20 LAND DRAINAGE 



On such soils, except when a sod is to be turned down, the 

 disk harrow is to be preferred to the plow, when the plant- 

 ing must be done at once. The same discussion may 

 apply to very sandy soils also. 



27. Structure and germination. On clay soils or 

 heavy loams, a severe rain, just after the seed has been 

 planted, will frequently so pack the soil that many of the 

 seeds will fail to germinate, or the germination may be 

 greatly delayed. Of the seeds that germinate, many will 

 fail to thrust the parts out of the ground, and many others 

 will be greatly delayed. 



Seeds planted in over-loose or in over-lumpy soil may 

 fail to germinate, or may be so delayed that at harvest 

 time some plants will have ripened their seed, while others 

 will have brought them only to the milk stage, or even 

 to the flowering stage. (See Fig. 20.) Obviously soil 

 structure plays an important part in germination. 



28. Structure and root development. Mention has 

 already been made of the extent of the development of 

 the root systems of our domestic plants, and of the need 

 of the plant for such root development to secure both 

 food and moisture. The tender tips of the developing 

 rootlets can penetrate a hard or compact soil but slowly, 

 and, therefore, for but relatively short distances. The 

 root system developed under such conditions will be 

 marked by short roots and fewer of them. Therefore 

 the crop suffers. 



29. Root development restricted by fissuring. In a 

 soil (or subsoil) checked by large fissures or cracks, a 

 root may advance to the fissure and grow out into it, 

 but will find difficulty in making an entrance into the 

 opposite wall, especially if the soil of the opposite wall 

 is hard as is almost sure to be the case where large cleavages 



