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MISC. PUBLICATION 65 6, U. S. DEPT. OF AGRICULTURE 



quickly reverse and drain in the opposite direction where the area 

 between terraces begins to widen. 



2. When laid out parallel with the lower terrace, rows in widening 

 sections will drain toward the outlet but will reverse and run in 

 the opposite direction in narrowing sections. In either case there 

 is a characteristic failure of crop rows to drain properly when laid 

 out parallel to either terrace. This failure of tobacco rows to carry 

 off their own water results in ponding and row breakage during heavy 

 summer rainstorms (fig. 13. A). In case of ponding, the tobacco 

 plants may be severely damaged by drowning (fig. 13. B). Serious 

 breaks across the rows cause heavy soil loss, silting of terraces and 

 waterways, and frequent breakage in the terrace below. 



IMPROVED ROW SYSTEM 



The best erosion-control measure for land in tobacco is a good row 

 lay-out in which the rows act as miniature terraces and drain all the 

 way through to the outlet with a moderate but continuous grade. 



An improved method for obtaining this row lay-out has been de- 

 veloped by the Soil Conservation Service and is commonly designated 

 the "string method." This method takes advantage of the effect of 

 change of slope on grade of row as illustrated in figure 12. It corrects 

 the faults of conventional methods and provides continuous row drain- 

 age throughout the terrace interval (the land area between terraces). 



Guide-row changes with change in width between terraces: 



(1) When narrowing, (2) When widening, 



follow upper terrace follow lower terrace 



Guide row: Begins -*, direction of slope > 

 Guide-row control'changes 

 ~ Crop rows 



Figure 14. — A terrace interval, showing the guide row laid out by the ''string 

 method." Beginning at the higher end, the interval between the terraces first 

 narrows and then widens as it approaches the outlet (right side of diagram). 

 Note that in the narrowing section the guide row parallels the upper terrace 

 and that it parallels the lower terrace in the widening section. 



