7. HOW TO KEEP THE SOIL FERTILE. 



Illustrative material: Two jars or dishes, rain water, well water, 

 two small pieces of gauze, and a few kernels of wheat. A small 

 sample each of nitrate of soda (Chile saltpeter), phosphoric acid, 

 and caustic potash, illustrating common forms in which these sub- 

 stances are used by plants. These substances may be purchased at 

 a drug store. 



How to Make the Land Poor. If we dissolve an ounce 

 of sugar in a glass of water, and then dip out a teaspoon- 

 ful of the solution, of course we take out a part of the 

 sugar. We learned in Lesson 4 that plants take up soil 

 water containing dissolved mineral matters. Now, if 

 these plants are taken off the land on which they are 

 growing, the soil can not contain so much soluble mineral 

 matter as it contained before. If we continue to raise 

 crops on the land, and to take them off and sell them 

 without returning any soluble mineral matter to the soil, 

 the soil will soon become " poor," that is, there will 

 not remain enough of some mineral matters to feed plants 

 well. 



Certain Food Required by Plants. When a painter 

 wishes to prepare some paint to match a particular shade 

 of color, he mixes a certain amount of paint of two or 

 more colors; if he uses a larger or a smaller quantity 

 of one of these colors, or if he adds another color he does 

 not get the tint he desires. It is just so when Mother 

 Nature builds up a wheat plant ; she uses certain amounts 

 of a definite number of materials from the soil, and can 



G. & M. Ag. 3. ^ 



