- 

 ently, this increase in velocity caused the increase in soil loss as total 

 runoff was not greatly increased between the 6-inch and 30-inch grades. 



The amount of row grade was usually indicated by the appearance 

 of the row middles following rains. Rows on the contour and with 

 6-inch grade showed little evidence of velocity and soil movement. 



