78 
BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
another portion produced 15.8 tons per acre. The rock phosphate cost $10 per ton 
and the potash fertilizer $46. How many more dollars' worth of plant food in the 
manure did it require to produce the gain in yield for that year? 
7. A mixture of acid phosphate and muriate of potash in the proportion of 100 pounds 
to 60 pounds, respectively, was applied to a field at the rate of 150 pounds per acre. The 
field produced 14.5 tons of silage corn per acre as compared with 3 tons where no treat- 
ment was made. The acid phosphate cost this farmer $16 per ton, and the potash 
fertilizer $45 per ton. What was the cost of this fertilizer treatment, and what may 
be considered the interest on the fertilizer investment for that year? 
A farmer owns a clay farm of 160 acres. For regular cropping purposes he has six 
20-acre fields. His crops are alfalfa, corn (two fields each year), oats, wheat, and red 
clover. The alfalfa occupies a field for five years, then is plowed for corn. The crops 
on the other fields are, in the order named, corn, oats, wheat, red clover. Rye, or rye 
and vetch, are used as a cover crop following the crops of corn. The crops are so 
planned in the five fields not growing alfalfa that each year the farmer has two fields 
of corn and one field each of oats, wheat, and clover. The analysis of the soil on this 
farm is fairly uniform and shows per acre in the total 8 inches of surface 4,000 pounds 
of nitrogen, 2,000 pounds of phosphorus, and 24,000 pounds of total potassium. 
8. If C stand for corn, O for oats, W for wheat, and CL for red clover, and A for 
alfalfa, fill in the blank below so that the order of cropping in each field will be as given 
above, and so that there will be for harvest each year one field of alfalfa, two of corn, 
and one each of oats, wheat, and clover. 
Field. 
Year. 
1 
2 
3 
4 
5 
fi 
1 
A 
2 
A 
3 
A 
4 
A 
. 
5 
A 
| 
9. Assuming that the plant food liberated from this soil during the average season 
is equivalent to 2 per cent of the total nitrogen, 1 per cent of the phosphorus and J of 
1 per cent of the potassium : 
(a) From table 23, reference No. 5, page 154, determine whether sufficient of the 
plant-food elements, nitrogen, phosphorus, and potassium, would be liberated during 
a growing season on this farm to produce a 100-bushel crop of corn. 
(b) Compute whether any of these plant-food elements is present in this soil in 
sufficient quantity to produce the maximum of any crop noted in table 23. 
] 0. The yields of crops on the farm averages 4 tons of alfalfa hay per acre, 50 bushels 
of corn per acre with 2 tons of stover, 50 bushels of oats with 1| tons of straw, 25 
bushels of wheat with 1| tons of straw, and 3 bushels of clover seed per acre with 
1^ tons of clover hay the first cutting, three-fourths tons clover straw from hulling, 
and one-half ton growth of clover to turn under for corn. 
(a) If the farmer sells his alfalfa, the grain including the corn, and the clover seed, 
but returns to the soil all corn stover, straw, and clover; and if each ton of clover 
fixes in its growth 40 pounds of nitrogen, and each clover crop fixes 12 pounds of 
