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



The Maryland Area 



1. Tobacco, small grain followed by grass and lespedeza or clover. 

 This is used as a 3- or 4-year rotation. 



2. Tobacco every other year followed by a winter cover of vetch and 

 small grain which is permitted to mature and fall on the ground dur- 

 ing the summer. 



3. Tobacco every year with a winter cover of small grain, or small 

 grain-vetch mixtures. 



Rotations as followed on tobacco land have developed largely as a 

 result of farm practice and have not been based, to any great extent, 

 on experimental data. They are relatively weak from the standpoint 

 of soil protection and from the economic returns from the other crops 

 grown in the rotation with tobacco. In many cases they do not make 

 adequate contribution to the yield and quality of the tobacco. 



The proper use of rotations on tobacco land is an unsolved problem. 

 The serious nature and extent of erosion on these lands justifies fur- 

 ther concerted research efforts to develop crop rotations which give 

 maximum protection to the soil and additional income while safe- 

 guarding the tobacco crop quality. Important considerations in- 

 clude : 



1. Sod crops, the residual effects of which greatly increase the re- 

 sistance of soil to erosion. 



2. Crop sequences which maintain high quality in the tobacco crop. 



3. Management of crop residues to control nitrogen release during 

 the tobacco year. 



4. Crop plants that will yield satisfactory profits when grown on 

 tobacco soil. 



WINTER COVER CROPS AND EROSION LOSSES 



Winter cover crops have been generally recommended for winter 

 protection and as a source of organic material for soil improvement. 

 They are known to reduce erosion on many soil types, particularly on 

 the heavier types (^, 5). In studies at Statesville on Cecil sandy clay 

 loam they reduced erosion to less than one-half that where none was 

 turned under. 



At the Raleigh station the effect of winter covers was studied on 

 the sandier soils under tobacco culture. Rye and ryegrass seeded 

 as winter covers with and without additional nitrogen at seeding time, 

 were compared with no winter cover. All plots were laid out so as 

 to have a row grade of 18 inches per 100 feet and ridge cultivation 

 was followed. 



Soil loss measurements over a 4-year period showed an annual de- 

 crease in soil loss of 6 percent for ryegrass and 14 percent for rye, when 

 compared with that from tobacco following no winter cover. Adding 

 24 pounds of nitrogen per acre at seeding increased these effects to 48 

 percent for ryegrass and 18 percent for rye. 



If these cover-crop and residue effects are considered on a seasonal 

 basis the benefits are much better understood. Seasonal soil losses 

 from rye, nitrated rye, and no cover are shown in figure 24. First it 

 was found that there was very little erosion during the winter months, 

 from November through March, either with or without winter cover. 



