42 



VERTICAL FA K M I X G 



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breaking down compounds containing this element and thrive 

 best in places that are not well ventilated. The first named 



form includes the beneficial 

 forms of soil organisms, while 

 those of the second class are 

 usually harmful. The very 

 cultivation and aeration of the 

 soil, therefore, promotes the 

 growth of the beneficial forms 

 and checks the activities of the 

 harmful ones. The deeper the 

 soil is loose and well aerated, 

 the deeper the helpful forms 

 are found. 



DIFFERENT FORMS or BACTERIA Harmful Bacteria. Some 

 (GREATLY ENLARGED) forms of bacteria produce de- 



structive diseases in the plants, 



both in the tops and branches and in the roots. The greatest 

 trouble from bacteria in the soil, however, comes from the 

 forms that attack .the nitrogen carrying foods and cause the 

 nitrogen to be unlocked from its combined form and to escape 

 as gas. These forms thrive best in wet and packed soil, 

 where they cause the organic substances to undergo a waste- 

 ful putrefaction rather than a beneficial decay. Their ac- 

 tivities are at once checked by the presence of free air. Some 

 crops grown continuously on the same soil for a long time 

 cause it to become filled with forms that cause diseases in the 

 roots. Generally these can be destroyed by a rotation of 

 crops attended with deep tillage. 



In short the control of harmful soil organism is accom- 

 plished by thorough drainage and good, deep cultivation. Many 

 of them seem to thrive best in sour soils which can be made 

 sweet and desirable for the beneficial forms by additions of lime. 



Beneficial Organisms. Bacterial action is beneficial to 

 agriculture in many ways. As soon as a plant or animal dies, 

 the influences that have restrained the action of the organisms 

 of decay are removed and the bacteria at once begin breaking 



