QUESTIONS 185 



Illustration Material for Lessons. Show nodules on the roots of some of 

 the common legumes. 



Demonstrations. Material Needed. Five one-gallon crocks; about 12 

 quarts of loam; about 10 quarts of soil void of alfalfa nodule organisms; a few 

 corn and grain seeds; 2 grams each of nitrate of soda and sodium acid phos- 

 phate; a few hundred alfalfa seeds; and alfalfa inoculation soil or culture. 



To Study the Effect of too Much Water on Plant Growth in Relation 

 to Nitrification. Procedure. Plant 3 one-gallon crocks of sandy loam, or 

 loam taken from the field, to corn and small grain. Water them and keep 

 them under the same favorable growing conditions. To crock No. 1 apply 

 2 grams each of dissolved sodium nitrate and sodium acid phosphate (to enrich 

 the soil). When the plants are about 3 to 4 inches high, treat them as follows: 



Crock No. 1 Keep flooded with water. 



Crock No. 2 Keep flooded with water. 



Crock No. 3 Water normally. 



Start moisture treatments all at the same time. Continue these treat- 

 ments for at least 2 weeks, or until results are definite. 



Questions. (a) Why did the plants in crock No. 2 turn yellow so soon? 



(6) Explain the results secured in crock No. 1. 



(c) Define nitrification. 



(d) Name conditions in the field that favor nitrification. 



To Demonstrate the Importance of Inoculation. Procedure. Fill two 

 one-gallon crocks with soil free of alfalfa nodule organisms. Provide proper 

 conditions in each crock for growing ali'alfa. Inoculate one crock, but do not 

 inoculate the other. Seed both crocks to alfalfa, water, and observe results. 



Field Studies. Observe nodules on the roots of clovers and other legumes. 

 Do not pull roots but dig them, and rinse off the soil in water. 



Examine the roots of "yellow" alfalfa, and of vigorous plants for nodules. 



Home Experiment. It would be of interest as a home experiment to 

 plant two strips side by side of some legume not commonly grown in the com- 

 munity. One of the strips should be inoculated, and the other left uninocu- 

 lated. (Consult text.) Note results in nodule development and in yield. 



QUESTIONS 



1. Name the different classes of soil organisms. What are microorganisms? 



Tell of their number in soils. 



2. Into what three classes may the helpful soil organisms be grouped? 



3. What becomes of all dead organic material? Of what importance is 



this fact? 



4. How is it possible that the nitrogen in organic matter becomes available? 



5. From what main source does a crop like corn get its nitrogen? Its min- 



eral elements? 



6. Explain why the fertility of some light-colored soils rich in the mineral 



elements may be increased just by plowing under a crop of green rye. 



7. Upon what depends the value of an organic fertilizer, like dried blood? 



Of some insoluble mineral fertilizer, like rock phosphate? 



8. Explain by aid of a diagram how plants are able to secure nitrogen from 



the organic matter in soils. What is the meaning of nitrification? 



9. What becomes of the nitrates formed as the result of nitrification? 



10. What do "catch crops" catch? Why are some crops called "cover" crops? 



11. Does the process of nitrification increase the nitrogen content of 



soils? Explain. 



12. What is meant by denitrification? 



13. How may the beneficial effect of manure on peat and muck soils be 



partly explained? 



