12 BULLETIN 873, U. S. DEPARTMENT OF AGRICULTURE. 
that hay usually becomes that dry or that the hay grower should 
expect such a low water content under average conditions. A low 
minimum water content is reached naturally only during very unu- 
sual conditions, such as a long exposure in a very dry and hot climate 
like that found in the Southwest. Neither should it be expected that 
the water content, having once reached the minimum, will remain 
constant, unless the temperature and humidity of the air remain 
constant, a condition which does not prevail in the larger part of the 
hay-growing section of the United States for any great length of time. 
From the data presented it is shown that the minimum water con- 
tent of timothy is 6.1 and of alfalfa 4.6 per cent. The minimum for 
the other kinds of hay is slightly higher—the average for all being 
6.52 per cent. If the average or normal water content figures are 
averaged for all of the hays for which the minimum has been figured, 
it is found that hay, in general, contains about 10.32 per cent of 
water when well cured. The difference between the two averages is 
3.6 per cent. 
FIFTH FACTOR—ATMOSPHERIC HUMIDITY. 
The water content of cured hay in the stack, barn, or bale is subject 
to fluctuations, caused by changes in atmospheric humidity which is 
the fifth factor to be considered. If hay contains a larger percentage 
of water than does the air there will be a loss by evaporation. If 
the hay is drier than the air it will absorb water. A change in 
humidity affects a small quantity of hay to a relatively greater extent 
in a given time than it does a large bulk. 
Oat hay was baled on June 1, 1913. The average loss during July and August, when 
the weather was unusually dry and hot, amounted to 1.4 per cent. Small samples, 
weighing 44.5 ounces, taken from the bales and inclosed in cotton bags and suspended 
wnder shelter, where the air could circulate freely, lost an average of 4.3 per cent 
during the same period. Again, on June 1, 1913, four large bales of oat hay, averaging 
243.8 pounds, were made. The loss by August 1 amounted to 9.8 pounds, or 4.02 per 
cent. During the first 25 days of September there was an aditional loss of 3.4 pounds, 
or 1.4 per cent. From September 25 to December 1 there was a gain of 1.4 per cent, 
which brought the weight back to 234.1 pounds, the weight on August 1. 
Experiments with small bales of oat hay made the following year (1914-15) showed 
a much larger proportional fluctuation. The bales weighed, on an average, 178 pounds, 
or one-third less than the large bales used the year before. The small bales, baled on 
June 1, 1914, had lost 8.1 per cent by August 31. From that date until February 25, 
1915, they gained a total of 5.9 per cent, making the net loss from June 1 to February 
25 but 2.2 per cent. The loss was attributable to the dry weather during July and 
August, and the gain to the wet weather during the winter months. 
It should not be inferred, from the results of experiments to date, 
that hay in small bales will always lose more by shrinkage, or that their 
normal water content will be subject to a greater degree of fluctuation 
than that of hay in large bales. Information is lacking on the one 
14 U. S. Department of Agriculture, Bull. 353, 1916. p. 32. 
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