LEAFLET No. 33
AIDS to PLANNINGan
ARTIFICIAL CURING
SYSTEM for HAY
J. L. BUTT, Associate Agricultural Engineer
Artificial curing of hay has become a
common practice in many parts of the
Nation. The farmer whose margin of profit
depends upon a continuous supply of high
quality feed for his cattle is responsible
for the rapid adoption of this method of
preserving forage. Artificial curing is popu-
lar because it reduces field losses due to
leaching by rain and dew, bleaching by
sun, and shattering of leaves during the
field handling operations. It also helps to
eliminate the risk of losing a crop due to
bad weather, since artificial curing does
not depend upon atmospheric conditions
for drying air. When done properly, losses
of hay and property due to spontaneous
combustion are eliminated by artificial
curing.
PROCEDURE for ARTIFICIAL
CURING
When alfalfa hay is cured artificially, it
is mowed and allowed to cure in the
swath for about 3 to 4 hours. Then it is
windrowed and left in the field another
1 to 2 hours. The hay should be placed
on the drier just before the leaves begin
to shatter. This 4- to 6-hour period of
field curing will usually reduce moisture
content of the hay from about 75 per
cent at time of mowing to about 40 per
cent. This means a considerable saving
in cost of artificial drying, since most of
the water will be evaporated by the sun.
Data in the following table show the
amount of water that must be removed to
produce a ton of 20-per cent moisture hay:
MOISTURE
CONTENT
OF HAY
Per cent
75
60
50
40
35
25
20
WATER TO BE REMOVED TO
PRODUCE A TON OF 20-
PER CENT MOISTURE HAY
Pounds
4,400
2,000
1,200
667
462
133
0
After the hay has been placed evenly
on the drying floor, the fan and heater
should be turned on and operated continu-
ously. Usually, the hay will dry in about
60 hours if the conditions described in
this leaflet are followed. It will be neces-
sary to check the top layer to be sure
it has dried thoroughly. The curing time
will vary considerably because of condition
of the hay, weather, and efficiency of the
drier. After the hay has been checked
and appears dry, the fan and heater should
be turned off. After 18 to 24 hours, it is
advisable to turn on the fan for a few
minutes and again check the hay for warm
AGRICULTURAL EXPERIMENT STATION
ofthe ALABAMA POLYTECHNIC INSTITUTE
E. ~ ~ ~ ~ ~ ~ ~ ~ fe V.SIH ietr uun lbm
E. V. SMITH, Director Auburn, Alabama
MARCH i1952
spots, musty odor, or other signs that
might indicate spots of uncured hay. If
no such signs are found, the hay may be
considered safe for storage. CAUTION:
If the hay is not distributed evenly and
loosely over the drying floor, there will be
packed areas through which the drying
air will not pass and moldy hay will result.
DETERMINING EQUIPMENT NEEDED
Air Requirements. To select a fan of
the proper size, the quantity of air needed
must first be determined. Where supple-
mental heat is supplied, an air flow of 600
cubic feet per minute (c.f.m.) per ton of
cured hay is sufficient. If natural air alone
is used, the hay should receive at least
800 c.f.m per ton of cured hay. Therefore,
to determine the size fan to select, multiply
the maximum number of tons of cured
hay that will be placed on the drier at
one time by 600 c.f.m (or 800 c.f.m if
using natural air) and the result will be
the volume of air needed. For example,
if 20 tons of hay (27 tons before drying)
are to be placed on the drier (20 tons X
600 c.f.m. per ton = 12,000), 12,000 c.f.m.
of air will be needed.
Fans and Blowers. There are many
different types of fans capable of delivering
12,000 c.f.m. of air, but they are not all
suitable as hay-curing fans. A fan used to
dry hay must be capable of delivering
this quantity of air through the hay in spite
of the resistance to air flow offered by the
hay. This resistance in loose hay 8 to 10
feet deep, may be as muchas 1 inch static
pressure' (in chopped hay, 132 inches).
Therefore, in selecting the fan, one should
be chosen that will give 12,000 c.f.m. at
a resistance or static pressure of 1 inch.
The types of fans generally used in hay
curing are forward curved and backward
curved centrifugal blowers, and propeller
fans. Forward curved centrifugal blowers
are relatively low-priced, operate quietly,
but tend to overload the motor at low
static pressures. Backward curved centri-
fugal blowers cost more, but do not over-
load. Propeller fans are low priced, non-
overloading, but noisy.
Electric Motor. After the fan has been
selected, the size of the electric motor
needed to drive the fan can be determined
from the fan catalog which should ac-
company the fan. In general, the fan
1 1 inch of static pressure refers to the
lateral pressure of the air under the hay,
which is enough to elevate a column of
water in a U-tube open to the atmosphere
by 1 inch.
Stage of Approximate
curing moisture content
per cent wet basis
At mowing
time
After about
4 hours sun
(before leaves
shatter)
After about
6 hours sun
(leaves will
shatter)
Drums (55gal.) of water that must be removed
from each ton of cured hay
75
40
35
lie ..... oil 9.56 neded
.1.45
S1.00
Most of the moisture in alfalfa is removed during first few hours in the field. Drying
economy will be obtained if hay is field cured until just before leaves begin to shatter,
and then placed in drier for finishing.
[21
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Types af fans use'd far artificial drying:
Upper left - forward-curved blade cen-
trifugal; upper right - backward-curved
blade centrifugal; right - propeller type.
'.fiilj( dlixi 1500( toi :,50 (Alm. foi
liii'. ii sp % l Most1 IIIi u i11 illa ilic ar. to
Belts- ad Pulleys. motrt'.,c ti 5 liiX
H iii il limi tll i ofX t ill% drlie~r fair
,oo tilli mak it iccsa, to) d11111
l tic C.igoncitr ol fi CII to Xparis do.-1
la Ciilt t ll. scui o r par XX t i tic' the( fxir st s i/c
'1111. li I schi I' ctcd ii to th~ hc poer fll
.1111 rii.t~iu frj lu l oori al
Heauter. \ fr~itsof~ tl ppi Ici of abit
;u( I' tliild ' f irii t 1. ) a t s 30
.ai'.fithC ill \lr\u acicolrding),ll to th lad
ir t Ip . i h\ tI I f I XX Ii I fill '6 1 / i (Iof
b\ (I I( a11 i I I.fff I ~ ~ ur I I ) I .o
I t t (.r, I , ifi I ri s I )bf (too I 11 1. t' .2 [)(
131ll .For i i~ dalp I llS j12 tilli c f1 r BritiJi.
houraioth i.( of, ict r Bitdc. .i.110 o
tlre a t oil~ the ir t ideul ofC til e fli ta.
of1 I pound1 o11 f XXte lt f rom :iI 32 'F to 212' F.
direct heaters burn in a vented fire box
and the air is passed around the box. Di-
rect heaters are more efficient, since all of
the heat is used; indirect heaters are gen-
erally considered safer from the standpoint
of fire hazard. Heaters may be purchased
to burn any particular fuel that is locally
available. The most commonly used fuels
are fuel oil, propane, butane, and natural 
PX 4" SPACER
gas. The selection of the type of fuel BLOCKS
depends largely upon availability and local
price. Safety controls that should be on
the heater are (1) one to cut off the fuel .
if the fan should stop, (2) one to cut off 
IN DUCT
the fuel if the electric current fails, (3) D/I/NONOFDCTX-2
one to cut off the fuel if the pilot goes out, DETERMINED BY VOLUME
(4) one to select the 
desired temperature,OAITOBDEVR
and (5) an upper limit temperature cut-
off switch. A local fire insurance agent 6" SPACE TO ALLOW AIR TO
PASS UNDERNEATH DRYING
should be consulted before a heater is FLOOR.
installed. Some heaters are approved by
Underwriters Laboratories and are as safe
V IEW OFMANDC
as the heaters used in homes. VIEW OF MAIN DUCT
Other Equipment. In addition to the
equipment comprising the drier, the fol-
lowing are labor savers: hay track with
winch and forks, blower for loading chop-
ped hay, hay loader for loading loose hay
on wagons and forage harvester for field
chopping from windrow.
PLANNING AIR DISTRIBUTION
SYSTEM
The design of the air-distribution sys-
tem will depend upon the barn or other
structure in which it is to be located.
Hence, many different types of systems
have been built to suit varying conditions.
If a few rules are followed, most of these
systems will perform satisfactorily.
Main Duct. The main air duct that con-
nects to the fan outlet is sometimes located
in the center of a mow and sometimes to
one side. Its purpose is to channel air from
the fan to the drying floors located under A SLATTED FLOOR HAY DR
the hay. Regardless of where it is located,
it should be large enough so that the air DIMENSIONS, FAN AND 
.. HEATER SlZ
inside-will not move faster than 1,000 AND OTHER DETAILS 
ARE EXPLAINE
feet per minute (f.p.m). To determine this
sizeQ divide the c.f.m, 
delivered by the 
THIS LEAFLET.
[4]
LOUVRES TO PERMIT ESCAPE
OF MOIST AIR
SEALED WALL
I"X8" FLOOR 
JOISTS
SPACED 2'-0" 0.C.
MOVABLE SECTIONS
FOR CLEANING
(3" SLATS SPACED I" APART
18"NEXT TO WALLS SEALED
TO PREVENT AIR LOSSES
- HEATER
ING SYSTEM
s, LOUVRE OPENINGS,
) ELSEWHERE IN
[5]
fan by 1,000 and the result will be the
size opening required in the duct. For
example, 12,000 c.f.m. - 1,000 f.p.m. =
12 square feet of opening in the duct. The
inside dimensions of the duct then could
be 3 by 4, 2 by 6, or 312 by 38, feet
or whatever size best fits the fan discharge
opening and is at least 12 square feet.
Sometimes when the drier is not fully
loaded, it will be found that more air
passes through the hay that is farthest
from the fan causing uneven drying. This
can be corrected by placing boards or
other obstructions in the main duct to
distribute the air. Boards should be placed
about one-fourth of the way down from
the fan to block one-fourth of the area,
half way down to block half of the area,
and three-fourths of the way down to
block three-fourths of the duct area. By
blocking off in this manner, the air will
be forced to feed more uniformly from the
a Drying fl oor All
FOR MOW WITH OPEN WALLS
Main
D r y i n g fI oar
FOR MOW WITH TIGHT WALLS
FOR NARROW MOW
main duct. If the main duct is located
centrally, is 8 or more feet wide, and is to
have hay stacked on top of it, a means
for allowing some air to enter the hay
above the duct must be provided. This
can be done by leaving 1- to 2-inch cracks
at 2-foot intervals for the length of the
main duct. These cracks should be covered
by boards supported on spacer strips to
keep hay out of the duct.
Drying Floor. The drying air is dis-
charged from the main duct underneath
the drying floor. The drying floor sup-
ports the hay and is provided with open-
ings for the air to penetrate the hay. To
permit occasional cleaning, drying floors
are usually made in portable or movable
sections small enough to be handled
by two men. These sections consist of joists
that rest on the original mow 
floor and on
top of which are nailed 1- by 8-inch boards
D rying floor 
MOW WITH MAIN DUCT BELOW FLOOR
MOW WITH MAIN DUCT BELOW FLOOR
MOW WITH MAIN DUCT AT SIDE
Main duct and drying floor
DRYING FLOOR AS MAIN DUCT
Shown above are some of the systems commonly 
used. Regardless of the one used,
the hay should be stacked so that the air will 
pass through the same thickness of hay
in all directions.
[6]
C11Ctn~~l~rP +I7P Rlr nnnrn~ cMrrllln np nia~pn n~rr rn
about 1 inch apart. It is referred to as a
"slatted floor" system. The 
joists should
be rough 1- by 8-inch boards spaced about
2 feet apart. The butt ends of the joists
farthest from the main duct should be
covered with boards. In hay mows where
the hay can be stored level on the top
from wall to wall, the drying floor should
extend to the wall. In mows where the
hay must be stacked higher at the center
than at the sides, the drying floor should
end about 6 feet from the outer edge of
the stack. This is to insure that air will
pass through the same thickness of hay in
all directions.
General information. Enough open area
must be provided overhead to permit the
moist air leaving the hay to escape before
it condenses on top of the hay. This is
done by having louvers, windows, or other
openings around the top of the mow.
There should be at least one square foot
of opening for each 200 c.f.m. of air de-
livered to the hay. For example, if 12,000
c.f.m. is to be delivered (12,000 + 200=
60), 60 square feet of opening should be
provided.
The roof and walls should be weather-
tight and the floor should be strong enough
to support the hay, bearing in mind that
it will be about 35 to 50 per cent heavier
due to high moisture content. In addition,
the floor must be air-tight to prevent
loss of drying air.
If hay chutes or other openings exist
in the mow, they must be boarded up
to prevent a loss of air. Obstructions in
the mow such as posts also allow air to
escape because the hay does not pack
tightly against them. Hay should be tramp-
ed around such obstructions to avoid this
loss.
BALED HAY DRYING
Experiments in baled hay drying are not
yet considered entirely satisfactory. While
some excellent hay has been obtained, oc-
casional "slow-drying" bales have resulted
in moldy spots or excessive drying time.
Experiments' to date have resulted in the
following observations: (1) There should
be at least two layers of bales, staggered
to eliminate cracks (the maximum depth
has not been determined); (2) the bales
should be stacked together as tightly as
possible and all large cracks between bales
stuffed with hay; (3) the baler should
be adjusted for the loosest possible bales
that will stand careful handling; (4) the
cut side of the bale should be placed
against the drying floor, since air seems
to flow best through that side of the bale;
and (5) the operating cost of drying baled
hay is about twice that for loose hay.
PORTABLE DRIER UNITS
There are a number of portable and
semi-portable driers on the market. Fans,
heaters, and controls are mounted together
and sold as a unit. This eliminates the
necessity of buying the equipment piece
by piece and having it installed. With such
units, a size must be selected that will
meet the minimum air flow and heating
requirements calculated by the method
described earlier. Another advantage 
of
this type of unit is that it may be used
at several locations or in connection 
with
seed and grain drying.
COST of ARTIFICIAL DRYING and
EFFECT on QUALITY
Tests conducted by the Agricultural Ex-
periment Station of the Alabama Poly-
technic Institute and by other experi-
ment stations throughout the country
indicate that loose or chopped hay can
be dried at an operating cost (fuel and
electricity) of less than $2 per ton.
The following table is from a U.S.D.A.
Mimeograph, March 1950, "New Values
in Good Hay and Silage for Dairy Cows,"
by L. A. Moore, head, Department of Nu-
trition and Physiology.
3 Baled hay drying experiments 
have
been conducted in cooperation with the
Dairy Department.
[7]
Alfalfa cured
as
shown
Crop, as cut
Silage
Barn Cured with heat
Barn Cured no heat
Field Cured no rain
Field Cured rain
Carotene,
per cent
of crop
as cut
100
28
9.7
7.5
3.0
1.0
Dry Matter,
per cent
of crop
as cut
100
84
87
81
75
60
Protein, Expected milk yields,
per cent per cent of
of crop field cured hay
as cut damaged by rain
100
84
78
76
69
49
140
145
185
125
100
Dr. Moore states, "This shows that both
siloing and barn drying have considerable
advantage over field curing, and that field
curing without rain damage has consider-
able advantage over rain-damaged hay.
Under practical farm conditions, the
amount of nutrients preserved by field
curing would probably represent an av-
erage of the amounts preserved in rain-
damaged hay and in hay harvested with
no rain damage. Thus, by barn drying hay
without heat, a dairyman would obtain
about 20 per cent more milk per acre
than by field-curing; by barn-drying with
heat, he would obtain about 30 per cent
more milk per acre. However, the cost
of heat would cut down this advantage.
By making silage, about 25 per cent more
milk per acre would be expected. These
figures, of course, apply to alfalfa and
are dependent on the number of hay crops
that might be damaged by rain.
"The results of these experiments indi-
cate that siloing is the best method for
preserving the nutritive values of the hay
crop. The results also show that barn
drying has considerable advantage over
field curing. Siloing has the advantage
over barn drying in that more carotene
can he preserved because the crop can
be removed from the field with less
chance of weather damage. Whether the
dairyman uses one method or the other is
an individual farm problem. His choice
will depend on the buildings already on
the farm and on the relative .cost of
building a silo and a barn drier.
"In summary, good hay and silage
possess 'values' that are not contained in
poor-quality forage. These 'values' are a
cheaper feed, a source of vitamins and
minerals, a greater consumption of forage,
and an increased digestibility of forage. In
preserving these 'values,' siloing or barn
drying the hay crop is considerably more
advantageous than field curing."
REFERENCES
Cooper, A. W. and Miller, E. L. Planning
and Operating a Mow Hay Curing System.
Mimeo. No. 13. Dept. Agr. Engin. Ind.
Agr. Expt. Sta. Nov. 1948.
McKnight, Ralph E. and associates. Hand-
book on Design of Slatted Floor Barn
Hay-Driers. Dept. Agr. Engin. Va. Poly.
Inst. cooperating with Va. Farm Electrifi-
cation Council. June 1946.
[8]
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