ORGANIC CONSTITUENTS OF SOILS 157 



29. How much nitrogen is required for a 75-bushel crop of corn ? For a 



60-bushel crop of oats? For a 40-bushel crop of wheat? 



30. What are the evidences of nitrogen starvation? 



31. Of what value is organic matter in binding soil particles together? 



32. What part does erosion play in loss of organic matter? 



33. What are yellow " clay points "? 



34. What part does leaching play in loss of organic matter? 



35. Give an example of loss by fire. 



3(5. Is nitrification beneficial or detrimental to a soil? 



37. What are the objections to quicklime? 



38. What is meant by fallowing? Give the objects to be accomplished. 



39. What effect does it have on organic matter? 



40. What was the loss of organic matter due to forest fires? 



41. Where may fallowing be practiced economically? Why? 



42. What objection to ignition for determining organic matter of soils? 



43. Describe the dry combustion method. 



44. How may the carbon of soils be determined? 



45. Describe the method for determining the humus. 



46. If a soil contains 1.324 per cent of carbon, how many tons per acre of 



organic matter in the plowed soil? 



REFERENCES 



1 Hilgard, E. W., Soils, 1900, p. 130, quoting Kosticheff. 



'Schreiner, O., and Brown, B. E., Bulletin !)0, Bureau of Soils, 1912, Occur- 

 rence and Nature of Carbonized Material in Soils. 



' Hilgard, E. W., Soils, 190(5, pp. 13(5 and 137. 



*Snyder, Harry, Soils and Fertilizers, 1908, p. 105. 



8 Soil Reports, Illinois Station. 



"Unpublished data Soil Physics Division, University of Illinois. 



7 Snyder, Harrv, Soils and Fertilizers, 1908, p. 111. 



Hall, A. I)., The Soil, 1903, p. 109. 



Wiley, II. W., Principles and Practice of Agricultural Analvsis. 1900, vol. 

 i,*p. 337. 



"Op. Cit, p. 352. 



11 Briggs, I,. J., Martin, F. O., and Pearce, J. R., Bulletin 24, Bureau of 

 Soils, 1904, p. 34. 



11 Wiley, H. W., as above, p. 353. 



11 Bulletin 40, Bureau of Chemistry, U. S. I). A., p. 70. 



General Reference. Alway, F. J., and Bishop, E. S., Jour, of Agr. 

 Research, vol. v, No. 20, 1916. 



