62 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
(a) The nitrogen contained in the alfalfa crop may be considered the amount fixed 
from the air by that crop. How much nitrogen would be added to the soil if the 
manure produced from feeding 2 acres of alfalfa hay averaging 6 tons per acre were 
returned to the same field? Would there be a loss or gain of phosphorus, and how 
much? 
(6) A man fed 20 acres of corn yielding 65 bushels of shelled corn per acre, 10 acres 
of oats yielding 50 bushels, and 5 acres of alfalfa hay yielding 5 tons per acre. All 
manure produced was used on the farm. What was the loss or gain of nitrogen in the 
feeding transaction? 
(c) If 5 tons of cottonseed meal were fed during the time required to feed the 
crops in the preceding problem, what would be the loss or gain of nitrogen and phos- 
phorus to the soil? One ton of cottonseed meal contains about 135 pounds of nitrogen 
and 25 pounds of phosphorus. 
7. At the Hatch experiment station, Massachusetts, it was found that the drainage 
from the gutter behind milch cows contained 0.98 per cent nitrogen, 0.1 per cent 
phosphorus, and 0.73 per cent potassium. How many pounds of each of these ele- 
ments were contained in a ton of this liquid? 
(a) At the same station it was found that the liquid drained from a manure heap 
contained 1.5 per cent nitrogen, 0.043 per cent phosphorus, and 4.06 per cent potas- 
sium. Compare the fertility contained in 1 ton of this liquid with that in problem 7. 
What conclusions are to be drawn from these figures? 
REVIEW QUESTIONS, LESSON X. 
1. Name some of the factors which influence the amount of plant-food material 
that may be recovered in the manure produced from feeding. 
2. In what form is most of the nitrogen voided from the animal body? 
3. Compare the amount of phosphorus retained in milk with that retained in meat. 
4. About what part of the nitrogen and phosphorus in feeds fed is recovered in 
the manure? 
5. About what part of the plant food contained in feeds is returned to the soil? 
6. How may the loss of the liquid manure be reduced to a minimum? 
7. Explain how losses of plant food from manure occur. 
8. Discuss the time and method of applying manure. 
9. Discuss the condition manure should be in when applied to certain crops and 
soils. 
10. How much plant food is contained in 1 ton of average manure, and what is its 
value? 
11. What is a green manure? Under what conditions is it necessary to use -green 
manures to retain or to increase the fertility of a soil? 
12. What crops are best to use for green manuring? 
13. What is a cover crop? Of what value are cover crops to the soil besides their 
manurial value? 
14. What is a complete commercial fertilizer? 
15. Is it better to use fertilizers of high or low grade? Why? 
16. Discuss home mixing of fertilizers. 
LESSON IX. SOIL ACIDITY AND LIMING. 
(Ref. No. 1, pp. 242-248; or No. 5, pp. 160-164; or No. 6, pp. 313-319.) 
A condition of the soil which effects important ■ changes, including 
nitrification and nitrogen fixation, is that of acidity. Practically 
all soils formed in regions of moderately heavy rainfall and not 
