28 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 



COVERING THE SEED. 



In some cases the seed are covered by the drill itself. In others 

 the covering must be a separate operation. It is ordinarily accom- 

 plished by sifting sand or soil over the beds through a screen of 

 about one- fourth-inch mesh. One man can easily cover from forty to 

 fifty 4 by 12 foot beds per day of 8 hours. Skill is required to cover 

 the seed to a uniform depth so as to insure equable conditions and 

 relatively even germination. There is a tendency to distribute the 

 soil too deep over the center of the beds and too shallow along the 

 edges. One method of covering requires a frame and planing board 

 similar to those shown in figure 2. If broadcast sowing is prac- 

 ticed, the frame need not be removed from the time the bed is first 

 leveled until covering has been completed. The soil used in covering 

 is sifted over the seed bed, and a planing board, narrower by the 

 depth to which it is desired to cover the seed than the one used in 

 sowing, is then drawn along the frame. By this means the seed is 

 covered at a very even depth. Some other methods of covering are 

 followed. Soil is shaken off the blade of a shovel over the seed or 

 scattered by hand. In drill beds sown by hand the seed is sometimes 

 covered with the back of a rake or, as in one of the most successful 

 Forest Service nurseries, by drawing the finger through the soil 

 between the rows, thus closing the open drills. 



The depth of covering most suitable for any one species varies 

 according to differences in soil and nursery practice. Even under 

 very constant conditions some latitude may be exercised without 

 danger of seriously affecting the germination of the seed or their 

 subsequent pushing through the covering. If heavy clay soil is 

 used as a cover, the maximum depth permissible can not be so great 

 as if a lighter sandy soil is used because the seedlings experience 

 greater difficulty in breaking through. By reason of their greater 

 size and strength seedlings from large seed can more readily push 

 through a heavy covering than seedlings from small seed. There- 

 fore, the former can safely be covered more deeply than the latter. 

 • Less work is necessary to put on a light cover than a heavy one, 

 and the seedlings appear sooner and more evenly in the beds. It is 

 true that with a shallow covering there is greater probability of the 

 soil becoming dry to the depth of the seeds, resulting in damage 

 to them; but this possibility can not be avoided by any depth of 

 covering consistent with good nursery practice. Danger of this 

 nature must be guarded against by frequent watering or by pro- 

 tecting the seed beds. When moisture conditions in the seed beds 

 can be controlled, Forest Service experience indicates strongly that 

 shallow coverings are preferable, from one-eighth inch with smaller 

 classes of seed, such as spruce, the Thujas, larch, lodgepole pine, and 



