(^4) EXERCISE 20 (Continued) 



6. When air is admitted to the soil in very early spring, what effect does it 



have upon the soil temperature? Explain. 



7. In early spring is it better to allow the surplus water to percolate downward 



into the soil or to wait for it to evaporate from the surface? Give reasons 



8. If free water is caused to percolate below the depth of tillage in spring' 



what benefit may it have upon crops during subsequent dry weather? ' 



