326 ELEMENTS OF FARM PRACTICE 



table matter added by grain crops, and by grass crops, by 

 pulling a few of the stubbles of grain and of clover and 

 timothy. One will find that the grain stubble is pulled up 

 very easily and that some digging must be done to get 

 stubble of any of the grass plants. 



In the simple three-year rotation, corn, grain and clover, 

 discussed on page 320 you will see that each field will be 

 in clover once every three years. This will add sufficient 

 vegetable matter to keep the soil reasonably well supplied 

 during the other two years while the corn and grain crops, 

 or crops that exhaust the vegetable matter, are growing. 



Cultivated crops, as corn, probably return as much 

 vegetable matter to the soil in the roots and stubble as do 

 the grain crops, but they use during their growth a great 

 deal more than the grain crops, on account of the cultiva- 

 tion given them. We have learned that moisture and air 

 are essential to decomposition. By the cultivation of these 

 crops the soil is loosened on top, so that air can enter freely 

 and so that moisture does not rise to the surface to evaporate, 

 as it rises in a grain field that is not cultivated while the 

 crop is growing. Thus the two essentials to decomposition, 

 air and moisture, are maintained. Consequently decomposi- 

 tion is more rapid and more of the vegetable matter is 

 decomposed. 



A rotation which provides for growing grass on one 

 third of the tillable land furnishes a great deal of pasture 

 and hay, which usually is an incentive to keep more 

 live stock. Hence more manure is produced than is usually 

 available on a grain farm. More manure can be apphed 

 to the fields; and this, too, has a marked effect in keeping 

 up the supply of vegetable matter. 

 Questions: 



1. What is generally lacking when a soil ceases to be productive? 



2. In what ways does the rotation of crops tend to increase the 

 supply of vegetable matter in the soil? 



3. How can you prove that grass crops add more vegetable 

 matter to the soil than grain crops? 



Arithmetic: 



1. It costs $13.04 per acre to grow a crop of oats. How much 

 will it cost to grow 33 J^ acres of oats? 



• 2. It costs $16.20 per acre to grow a crop of corn. How much 

 will it cost to grow 333^ acres of corn? 



