SELECTED BIBLIOGRAPHY 263 



7. A greenhouse bench filled with a loam soil is drenched with water. After 



drainage of water from below has ceased would you expect the water con- 

 tent of the soil to approximate most closely its moisture equivalent or its 

 water retaining capacity? 



8. For experimental purposes how would you keep the water content of the soil 



in a pot at approximately its moisture equivalent? 



9. A layer of soil is placed in the funnel of a filter pump, wet thoroughly 



and then subjected to maximum suction until no further drainage of water 

 occurs from the soil. Will the water content of the soil approximate most 

 closely the field capacity, water holding capacity, or the wilting percentage? 

 Explain. 



10. Dust mulches are often recommended as a means of conserving the water in 



the soil. Evaluate this practice. 



11. A corn plant, a young pine tree, and a fern were planted in equal-sized 



pots containing a silt loam, a sandy loam, and a clay loam, respectively, 

 and the pots sealed against water loss. The soil water was initially at 

 the moisture equivalent in each pot. Assume conditions were favorable to 

 a rather slow rate of transpiration. How will the Avater contents of the 

 soils compare at the wilting percentage? How will the diffusion pressure 

 deficits of the soil water compare? How will the amounts of water lost 

 from each soil before it reaches the wilting percentage compare? How 

 will the times required for the plants to reach permanent wilting compare? 



Suggested for Collateral Reading 



Keen, B. A. The physical properties of the soil. Longmans, Green and Co. 



London. 1931. 

 Robinson, G. W. Soils, their origin, constitution, and classification. D. Van 



Nostrand Co. New York. 1932. 

 Russell, E. J. Soil conditions and plant groivth. 7th Ed. Longmans, Green 



and Co. London. 1937. 

 U. S. Department of Agriculture. Soils and Men. Yearbook, 1938. 

 Waksman, S. A. Principles of soil microbiology. Williams and Wilklns Co. 



Baltimore. 1932. 

 Waksman, S. A. Humus. Williams and Wilkins Co. Baltimore. 1936. 



Selected Bibliography 



Briggs, L. J., and J. W. McLane. The moisture equivalent of soils. U. S. 



Bureau Soils Bull. No. 45. 1907. 

 Briggs, L. J., and H. L. Shantz. The ivilting coefficient for different plants 



and its indirect determination. U. S. Dept. Agric. Bur. Plant Ind. BulL 



No. 230. I9l2rt. 

 Briggs, L. J., and H. L. Shantz. The relative wilting coefficients for different 



plants. Bot. Gaz. 53: 229-235. 1912Z'. 

 Caldwell, J. S. The relation of environ/iirntal conditions to the phenomenon 



of permanent wilting in plants. Physiol. Res. i : 1-56. I9i3- 

 Gradmann, H. Untersuchungcn iiber die ff'asserverhdltnisse des Bodens als 



Grundlage des Pflanzenicachstums. Jahrb. Wiss. Bot. 69: I-IOO. 1928. 



