12 FARM CROPS 



alike, and till with the same tools and the same 

 number of times, and under the same conditions. 

 To the first apply no fertilizer; to the second apply 

 all three elements; to the third apply nitrogen 

 only; to the fourth apply phosphorus only; to the 

 fifth apply potassium only. The results will show 

 whatever chemicals will pay on the land, and also 

 what elements are needed. 



STORING NITROGEN WITHOUT COST 



Of the three elements most likely to be removed 

 from the soil by continued crop production, nitrogen 

 is the most important, because, unlike phosphorus 

 and potassium, it is not found in appreciable quan- 

 tities in the original rock. Soil is decomposed rock, 

 therefore the decomposition and disintegration of 

 soils are continually supplying more potash and 

 more phosphoric acid, whereas nitrogen must be sup- 

 plied from some external source. The atmosphere is 

 composed very largely of nitrogen, and it has been 

 finally and definitely determined that one family 

 of plants, the leguminosae (clover, cowpeas), are 

 able, by the aid of certain micro-organisms in the 

 soil, to fix the free nitrogen of the air and to make 

 it available for the use of plants. 



The consideration of nitrogen in relation to soil 

 fertility is important also because of the properties 

 of this element. Of all the elements of plant 

 growth, nitrogen is the most fickle, unstable and 

 unreliable. It continually exhibits a tendency to 

 leave its chemical combination. For this reason it 

 is eminently fitted for the life processes which 

 require continued changes in the plant. But this 



