326 SOIL PHYSICS AND MANAGEMENT 



means is taken for mixing them with the soil they decompose 

 almost entirely, leaving little more than the ash of the plant to mix 

 with the soil. Even if this mixing were not necessary the vegetable 

 material would interfere with cultivation if left on the surface. 

 The plow is the best implement for covering all. organic material, 

 such as crop residues, weeds, and farmyard manure. 



3. Killing Weeds. A most important object of tillage is kill- 

 ing weeds. We see demonstrations everywhere of the fact that ordi- 

 nary crops amount to very little when in competition with weeds. 

 A weed is a better forager than a cultivated plant, and hence will 

 deprive it of both moisture and food, and it is necessary for suc- 

 cessful crop production that the weeds be destroyed. Tillage is the 

 best means so far devised for accomplishing this purpose. In some 

 cases, however, sprays have been used successfully, and if sprays 

 could be found which would not injure the crop, but would kill the 

 weeds, there is no question but that much of our tillage could be 

 dispensed with. 



4. Storing and Conserving Moisture. Plants require an 

 abundant supply of moisture for their germination and growth. In 

 nearly all climates through uneven distribution of rainfall the neces- 

 sity exists for storing moisture in the soil when it can be obtained 

 and for conserving this for the use of the crop later. The early 

 preparation of the soil by loosening and compacting slightly is the 

 best means for storing the supply of this for future use. Loosening 

 the soil allows rapid absorption with little run-off, while stirring 

 the surface soil later prevents any excessive loss through evapora- 

 tion. Of these two under ordinary humid conditions, the prepara- 

 tion of the soil for storing the moisture is of much more importance 

 than subsequent tillage for retaining it when a crop is growing. 

 Previous to the planting of the crop the soil should be kept stirred. 



5. Compacting the Soil. It frequently becomes necessary 

 after a soil has been plowed to compact it in order to close any 

 large air spaces that may exist in the plowed soil and also bring the 

 furrow-slice in close contact with the soil beneath it so that capillary 

 action may not be cut off. At the same time that the compacting 

 is done the soil should be pulverized, thus making a better seed bed 

 for the crop. 



6. Planting the Seed. While there is not much of what we 

 usually call tillage in the ordinary seeding of crops, yet all seeding 

 is accompanied by more or less working of the soil. 



