MECHANICAL DEWATERING OF FORAGE CROPS
J. W. Randolph, J. P. Winfree and V. E. Green, Jr.
This report contains results of preliminary tests of
mechanical devatering of crops to ascertain its value
in preparing feeds for soilage, silage, and dehydration.
The equipment, facilities and some of the crop materials
used in the study were made available through the cour-
tesy of Dan B. Vincent, Inc., Tampa, Bel Vita Farms, Inc.,
Belle Glade, and the Fertile Valley Dehydrating Company,
This report was prepared for a meeting of extension and
experiment station personnel to discuss Animal Husbandry
Research at Everglades Experiment Station, Belle Glade,
Florida on April 25, 1958.
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April 25, 1958
Everglades Station Mimeo Report 58-14
Belle Glade, Florida
MECHANICAL DEWATERING OF FORAGE CROPS
by J. W. Randolph, J. P. Winfree and V. E. Green, Jr. /
Water within a forage crop has no feed value and it can restrict the most
effective and efficient utilization of crops or livestock feeds.
Mechanical dewatering, or artificial wilting, is an old process that may
be found in many applications about a farm home. The system herein considered
for the partial and preliminary drying of forage materials is carried out with
equipment which may be described as a modified kitchen meat grinder greatly
One modification is forcing the discharge, which we call a "press-cake",
around a choke-cone that replaces the perforated end-plate. Another variation
in design is the substitution of a screen for the solid wall cylinder around
the screw which has a variable pitch. "Press-liquor" is used to designate the
fluid that is forced through the screen cylinder.
The normal growth cycle of a plant starts with high succulence and high
quality feeding values and it progresses more or less rapidly into a condition
of high fiber content and low feeding values. If the harvest is delayed, the
losses in nutrients may continue to a worthless condition. The progressive
changes in the moisture relationships within a crop are influenced not only by
the stage of maturity but also by moisture conditions as content of soil and
atmosphere. Both moisture factors are generally unfavorable in south Florida
when the crop should be harvested for maximum value.
The normal use of moisture percentage data frequently fails to convey the
true significance of "feed-dilution" as it may apply to pasture grasses or to
the feeding of green-chop forage. In either case, the actual economic value of
the green crop may be limited by the volume-intake-capacity of a cow. Table 1
illustrates the significance of moisture percentage on the total green material
required for 20 pounds of dry matter intake.
The data in table 1, for the higher moisture relationships shows total
quantities that exceed the intake capacity of a 1,000 Ib. steer, which might
have a daily weight gain of 1.25 to 1.75 pounds if the dry matter had less water
dilution. It is apparent that ust-too-much-water' in a forage feed can cause
cattle starvation when a pasture crop is very succulent.
Preliminary tests at the Everglades Station and large-scale use of screw
presses have shown that grasses and legumes, recovered from a standard forage-
crop-harvester, can be mechanically dewatered without additional treatment into
a press-cake with 70 percent moisture. This means that a steer may obtain 20
lbs. of dry matter by removing 200 .-'66 .- 134 lbs~ les 'water from greenchbop
press cake ;containing 70% moisture than from'green chop'that contains 90%
I/ Agricultural Engineer, Assistant Soils Chemist and Associate Agronomist,
respectively, Everglades Experiment Station, Belle Glade, Florida
Mr. T. J. Durrance, Brighton, Florida, the first farmer in United States
to use mechanical dewatering on forage crops was also the first man to feed
dewatered forages as soilage. He has made many favorable observations while
feeding beef and dairy cows and calves large quantities of fresh press-cake
and dewatered-dehydrated millet, sorghum, alfalfa, corn, and pangola grass
forages. According to Mr. Durrance, the forages lost their laxative effects
and the animals consumed a higher level of dry matter as forage. This reduced
the quantity of concentrates they needed and made it necessary to re-evaluate
the ration with respect to balance and nutrient content.
A Historical Note
The studies at the Everglades Experiment Station are in a sense a continua-
tion of experiments in which the senior author took part as early as 1939.
During this time period, equipment manufacturers have made marked improvements
in mechanical dewatering presses and the process has become a standard practice
in many enterprises, including Florida's citrus by-product feed industry.
Again America bows to Europe's technology. The British have continued to
work on high-pressure mechanical dewatering systems as they apply to different
green plant materials. Italian workers have apparently done much more work on
forage crop materials, using a low pressure press of a type or design much like
the unit herein described. Reports indicate that Italian press units are used
on a wide scale, either involved in custom work or used by cooperatives made up
of 4 to 5 small farmers.
Amounts of Forage Required for 20 Pounds of Dry Matter
Percent Moisture Pounds of Grass Required
Dry Supplemental Feeds
Haymaking and even field wilting a forage crop have proved to be impractical
in south Florida when crop growths represent their highest feed values. Due to
the excessive moisture therein, thermal dehydration plants in the past have failed
economically to reduce succulent materials into dry feeds.
This statement takes on real significance when authorities stated in the
spring of 1958, that between 75,000 to 275,000 cattle died in south Florida dur-
ing the past winter. Actual deaths were usually credited to a direct result of
starvation after a "very-unusual-winter" or water that had killed off the pasture
Data in table 2, when considered in respect to the typical moisture percen-
tages that exist in south Florida's forages when in top-quality condition, gives
an old economic justification for the non-existence of supplemental feeds from
local sources. It is to be pointed out that artificial dehydration in the Mid-
west takes place on forage crops that are generally low in moisture 65 percent
may be given as the highest in standard practice.
Production of One Ton of Dry Feed, with 10 Percent Moisture: Calculated
Water to be Evaporated, Fuel Requirements, and Output per Hour.
Pounds of water
to be evaporated
in gallons oil
Output per hour
The above calculated rates and fuel required for the dehydration of forages
that are very high in moisture will not hold true in practice. Such chopped
materials are a watery-viscous mass that defy mechanical breakup actions that
would fully expose each small plant part to the hot air currents within a dehy-
drator. Hence, the drying process is very slow and often thin leaf sections
are burned to a char before the mass is dehydrated.
A forage crop is normally selected and grown on the basis of a farmer's
ability to make hay or silage using natural methods of curing and processing.
A new prospectus in growing a crop for cattle production may be centered on
crop yields in terms of feed qualities, the period when available, the associated
farm work requirements, and the degree of response to mechanical dewatering and
other physical operations leading up to direct feeding, silage making, and arti-
Table 3 gives data on the response of different crop materials to mechanical
dewatering. This information was obtained with three presses loaned by Dan B.
Vincent, Inc., Tampa, Florida, and data collected both at the Durrance Ranch,
Brighton and Belle Glade, Florida.
Response of Different Crop Materials to Mechanical Dewatering
Crop Material Original Percent Percent Dry Matter After
Dry Matter One Pressing Two Pressings
Snap Bean plants
White Dutch Clover
Green sweet corn stover
The new prospectus for an abundant supply of dry feed for south Florida
cattle needs and for a sizeable surplus is based upon sufficient evidence that
the improved farm lands of this area can produce exceptional yields of high
quality forages. Table 4 contains a list of some of the crops adapted to the
Everglades and some crop waste materials therein available in large quantities.
This list has been subdivided as to the season of availability and the feed
characteristics of the crop or parts.
Agriculture in south Florida is confronted with two problems that will
delay the mechanization of forage feed making and processing, although mechanical
dewatering should eliminate a large part of the gambling aspects heretofore asso-
ciated with harvesting and processing. There is a need for much research work
on the selection of crops, development of varieties to fit specific requirements,
and testing of cultural practices that will provide quality materials, at low
cost, over long periods, and within conditions of balance associated with other
items of good farm management.
The second and the major problem to an efficient forage crop processing
program would be the necessity for field crews to keep a balanced supply of
raw material at dehydrator for around-the-clock operations, a condition of para-
mount importance for maximum efficiency and the lowest unit costs in artificial
dehydration. There is no need to list the inherent limitations and frequent
troubles associated with available harvesting equipment, because the machines
were never intended to handle crop-tonnage as it can be produced in the
Mechanical Dewatering As An Aid to Silage Making
The responses of different crop materials to mechanical dewatering, table
3, may be highly important factors to be considered in silage making. J. A.
Newlander and W. H. Riddell of the Vermount Agricultural Experiment Station and
others have established:-
The principles of making good silage
are proper moisture content (60 to 70
percent) and good packing.
The data in table 5 indicates that high quality silage can be made from
high moisture forage materials after dewatering and without additives or preser-
vatives. Special attention is called to the dewatered celery-top-silage data
in table 5.
Season of Availability and Relatil
Crop or Crop Material Nov. 15 to Feb. 28
H P 1
0 0 ,0 w
Texas 610 Sorghum
Sugar cane, whole
Field corn, whole
M VH L L VH
L VH M L VI
VH VL VH VH VL
VH VL VL VE L
Sugar cane tops
Green Bean vines
Note L t Low
M : Medium
L VH -
H M H
H H M
H M H
VH : VWry high
VL s Very low
Influence of Mechanical Dewatering On Density and pH of Silage
Silage from original Silage from press-cake
Percentage Dry Matter Percentage Dry Matter
Crop Material Moisture Per cu./ft. pH Moisture Per cu. ft. pH
Chinese Cabbage 6.1 2.29* 77.3 12.92 3.9
Turnip tops 93.9 3.63 4.4 74.0 18.07 4.1
Celery tops 91.8 3.58 4.6 64.3 22.94 4.2
Green oats 85.7 6.29 3.9 67.7 16.31 3.9
Sweetcorn stover 80.6 8.87 3.8 73.8 15.51 3.8
Pangolagrass 82.1 8.12 4.3 72.6 15.41 3.9
Paragrass 81.2 5.82 4.8 75.9 9.94 4.2
Caribgrass 80.6 7.01 4.8 73.3 13.58 4.0
St. Augustinegrass 78.1 8.38 5.0 74.6 11.90 4.3
Note 1/ A pH of 4.2 or below is desirable.
* Silage spoiled.
The process of mechanical dewatering drives out a relatively small amount
of dry matter in the press liquor. The favorable economics associated with the
press-cake will in most cases offset the losses in the liquor.
The press-liquors from many different crop materials are more or less homo-
geneous, but by any of several methods of treatment may be divided into a semi-
clear liquid and a sludge which may then be separated readily. British investi-
gators use the words 'grass-cheese' to describe the small quantity of solids
that can be removed from the liquor. Grass-cheese is high in desirable feed
properties and very low in fiber. The clear liquid contains appreciable amounts
of minerals, which could be returned to the land as a fertilizer.
Chemical Changes in Press-cake
Chemical changes indicating nutrition values in forage materials that have
been mechanically dewatered may best be illustrated by Tables 6 and 7. The data
are for four of the most commonly used and recommended pasture grasses of the
Everglades: St. Augustine, Pangola, Carib and Para, all growing under the same
environmental and cultural conditions.
Percentage; Minbrhl Ash
Average 15% Decrease
16% decrease 54 decrease
crude protein N times 6.25 equals the commercial value of
I i I
I I I I II I
Advantages and Disadvantages
Information gained from the many indicated combined sources is the basis
for the following outline summary of mechanical dewatering of forage crops:-
I. Advantages in feeding press-cake over green-chop to cattle
1. Increased intake of dry matter and increased T.D.N., hence with
adjustments in ration less supplemental feeds are required.
2. Reduces a cow's selectivity for plant parts or species due to mix-
ing and inter-compacting, hence less throw-out and refusal losses.
3. In certain cases appears to reduce digestive disorders and to
improve the general sanitation conditions about a feeding area.
II. Advantages of feeding press-cake over pasture grazing
All the above plus:-
4. Reduces the weed problem in that broadcast cutting is required.
5. Less trampling and loss of stand in a pasture, hence yields per
acre are increased.
6. Utilizes urine and manure spot forage.
7. Makes possible obtaining forage at maximum nutritive stage within
a system of crop and land management that requires no temporary
or special fencing.
III. Advantages of mechanical dewatering in silage making
8. Increases the amount of dry matter that can be put into a silo.
9. Increases the rate and the degree of the ensiling or the preserva-
10. Reduces the need for preservatives or additives.
IV. Advantages of dewatering for thermal dehydration
11. Speeds up and adds to completion of the dehydration process.
12. Reduces costs and increases the output rate.
13. A dehydration enterprise may be reduced to a standard practice
because of a near-like raw material insofaras water to be evaporated.
V. Disadvantages of dewatering
1. Requires an initial high investment in machinery.
2. A dewatering press must have stainless steel in the functional
parts, hence farm repairs are difficult.
3. A forage-crop-harvester with a dewatering press attachment is not
yet available, hence the need to delay economies in farm transporta-
tion and returning press-liquor fractions back to the land.
APPENDIX TO MIMEO REPORT 58-14 TABLE 8
PROXIMATE ANALYSIS/ OF SOME PLANT MATERIALS AS AFFECTED BY MECHANICAL DEWATERING
Plant Series Percentage Calculate
Material No. Dry Matter Protein Fat Fiber NFE Ash TDN
(Percentage of Dry Weight)
1/ The chemical analysis (courtesy of A. Duda and
Thornton Laboratories, Inc., Tampa, Florida.
/ Fresh Chop
3/ K = Press Cake; KX : Press Cake (2 Pressings)
Sons, Oviedo, Florida) were performed by