10 BULLETIN 757. U. S. DEPAKTMENT OF AGRICULTURE. 
and days when it is too wet for field work. This available time is 
distributed as follows : 
Days I Days. 
April 14 August 22 
May 22 ! September 20 
June 21 | October 22 
July 21 I November 2 
FACTORS THAT CONTROL COST OF PRODUCTION. 
Several important items enter into the cost of production of crops, 
each of which has a bearing on the profitableness of the various farm 
enterprises. In general, as each of these items increases in amount 
above a normal average the profit- decrease. There are. however, one 
or two exceptions, such as the cost of twiue and of thrashing, which 
are directly in proportion to the yield. 
USE OF LAND. 
The value of agricultural land, in general, is determined largely by 
its average productivity. Security of investment, profit- from ex- 
pected advances in value, and risk in production are other influenc- 
ing factors. The earning value or productive value of land in Xorth 
Dakota, however, is not always in proportion to its market value. 
The payment to capital for the use of the land in older farming 
communities is usually equivalent to the current rate of cash rent 
for such land, less taxes and upkeep of buildings. In Xorth Dakota 
scarcely any land is operated on a cash rent basis. In the rare cases, 
where obtainable, cash rent usually amounts to from 3.5 to 1 per cent 
on the investment. It was found in eastern North Dakota, where 
the average selling value of land is approximately 850 per acre. that. 
in general, when a farmer buys land, paying one-half the cost price 
in cash, the remaining $25 per acre is liquidated in about 15 years, 
interest being allowed at 6 per cent, indicating that he has made a 
net income of at least 82.50 per acre per year. 
For purposes of calculation, if 6 per cent on the value of the land 
is assumed for use of land, no serious error will be made. In the 
Eed Eiver Valley this interest amounts to 82.97 per acre; in east- 
central North Dakota. 82.12: in west-central. 81.77: and in the west- 
ern part. $1.34 per acre. 
LABOR OX CROPS. 
Alan labor is one of the important factors of production. The 
amount required per farm was indicated on page 9. The amount 
required per acre for the leading crops under normal yields is shown 
in Table I. 
