46 BULLETIN 355, V. S. DEPAETMENT OF AGEICULTURE. 



acre, 25 acres of oats averaging 40 bushels per acre, and 50 acres of com yielding 52 

 bushels of shelled corn per acre? 



2. A clay or silt loam soil weighs in round numbers 2,000,000 pounds per acre, 8 

 inches deep. How many pounds of nitrogen are contained in an acre 8 inches deep 

 of a fertile clay loaon that analyzes 0.25 per cent of nitrogen? (a) How many 65- 

 bushel com crops will the nitrogen contained in an acre of this soil supply? 



3. An acre of sand 8 inches deep weighs, in round numbers, 2,500,000 poimds. 

 What is the nitrogen content of an acre of poor sand that analyzes 0.04 per cent nitrogen? 



4. An acre of peat soil 8 inches deep weighs, in round numbers, 350,000 pounds. 

 How many pounds of nitrogen are contained in an acre 8 inches deep of a soil of this 

 kind that analyzes 2i per cent nitrogen? 



5. A certain silt loam contains 0.2 per cent nitrogen and a peat 3 per cent. In 

 comparing these percentages, how may times more nitrogen are contained in the peat 

 than in the silt loam? 



(a) In comparing the actual number of pounds per acre 8 inches, how many times 

 more nitrogen does the peat contain than the silt loam? T\Tiy this difference? 



6. One ton of red-clover hay contains about 40 pounds of nitrogen, and 1 ton of alfalfa 

 hay contains about 50 poimds. How many pounds of nitrogen are contained in 30 

 acres of clover yielding 2 tons per acre and 20 acre.s of alfalfa averaging 5^ tons per 

 acre from three cuttings? 



(a) How many pounds of nitrogen can reasonably be assumed to have been fixed 

 from the air by these two crops? 



(b) At 15 cents per pound what is the value of the nitrogen contained in 5 tons of 

 alfalfa hay? 



(c) Wheat bran contains 2.5 per cent nitrogen. How much bran is equivalent to 

 1 ton of alfalfa in nitrogen content? 



7. How many square inches of air over 1 acre? 



8. Atmospheric pressure averages about 15 pounds per square inch. How many 

 tons of air over 1 acre? 



9. About four-fifths of the atmosphere consists of nitrogen. How many tons of 

 nitrogen over 1 acre? Do you think legumes will ever run short of this element in 

 their work of nitrogen fixation? 



REVIEW QUESTIONS, LESSON VI. 



1. Discuss fully the fixation of nitrogen in the soil by nodule bacteria. 



2. Name some leguminous plants. In what particulars, from the standpoint of 

 soil fertility, do they differ from non leguminous plants? 



3. Explain what is meant by inoculation of soils. 



4. "WTiat conditions affect the amount of nitrogen fixed by legumes? 



5. About how much nitrogen is fixed by a 2-ton clover crop? 



6. Explain fully how legumes may be made of most use in increasing the amount of 

 nitrogen in the soil of a farm. 



7. "\ATiat is meant by nitrification, and how does it differ from nitrogen fixation? 



8. Name some of the commercial materials used to increase the nitrogen content of 

 the soil. 



9. Compare the value of these commercial materials with the products of vegetable 

 decay in general farm practice. 



10. Is all vegetable matter in soils helpful in supplying fertility? Explain. 



11. May soils be considerd inexhaustible in fertility? 



12. Explain fully why a given soil may produce a large growth of native vegetation 

 while the same soil after being brought under cultivation may-fail to produce a large 

 yield if the crops are removed from the land each year. 



