392 Agricultural Bacteriology. 



mation of nitrates are the ones that are naturally de- 

 manded by the green plant in normal growth. 



Some of the soil bacteria derive their supply of nitro- 

 gen from, the same source as do the green plants, i. e., 

 the nitrates. If these forms are abundant in the soil, 

 they will compete with the plants for the nitrate present. 

 Since, as has been indicated, the nitrogen is most often 

 the limiting factor in plant growth, it is important that 

 as much of it be reserved for the crop as possible. The 

 presence of weeds in the field may limit the crop because 

 they use a portion of the nitrogen that would otherwise 

 be available for the crop. The bacteria that use the ni- 

 trogen of nitrates may limit the crop in the same manner. 

 The conditions that favor their action and their import- 

 ance in the soil are problems yet unsolved. 



During the decomposition of organic matter of all 

 kinds some of the nitrogen is set free. It is not known 

 that the farmer can prevent this in the soil, but in the 

 handling of the most important by-product of the farm, 

 the manure, much can be done to avoid this loss. 



Conservation of nitrogen. It is desirable to conserve 

 the supply of nitrogen in the soil as much as possible 

 since to restore the nitrogen supply is a slow process 

 when the natural factors are relied on, while to furnish 

 the amounl needed by a crop in the form of commercial 

 fertilizers would be too expensive. 



During the growing season nitrates are being con- 

 stantly formed and are as rapidly used by the crop. In 

 the more fertile soils a greater amount of nitrate may be 

 formed than is needed by the plant. Some of this is 

 taken up by the plant but it not used. It accumulates 

 in the tissues as potassium nitrate. It has been thought 

 by some that the corn stalk disease previously described 



