100 A YEAR IN AGRICULTURE 



Tillage opens up the soil to air and increases the water hold- 

 ing capacity. With the aeration of the soil, soil organisms 

 mentioned above flourish and successfully reproduce, and 

 these factors in turn render more plant-food available, thus 

 increasing the growth of the plant. It is a well known fact 

 that shallow cultivation prevents the escape of water by 

 evaporation and is, therefore, a successful method of water 

 conservation. Someone has said that weeds are a blessing 

 to the farmer because in the cultivation of the soil to rid the 

 land of weeds he brings about the results of cultivation men- 

 tioned above. Incidentally it may be noted that cultivation 

 of the soil is a method of combatting many insect pests. This 

 is especially true in the case of fall plowing, when the winter 

 stages of certain insects may thus be exposed to the freezing 

 weather. 



With the development of the science of physics and of 

 farm machinery, many new and efficient tools of cultivation 

 are coming to the farm to bring improvement in the culti- 

 vation of the soil. 



Soil organisms. In the discussion of physical conditions 

 of the soil we must not lose sight of the more recent dis- 

 coveries of the effects of soil organisms such as bacteria, 

 insects, worms, and even rodents upon soil conditions. It 

 has already been stated that the bacteria working in the 

 decaying organic matter of the soil make possible that con- 

 dition which we see in a rich, organic, loamy soil. Since these 

 soil organisms are so essential both to soil physics and soil 

 fertility, as we shall see later, it is necessary that the condi- 

 tions affecting their growth be kept favorable such condi- 



