84 



PRODUCTIVE FARMING 



fertilizers, those that contain good forms of plant-food, 

 cannot be made from cheap materials, and if they contain 

 high percentages of the elements they cannot be sold for a 

 low price (Fig. 47). The price per ton, whether high or low, 

 is not a safe guide as to the effect that a fertihzer may have 

 upon the crop production. This is measured by the kind 

 and form of the materials used in the mixture. 



Exercise. — Dissolving Nitrate of Soda. — Put one-half 

 teaspoonful of nitrate of soda in a glass of water and stir 



Fig. 47. — The large square A represents a ton of low-grade fertilizer (for- 

 mula 2% nitrogen, 8% phosphoric acid, 2% potash). The valuable part is represented 

 by the dark square in the corner. The shaded area shows what is called filler, 

 which does no good to the soil. 



The large square B represents a ton of high-grade fertilizer. The valuable 

 part is what is shown by the white square in the comer. Some filler is always 

 present. It is represented by shaded area. 



until dissolved. Plants must have their food in the soil 

 dissolved before they can use it. Would this nitrate dissolve 

 in the rain? 



Exercise. — Collection of Fertilizers. — Let the pupils aid 

 the teacher in making a collection of all the different fertil- 

 izers to be found at the dealers or which can be secured by 

 mail. Put these in bottles with suitable labels. Keep them 

 for future study. 



Exercise. — Solubility of Phosphates. — Put a very little 

 phosphate rock which is ground fine in a glass of water 

 and see if it will dissolve. Do the same with a little ground 

 bone in another glass. Pour in a little clear lime-water. 

 If there were any phosphate dissolved this would cause a 



