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 gram 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-gaUon crocks of sandy loam, or 

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

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

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

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



Crock No. 1 — ^Keep flooded with water. 



Crock No. 2 — ^Keep flooded mth water. 



Crock No. 3 — ^Water normally. 



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

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



QicesHons. — (a) Why did the plants m crock No. 2 turn yeUow so soon? 



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



(c) Defiine nitrification. 



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



To Demonstrate the Importance of Inoculation. — Procedure. — FiU two 

 one-gahon crocks with soil free of aKalfa nodule organisms. Provide proper 

 conchtions in each crock for growing alfalfa. 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 com 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 tmder 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? 



