CHAPTER XXII 

 COMMERCIAL FEBTILIZEB MATERIALS^ 



While the use of animal excrement on cultivated soils was 

 practiced as far back as systematic agriculture can definitely 

 be traced, tlie earliest record of tbe use of mineral salts for in- 

 creasing the yield of crops was published in 1669 by Sir 

 Kenelm Digby.^ He says: ''By the help of plain salt petre, 

 diluted in water, and mingled with some other fit earthly 

 substance, that may familiarize it a little with the corn into 

 which I endeavored to introduce it, I have made the barrenest 

 ground far outgo the richest in giving a prodigiously plentiful 

 harvest." His dissertation does not however, show any true 

 conception of the reason for the increase in the crop through 

 the use of this fertilizer. In fact, the lack of any real knowl- 

 edge at that time of the composition of the plant would have 

 made this impossible. 



In 1804, de Saussure,^ a Frenchman, called attention, for 

 the first time to the significance of the ash ingredients of 

 plants not only showing that these mineral materials were 



^The following general references may prove helpful: 



Hall, A. D., Fertilisers and Manure; New York, 1921, 



Halligan, J. E., Soil Fertility and Fertihcers; Easton, Pa., 1912. 



Van Slyke, L. L., Fertilisers and Crops; New York, 1912. 



Fraps, Gr. S., Frinciples of Agricultural Chemistry; Easton, Pa., 

 1912, 



Collins, S. H., Chemical Fertilisers and Parasiticides; New York, 

 1920. 



^Digby, Kenelm, A Discourse Concerning the Vegetation of Plants; 

 London, 1669. 



^ Saussiire, Theodore de, JKecherclies Chimiques sur la Vegetation; 

 Paris, 1804. 



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