298 - THE PRINCIPLES OF AGRICULTURE 



Why is soil moisture important in agricultural practice? How 

 do plants use water? How may the loss of water from the plant 

 be shown? What is irrigation? Under what conditions is irriga- 

 tion admissible (63a)? In what part of the country is it a gen- 

 eral practice, and in what part a special practice? 



In what forms may water be held in the soil? Explain each of 

 these three methods (65, 66, 67). Make an experiment to show 

 the capillary power of the soil. What is meant by the term "film 

 moisture?" In what condition is the water held in very wet soils? 

 When lands are in proper condition for the growing of crops, is 

 the soil wet or is it moist? Illustrate film moisture by dipping a 

 marble or a stone in water. Illustrate capillarity by applying 

 one corner of a lump of sugar to water. Illustrate the transfer of 

 water from particle to particle by placing several lumps of sugar 

 together and applying water to one of them. Where is the free 

 water of the soil? What is meant by a "leachy" soil? In what 

 soils and under what conditions does water run off the surfo.ee? 

 Does this wash of water from the surface do any harm aside from 

 the loss of the water itself? 



What is meant by the term "rainfall?" How may the soil be 

 made to hold the rainfall? How may surface washing be pre- 

 vented? How do soils vary in their capacity to hold water? 

 Make an experiment to illustrate the capacity of the different 

 soils to hold moisture (72o). How does the humus content of the 

 soil affect its moisture-holding capacity? How important is 

 humus in the agriculture of your region? Is there sufficient rain- 

 fall in this region to carry the crops through the season without 

 resorting to irrigation? 



How is the humus in the soil depleted? State one reason why 

 newly broken or newly cleared lands give the best crops. How 

 may the humus be gradually increased? Is it possible to put too 

 much humus in the land? The pupil should be instructed in the 

 effect of humus in different kinds of soils. Soils that are already 

 rich in humus may be injured rather than benefited by the appli- 

 cation of more, whereas those that are lacking in humus or are 

 very hard, or very loose and sandy, maybe greatly benefited. In 

 many of the loess soils of the middle West the addition of much 



