132 PRACTICAL FARM CHEMISTRY. 



perhaps nitrogen. The fertility of the soil is grad- 

 ually increased, but it will be somewhat one-sided, 

 since the supply of phosphoric acid receives no ad- 

 dition except what the soil itself may furnish in 

 consequence of natural chemical disintegration. 

 Probably there are few farmers that raise cereals 

 thus persistently, and manure thus liberally. 



A yearly application of four tons of ordinary 

 mixed stable manure to the acre would replace all 

 the potash and, when we add the amount furnished 

 by the atmosphere, nearly all the nitrogen that the 

 grain crops have taken off. The only important 

 substance not returned in full is phosphoric acid, 

 which is taken off regularly so that the natural 

 supply must be gradually lowered. We will at last 

 come to a stage where its want must be felt. This 

 is the exact condition of thousands of grain farms 

 east, west, and south. 



Here we have made one soil diagnosis, based 

 merely upon our knowledge of the treatment which 

 a certain soil has received during a period of a num- 

 ber of years. We have come to the conclusion that 

 it lacks phosphoric acid. This we must supply in 

 order to restore the proper balance of 



Where PhoB- the plant foods contained in it. The 

 ^Needed" cheapest way to do this is by the use 

 of a simple phosphate or superphos^ 

 phate. Among the substances suitable for this pur- 

 pose, we have bone, bone charcoal, and dissolved 

 bone black, phosphatic guano, basic slag, South 

 Carolina floats and dissolved rock. In some cases 

 especially where the soil is up to our standard of 

 fertility, and time can be allowed for making the 

 phosphoric acid soluble, floats may answer, and will 

 be cheapest. In the majority of cases it will be 



