34 ELEMENTARY AGRICULTURE 



well. A sticky clay soil may be improved in texture, 

 and warmed up at the same time, by a plentiful addi- 

 tion of barnyard manure containing much straw. This 

 vegetable matter makes clay more like loam. The 

 same treatment is also good for sand, as it in- 

 creases the capacity of sand for holding moisture and 

 makes it like loam. If it were possible, and less ex- 

 pensive, many barren sandy places might be made fer- 

 tile by adding to them plentiful quantities of swamp 

 muck. This treatment would convert them into a loam 

 of good quality. Plowing under full grown crops 

 of rye or clover has much the same effect. Either 

 method adds humus to the soil and tends to make it 

 more loamy. Rye grows well on sandy soil, and clover 

 is a good crop to raise on clay for plowing under. A 

 good loam contains all the foods needed by growing 

 plants. 



Plant Foods that Become Exhausted. As has been 

 said before, only three of these foods, with the possible 

 addition of lime, ever become exhausted. You will 

 remember that these three are nitrogen, potash and 

 phosphoric acid. It is the purpose of the next chapter 

 to tell how you may judge from the character of the 

 soil, and the growing crop, which one of these plant 

 foods is most needed. 



Experimental Study of Soils. 



I. Rub a pinch of soil between the thumb and fore- 

 finger. Are its particles fine or coarse ? Spread a little 

 on the palm of the hand. Are the particles all of the 



