108 SOIL WATER AND ITS RELATION TO SOIL FERTILITY 



9. Is moisture ever a limiting factor in production in humid farming? Explain. 



10. What is the problem that confronts the dry-land farmer? What is the 



problem concerning the water supply in humid farming? 



11. Name and define the three forms of soil water. Which is of most import- 



ance in crop production? 



12. How do soils hold capillary water? When can a soil hold its greatest 



amount of capillary water? 



13. Compare a coarse sand with a fine sand in the amount of water it can hold 



for crop use. 



14. Why can a black silt loam hold a large amount of capillary water? 



15. What is percolation? 



16. What is the relation between percolation and soil erosion? 



17. What is the importance of percolation in land drainage? What facilitates 



percolation under field conditions? 



18. What is seepage? Illustrate. 



19. What is meant by capillary rise of soil moisture? Give other illustrations 



of this phenomenon. How does capillary water rise in soils? 



20. Name and discuss three factors influencing capillary rise of soil water 



which farmers should consider. 



21. What is meant by water-holding capacity of a soil? How do soils vary 



in this capacity? 



22. What forms of soil moisture does "water-holding capacity" include? Can 



plants use all the water indicated by* 'water-holding capacity"? Explain. 



23. Compare the available moisture supply a light-colored silt loam can hold 



with that of a coarse sand. 



24. What are "drouthy" soils? What is an important point to consider with 



respect to subsoil in buying a farm? 



25. Mention ways in which water from rainfall may be lost to the crops. 



26. Name ways in which moisture may be conserved and controlled. 



27. How may surface run-off be lessened? 



28. How may the water-holding capacity of soils be increased? 



29. How can a farmer aid capillary rise of soil moisture? Why is it best not 



to subsoil land having sand as subsoil? 



30. What is a soil mulch? Under what conditions can it be maintained? 



31. What constitutes a good soil mulch in humid farming? In dry-land 



farming? 



32. Explain by use of a diagram how a soil mulch conserves moisture. How 



may a soil mulch be maintained? 



33. When is a soil mulch of greatest value? How does a soil mulch aid 



cultivation? 



34. What are self -forming mulches and "protective crusts"? 



35. Explain the uses of straw and other materials used as mulches. 



36. What bearing have weeds on moisture conservation? 



PROBLEMS 



1. A barrel of water weighs 263 pounds and an acre of water one inch 

 deep weighs 113 tons. How many inches of water are required to grow a 

 50-bushel oat crop? A 2-ton clover crop? A 5-ton alfalfa crop? 



2. If on a certain farm % of the rainfall during the growing period is 

 used by the crops, & is lost by percolation, % lost as surface run-off and % 

 the amount used by the crops is lost through evaporation from the soil, how 

 many inches of rainfall would be required to grow the crops in problem 1? 



3. What per cent more water is used by the clover plant in a semi-arid 

 than in a humid climate? Assuming this would apply to alfalfa, about what 

 would be the water requirement of alfalfa in a humid climate? 



