REVIEW OF THE BOOK 299 



humus may be a decided disadvantage. Call attention to the fact 

 that in very windy regions the soil may be made so loose and 

 open and fine as to be exposed to much damage by winds. In 

 new countries humus may be more abundant than in old lands: 

 why? Are the lands in your neighborhood in need of humus? 

 Illustrate when green-crops should be plowed under for the pur- 

 pose of giving the best results. What is the danger of plowing 

 them under too late in the season (74^f 



Explain what drainage is. What is surface drainage and 

 under-drainape? How may surface drains be constructed so as 

 to interfere least with agricultural operations? What effect has 

 tinder-drainage on the soil? What effect does a warm shower in 

 spring have on land that is perfectly drained? What effect does 

 a cool summer shower have? Explain some of the practices of 

 tile draining, as to depth of drain, distance apart of the different 

 drains (76a, 76b). What relation does under-drainage have to 

 tap-rooted plants (78)? What is meant by the "soil reservoir?" 



How does tillage enable the soil to hold moisture? How does 

 increasing the capillarity increase the moisture-holding capacity? 

 What is the general direction of the movement of moisture by 

 means of capillary attraction? May soil be made too fine? What 

 is meant by "puddling" of soils? 



What is meant by the "conservation of moisture?" How does 

 moisture escape from the land? What is meant by the "surface 

 mulch" or the "soil-mulch?" About how much water is required 

 to produce a pound of dry matter (81ft)? How does tillage save 

 the moisture? 



Explain fl) the general direction of movement of soil water 

 in the growing season; (2) how the moisture-holding capacity of 

 the soil may be increased; (3) how surface evaporation may be 

 lessened. 



Chapter 4 



The tillage of the soil may now be con- 

 sidered, for we have learned how important 

 the physical condition of the soil is, and also 



