

4 FUNDAMENTALS OF AGRICULTURE. 



Uses of Water to the Plant and Amount Required. 

 Besides these elements the plant throughout its 

 growth requires water. This water is used by the 

 plant in carrying into and through it the necessary 

 salts; in keeping the cell walls of the leaf tissue moist, 

 so as to allow them to absorb carbon dioxide from 

 the atmosphere, and in regulating the temperature of 

 the plant by evaporation of water from the leaf, just 

 as the temperature of the animal body is regulated by 

 the evaporation of the perspiration. The amount of 

 water used by crops varies greatly with the kind of 

 crop and with the climatic conditions, but is always 

 large. For instance in the growth of one pound of 

 dry matter of corn about 250 to 300 pounds of water 

 are used; for potatoes, 350 to 400; for clover, 500 to 

 600. 



EXERCISE. What is organic matter? What is inorganic matter? 

 What does a seedling live upon before roots are developed to take 

 food from the soil? Using the results in the Table, calculate the 

 amount of nitrogen, phosphoric acid and potash removed by forty 

 acres of potatoes yielding 250 bushels per acre. Compare the 

 amount in the previous question with that removed by 40 acres of 

 corn yielding 30 bushels per acre. Which of these two crops (corn 

 or potatoes) is the more exhausting on the soil? How many acre 

 inches of water will be necessary to produce 3 tons of clover hay? 



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SECTION III. SOIL FERTILITY. 



The Fertility of the Soil depends in part on the rate 

 at which the essential elements for plant growth be- 

 come available as a result of the chemical decompo- 

 sition of the rock particles and residue of former 

 plants of which the soil is composed. It also depends 

 on the amount and availability of moisture, and on the 

 tilth or physical condition of the soil with reference 

 to the readiness with which it can be penetrated by 

 the roots of growing crops. The decomposition of 

 the rock particles is, of course; very slow, and is largely 

 the result of the action of carbon dioxide in the soil 

 moisture, just as is the case in the forming of the soil 



