FERTILIZERS. 55 



out phosphate were nearly as tall as those with a complete fertilizer, 

 but were slender and the seeds were deficient in weight ; without 

 potash the same as without phosphate ; while without nitrogen, the 

 growth was almost nothing, showing that this soil lacked available 

 phosphoric acid and potash, and, most of all, nitrogen. Some soils 

 will grow almost anything that is planted on them ; such soils pos- 

 sess all the ingredients of plant food. 



Prof. Atwater said that he had received hundreds of letters, of 

 which the burden was, What shall I put on my soils to produce crops ? 

 If all soils were alike in their ways of supplying crops with food, 

 and all crops alike in their ways of using it, the answers to such 

 questions would be eas}" ; as it is, it is impossible to lay down rules 

 to cover all cases. 



The chief value of fertilizers is their plant food. The main use 

 of guanos, phosphates, bone, fish, potash, salts, and the like, is to 

 sui)ply the crops witli food which they cannot get enough of from 

 the soil. The rule in buying them should be to select those wliich 

 supply in the best forms and at the lowest cost, tlie i)laut food 

 which the crops need and the soils fail to furnish. 



We may take it as pretty well settled that the only ingredients of 

 plant food which we need supply to our soils, are potash, Ume, 

 magnesia, 2:)hosphoric acid, sulpJmric acid, and nitrogen. Iron 

 and chlorine are necessary to the perfect growth of plants, but only 

 in minute quantities. Silica and soda are needed, if at all, in simi- 

 larl}' small proportions. Every ordinar}' soil supplies these last 

 four substances in abundance. 



Of the above list, the magnesia is rarel}' deficient in even " worn- 

 out" soils. Sulphuric acid and lime are more often lacking, and 

 hence, doubtless, one reason of the good effect so often observed 

 from the application of lime and plaster. The remaining substances, 

 phosphoric acid, nitiogen, and potash, are the most apt to be 

 deficient. In some soils one, in others several or all, of these may 

 be wanting. When we say the ingredients are " wanting," we do 

 not mean that the soil does not contain them, but that it does not 

 supply the crops as much as the}' need. It is not so much because 

 our " worn-out " soils have not enough plant food in store that 

 crops starve upon them, but rather because the food is locked up in 

 such combinations that the roots can not get at and use them. 

 Such is the general result of the best testimony that experience 

 and experiment have placed at our disposal. 



