Iltbcral Hrts
Mpechnoloigg
STATION BULLETIN 435 NOVEMBER 1956
The Influence of Waste Bark
on Plant Growth
By Stuart Dunn
SUPPLEMENT
The Comparative Value of Bark
as a Surface Mulch for Apples, Blueberries,
and Raspberries
By L. P. LATIMER
AGRICULTURAL EXPERIMENT STATION
UNIVERSITY OF NEW HAMPSHIRE
DURHAM, NEW HAMPSHIRE
Acknowledgements
The experimental work herein reported was made possible by a
research grant from the Brown Company, Berlin, New Hampshire.
The planning and supervision of the project was the responsibility
of a supervisory committee consisting of the following: L. T.
Kardos, Agronomy Department, Chairman; Stuart Dunn, Botany
Department; L. P. Latimer, Horticulture Department; Lewis Swain,
Forestry Department; G. P. Percival, Agricultural and Biological
Chemistry Department; and Edward Katz, Bacteriology Depart-
ment. Most of the work of caring for greenhouse cultures of plants
and field plots was done by L. P. Wolfe, Jr., and W. A. MacDonald.
The Influence of Waste Bark on Plant Growth
By STUART DUNN
Plant Physiologist
New Hampshire Agricultural Experiment Station
Introduction
MANY pulp and paper manufacturers, including the Brown Company,
Berlin, New Hampshire, have to dispose of several tons of fresh bark
produced at the mill every day. Present practice is to truck it away and
dump it. This necessitates the use of trucks, grading equipment and labor.
Experiments, therefore, were started in an effort to discover, if possible, a
profitable outlet for waste bark, including possible benefits to agriculture
through soil improvement.
A search of the literature reveals that very little work has been done on
the effects of bark from pulpwood on soil and plants. Very little has been
published on the subject. Rettie and Simmons (6) report that water-soaked
bark, as it comes from the barking drums, contains upwards of 80 percent
moisture. In this condition the fuel value is almost nil. Other reviews (5)
indicate that bark may have possible industrial uses as well as soil building
potentialities.
Studies with sawdust (1, 3, 4, 7) applied either directly to soil or as
compost show that when well decomposed it may in either case benefit
plant growth.
The experimental work with bark may be divided into two parts: (1)
that dealing with greenhouse pot and bench cultures, and (2) field plot
trials, and will be considered in that order.
Part I Greenhouse Cultures
Effects on Plant Growth of Various Ratios
of Bark to Soil and of Peat to Soil
An attempt was made to determine what proportion of bark or peat mixed
with soil is necessary for optimum plant growth, compared to soil alone
as control. Peat was used in this and many subsequent tests because it is
a standard merchantable organic material used as a soil improver, and bark
would have to compete with it in the market. The bark materials used were
of four types: new softwood bark, new hardwood bark, old softwood bark,
and old hardwood bark. The term 'new' means that the bark was fresh
from the mill; the term 'old' means that it had been standing in piles for
several years and was partly weathered and decomposed. Some of this latter
material was in a fine powdery condition. The concentrations used for each
of these and for peat were 10, 30, and 50 percent by volume as shown in
Table 1. Each was thoroughly mixed with soil in these proportions. Enough
of each mixture was prepared to fill 10 pails of 14-quart capacity. These
pails were previously coated on the inside with a waterproof varnish.
Table 1. Average Yields (Grams) of Three Successive Crops: Bark-soil,
Peat-soil Mixtures, and Soil Controls
Cabbage
Radish
Com
Percent
Dry Wt.
Fr. Wt.
Dry Wt.
Organic Matter
Treatment
of Tops
of Roots
of Tops
Old softwood bark
18.8*
73.0
10.8
Old hardwood bark
16.2t
89.3
11.2
10
Peat
14.3
88.1
11.3
New hardwood bark
13.3
70.7
11.2
New softwood bark
12.0
58.8
11.0
Old softwood bark
17.0*
15.2
11.5
Old hardwood bark
15.3
7.1
12.0
30
Peat
12.2
%.7+
11.6
New hardwood bark
5.5
23.5
11.9
New softwood bark
3.6
12.9
12.2
Old softwood bark
14.6
1.7
14.0
Old hardwood bark
11.6
3.6
12.8
50
Peat
10.0
70.9
14.9
New hardwood bark
2.3
8.3
12.1
New softwood bark
1.3
4.9
11.7
Soil only — Control
14.1
123.6
12.3
* Mean of yields significantly greater than controls at the 1 percent level.
t Mean of yield significantly greater than controls at the 5 percent level.
t Control not significantly greater at the 1 percent level.
Three successive crops were grown in these mixtures in the following
order: (a) cabbage, one plant per pail; (b) radish, four plants per pail;
and (c) field corn (Kingscrost) , two plants per pail. About midway in the
growth of the cabbage, a nutrient solution was supplied to correct defici-
encies. Subsequent crops received fertilizer when soil tests indicated their
need. Between the radish and corn crops the mixtures and soils were allowed
to remain fallow for 6 months.
The yield results appear in Table 1. There are several noteworthy points.
(1) Cabbage was the only crop showing yields significantly greater for
bark than for the soil controls; two of those yields were for old softwood
bark and one for old hardwood bark. The generally more advanced state
of decomposition and finer texture of these old barks compared to new bark
was probably largely responsible for this. Yields for plants in peat-soil
mixtures were close to that for the control. (2) With increasing concentra-
tion of organic matter, the growth of cabbage was consistently poorer. (3)
At the 30 percent concentration and above, except for the old softwood
bark, there was no advantage in the use of bark or peat. (4) In the new
barks, growth was very poor at the 30 and 50 percent levels of concentration.
With the radish crop all yields in bark or peat mixtures were much lower
than the controls. However, the plants in the peat mixtures at the two higher
proportions of 30 and 50 percent yielded much better than those in the
corresponding proportions of any of the bark mixtures.
With the corn crop, growth in all the cultures was very uniform. Statistical
analysis showed no significant variations from the controls. The decay of
the organic matter during two previous crops, plus a fallow period, was
probably largely responsible for this. There was a slight tendency for the
growth of plants in the 50 percent mixtures to be better than in the 10
percent mixtures. The fact that the plants of the two previous crops in the
50 percent mixtures had been poorest of those grown in any of the three
proportions of organic matter indicates that, even in this highest concen-
tration, decay was well advanced.
Effect of Bark and Peat on Flower
Production by Ornamentals
A snapdragon crop was grown in benches, followed later by a carnation
crop. Three standard greenhouse benches were prepared in the following
manner:
Bench No. 3 — Regular greenhouse compost made up of manure,
soil, sand, and plant waste.
Bench No. 4 — A mixture of peat (25 percent) and greenhouse
compost (75 percent) by volume.
Bench No. 11 — As above, except that 25 percent old hardwood
bark was used in place of peat.
All of the materials in each bench were thoroughly mixed and steam
sterilized. Tests showed sufficient nutrient present and pH levels satisfac-
tory in all benches (6.0 to 6.6).
Snapdragon plants were set out in the benches on December 5, 1950.
Each bench contained three varieties as listed in Table 2. All plants had
been pinched because of their size when transplanted. No fertilizer was
applied at this time nor during the experiment. On February 19, 1951,
more than a year later, the first harvest was made. At this time and at
each cutting for the following two weeks, the greatest number of flowers
was harvested from the bench containing bark. In succeeding harvests the
number of flowers cut from each bench tended to become equal. The total
yields given in Table 2 show greatest production for the bark, next largest
Table 2. Total Yields of Flower Harvest from Greenhouse Beds
Treatment
Bark 1/4, Soil %
Peat 1/4, Soil%
Soil Only
Snapdragons — Variety
White Wonder
Yellow Ethyl
Pink Peggy Schoroman
246
239
279
225
208
223
205
202
204
Total of all varieties
764
656
611
Carnations — Variety
Cardinal
Harlequin
Olivette
Wm. Simm
225
261
212
206
223
285
240
207
213
281
241
187
Total of all varieties
904
955
922
for peat and lowest for soil (compost mixture). Records were taken also
on the length of flower stalks. The averages were: bark 61.3 cm., peat 77.6
cm., and soil 78.2 cm.
After the final snapdragon harvest, the contents of each bench were steam
sterilized without moving them. Four varieties of carnation transplants were
installed in equal numbers per bench. The varieties are listed, together with
a summary of total yields of flowers in Table 2. Here the greatest total
yield was given by the plants growing in the peat mixture, but probably
none of the differences is very significant.
Apparently, in a highly organic compost mixture, such as the basic ma-
terial used here, relatively little benefit was secured from additional organic
matter such as peat or bark. However, bark might have some advantage in
not rotting as quickly as many organic materials now in general use in
greenhouse composts.
In connection with this work on ornamentals, mention may be made of
a small experiment on orchids. Three orchid plants were planted in old
hardwood bark on January 15, 1952. Nothing else was added. On December
15, 1952, these plants appeared to be perfectly healthy, and two of them
had produced flowers. Old bark may be regarded as a satisfactory medium
for orchid growing.
Comparative Effects of Bark and Other
Wood Wastes on Plant Growth
Since considerable experimentation has been done with sawdust and other
woodwastes (1, 3, 4, 7), it seemed of interest to compare plant growth in
bark with several of these. The materials tested in this comparison are listed
in Table 3. Ten one-gallon size cans were filled with each material. They
were used in the pure state, i.e., no soil was mixed with the organic sub-
stances. A good loam potting soil was used as control. At the beginning of
the experiment 10 grams of 5-10-10 fertilizer was applied to each can.
Two crops were grown: cabbage, one plant per can, followed by barley,
fifteen plants per can. Between crops the contents of all the cans for each
kind of material were re-mixed together and 3.5 grams of fertilizer added
per can. The yields, as given in Table 3, show that plants grew much better
Table 3. Average Dry Weights (Grams) of Two Crops Grown
In Waste Bork and Other Woodwastes
Barley,
Cabbage,
Mean Dry Wt.
Mean Dry Wt.
of 9 Cans
Treatment
of 10 Plants
15 Plants/Can
Old hardwood bark
7.8*
5.4*
Old softwood bark
7.1*
4.1*
Vi sawdust, y<2, old softwood
bark
7.0*
3.2
Soil control
5.1
2.8
% shavings, % silage
3.2
7.0*
Fresh sawdust
2.6
3.7
Birch shavings
1.7
0.8
* Mean of yields significantly greater than controls at the 5 percent level.
6
in the old barks than in fresh sawdust and shavings. If they had been com-
pared directly with composted sawdust in this respect, the story might
have been different ( 1 ) .
Effects of Old Bark-Soil Mixtures
Without Fertilizer on Bean Yields
Old hardwood and old softwood bark were mixed each with soil in the
proportion of % bark to % soil and Tiny wax beans grown in them in
comparison to soil only as control. Fertilizer was omitted in order to de-
termine something of the effects of the bark alone on plant growth. The
plants were grown in ten-inch pots, with two plants per pot and twenty
pots per treatment. The results in yield of seed appear in Table 4. The
better yield of the plants grown in soil alone further strengthens the case
Table 4. Yields of Seeds of Wax Beans Grown !n Soil-Bark Mixtures, No Fertilizer
Soil Control
Vs Old Hardwood
Bark, % Soil
% Old Softwood
Bark, % Soil
Ave. No. of seeds
from 20 plants
Ave. Wt. (grams) of seeds
— 20 plants
39.8
17.2*
28.5
12.8
31.4
14.5
* Significantly greater than other yields at the 5 percent level.
that most of these organic soil supplements will not support or promote
good plant growth without liberal amounts of fertilizer. This is still further
emphasized and supported by the results on tomatoes given in the following
section.
Effects on Tomato Yields of Pure Old Bark
Compared to Soil With Added Fertilizer
This was an experiment to determine something about the influence of bark
alone (not mixed with soil) on plant growth. The two old barks were
studied in comparison with pure peat, and with soil only as control. The
materials were each placed in 10 glazed crocks of 2-gal. capacity. Before
planting, 20 grams of 5-10-10 fertilizer was mixed with the contents of
each crock. Young tomato plants of the New Hampshire Victor variety were
transplanted, one to each container. Early in the course of this experiment
all of the plants in pure peat died, evidently because of the low pH. There-
fore, no yield data is available for the plants in this material. After the
other plants had been growing for nearly two months 5 grams of ammonium
nitrate were added to each crock as supplementary nutrient.
As the plants matured, records were kept of the yields of fresh ripe
fruit from each plant. The yields are given in Table 5, as well as the aver-
age weight of the individual fruits from each material. The average yields
for both bark treatments were considerably greater than for the soil con-
Table 5. Yields of Tomatoes Grown in Pure Bari< Compared to Soil — Fertilizer Added
Old Soft-
wood Bark
Ave. yield of ripe fruits
per plant (10 plants). 730.5
Ave. weight of individual fruits 60.3
Old Hard-
wood Bark
494.2
62.5
Soil Control
315.5
45.7
trols, the one for the old softwood bark significantly so. The average size
of fruits was considerably greater for each bark culture than the control.
It appears from this that either one of the old barks makes an excellent
growing medium, if an adequate nutrient supply is maintained.
Effect of Sewage Sludge on Growth of Plants in Bark
This experiment was conducted to determine something of the modifying
effects of sewage sludge on bark as a growing medium. Sewage has been
used extensively in Europe as a composting aid for various materials (2)
and in composts with sawdust at this station (1). Two mixtures consisting
of different proportions of sewage to the two kinds of old bark were pre-
pared, namely, 1 to 5, and 1 to 8. No fertilizer was applied. Cabbage plants
were grown in ten containers (one plant per container) of each of these
mixtures in comparison to soil as a control. The yields are given in Table
6. The yield for each proportion of old hardwood bark to sewage is sig-
nificantly greater than that from the soil controls. The plants in old soft-
wood bark and sewage mixtures did not yield significantly greater than
the plants in soil only.
Table 6. Dry Weight Yields of Cabbage (Tops) Grown in Bark-Sewage Mixtures and in Soil
Treatments
Mean Dry Wt. of 10 Plants
1 part sewage — 8 parts old hardwood bark
1 part sewage — 5 parts old hardwood bark
1 part sewage — 8 parts old softwood bark
1 part sewage — 5 parts old softwood bark
Soil — control
13.9*
11.6*
7.2
6.3
5.6
Mean of yields significantly greater than controls at the 5 percent level.
Root Growth in Bark and Other Materials
The greenhouse operator, nurseryman, and other plantsmen are frequently
concerned with growth of seedlings and getting a good start with them. It
seemed desirable to secure information on seedling root growth in bark
compared to other materials with which it might have to compete on the
market.
The growth measurements of three kinds of seedlings, grown from seeds
planted directly in the medium, are presented in Table 7. New softwood
Table 7. Comparative Tests of Root Growth in Bark and Other Materials
Root Lengths
; in Cm.
— Mean
of 10 Plants
Peas
Onions
Corr
I
Tap
Lateral
Longest
Top
Tap
Side
Pure Materials
Root
Root
Root
Length
Root
Root
Old hardwood bark
24.8
2.7
9.4
9.6
21.9
12.5
Old softwood bark
20.5
3.9
6.5
9.9
23.2
9.3
New softwood bark
12.6
2.8
Sand
10.9
1.6
2.9
6.4
18.1
7.5
New hardwood bark
9.0
2.5
Peat
3.3
LI
2.7
9.7
14.3
8.2
Vermiculite
12.0
9.8
21.9
11.7
and new hardwood bark were somewhat adverse to the growth of seedling
roots, mostly because they contained large pieces of bark which often blocked
the penetration of roots. Also it is difficult to compact such coarse materials
very much and roots are apt to dry out more readily in them. In general,
root growth was best in all in the old barks. The only other material of
those tried that compared favorably with the bark was fine vermiculite,
tested for two kinds of seeds only.
Bark as a Rooting Medium for Cuttings
There is a continuing search for new and better media for rooting cuttings
of various sorts. Since bark, especially the old materials, might offer possi-
bilities here, a trial was made of old bark in comparison to sand. Beds in
the basement at the greenhouse, furnished with fluorescent light, were pre-
pared with the materials listed in Table 8. Concord grape cuttings were
placed in them for over a month in early spring. The results on a limited
number of cuttings show that old softwood bark, either alone or mixed
with sand, has distinctly advantageous possibilities as a rooting medium.
Table 8. Comparison of Bark Mixtures as Rooting Media for Grape Cuttings
Rooting Media Number Rooted Percent Rooted
1/2 Old softwood bark, % sand 29 80
Old softwood bark 25 69
Sand 19 52
V2 Old hardwood bark, V2 sand 18 50
Geranium cuttings rooted well in the two old barks mixed with sand, in
comparison to sand alone. However, the roots broke off more easily in the
sand-bark mixtures. This difficulty probably could be overcome by judicious
watering.
Effects of Bark Mulches on Greenhouse Rose Production
Cow manure is widely used as mulch for greenhouse roses. It is not too
readily available at times and waste bark seemed to offer some possibilities
as a substitute. Two ground-beds of soil, 14 feet by 4 feet, were each divided
in half, and each block prepared as follows: (a) received five 14-quart pails
full of old hardwood bark, (b) 5 pails of peat, (c) nothing, (d) 5 pails
old softwood bark. These additions were each mixed thoroughly with the
soil and the beds steam sterilized. Eight hundred grams of superphosphate
were then mixed with the contents of each block. Later, an equal number of
two varieties of budded rose plants, Hildegarde and Better Times, were
planted in the four blocks, 28 per block. Six hundred and eight grams of
ground limestone were worked into the soil of each block. Three weeks later
the following mulches were applied: block (a) a 3-4 inch layer of old
hardwood bark, block (b) 3-4 inches of new hardwood bark, block (c)
3-4 inches of fresh cow manure, and block (d) 3-4 inches of old softw^ood
bark.
During the course of the growth of these plants some trouble was ex-
perienced with black spot and insects but application of Fermate sprays and
appropriate insecticides adequately controlled these troubles.
On May 6, about two and one-half months after setting out the plants,
bloom started to appear. Two additional fertilizer applications were made
during the summer. Late in August additional manure had to be added
to block (c) because of the rapid breakdown of the mulch.
Careful records were taken of the yields of blooms, a summary of Avhich
appears in Table 9. These results show that both new or old bark makes an
Table 9. Yield of Roses with Bark and Manure Mulches
Mulch Treatment
Old Hard- New Hard- Old Soft-
wood Bark wood Bark wood Bark Manure
Total no. of blooms 676 673 610 558
Ave. length of stems in inches 16.5 18.7 18.0 17.1
excellent mulch for roses. There is no significant difference between the
total yields of 676 marketable roses for the old hardwood bark and 673
for the new hardwood bark, but the differences between these and 558 roses
for the manure is probably significant.
The various mulch treatments caused no appreciable differences in stem
lengths of the roses. All bark-mulched blocks produced stem lengths that
would be regarded as adequate in the rose trade.
From the standpoint of working with the mulch in the greenhouse, the
bark treatments, especially the new and old hardwood, are much easier
to keep free of weeds. Also they do not decompose as rapidly as manure
and thus do not need replacement as often.
There is a definite place for bark as a mulch in the rose industry. Corn
cobs (ground up), tobacco stalks, and manure are some of the mulches now
10
being used. The results of this experiment indicate that bark may well
serve as a substitute for manure in mulching roses. It would last longer
than many other materials.
Effect of Bark on Immunity of Apple to Scab
It had been suggested that apple trees grown all their lives in pure bark
might be immune to the fungous disease known as apple scab. To test this
hypothesis, ten crocks each of old hardwood bark, old softwood bark and
soil control were each planted with five apple seeds. After germination, the
seedlings were thinned to two per crock. Five grams of 5-10-10 fertilizer
were added to each crock three times during growth. When the plants were
about one foot high, they were artifically inoculated with the apple scab
organism. Later observations showed severe scab infection on all bark
grown plants and to the same extent as the soil controls. It is evident from
this that growing apples in bark does not confer immunity to scab.
A Comparison of Shredded Bark and Sphagnum Peat
As a Packing Material for Shipping Live Plants
The possibility of using waste bark as a material for keeping live plants
moist naturally suggests itself. The bark was shredded by a hammer mill
at the Brown Company plant in Berlin, New Hampshire. New bark was very
stringy in comparison to the old bark.
A study was made of the comparative moisture holding capacity of
shredded bark and peat. Each material was soaked over night in water.
Table 10. Moisture Retaining Power of Shredded Bark and Peat During Air-Drying
Weights
in G
rams
Old
Old
New
New
Sphagnum
Softwood
H
ardwood
Softwood
Hardwood
Date
Peat
Bark
Bark
Bark
Bark
7-7-52
1000
1000
1000
1000
1000
7-10
990
950
950
935
850
7-14
980
925
940
920
840
7-17
980
925
935
920
835
7-20
975
920
920
900
825
Successive Weights of Oven Dried (80°C)
Shredded Bark
7-7-52
7-8
7-10
7-14
400
400
400
400
236
250
299
319
148
182
277
298
146
180
275
297
Percent water absorbed,
dry wt. basis
174
122
45
34
11
They were then allowed to rest on a wire screen until gravitational water
had drained away. One thousand grams of each moist substance were then
used in a test of their power to retain water against air drying. Each mass
of moist material was wrapped in polyethylene film with a ruler protruding
from one end to simulate a plant stem and the possible loss of moisture
through this seal. The results given in the upper part of Table 10 show that
at the end of 13 days the peat retained more water than the bark. Also the
old bark retained more water than the new bark.
The four shredded barks were tested for water loss in an oven to deter-
mine differences in rate of v/ater loss at high temperature, also differences
in water holding capacity on this basis. For a sample, 400 grams of water-
soaked bark were used after drainage of gravitatural water. Samples were
placed on paper squares in an oven at 80° C. Periodic weights were taken for
one week, as presented in the lower part of Table 10. Thus it is shown the
old bark had a much greater water retaining capacity than the new.
To test the effects on survival of living plants, nine rose plants were
packed with each kind of bark and with peat. Polyethylene film was wrapped
around the packing material. After the plants had been wrapped for a week
and stored in a 60°F. greenhouse, observations were taken. For the first
ten days the shredded bark kept the plants as healthy looking as did the
peat. After the second week, the leaves of the old softwood treated roses
showed a very slight wilting. At the end of the third week the peat-wrapped
roses showed only a slight wilting while the old bark roses were quite wilted.
Those in new shredded bark showed slightly more wilting than those in
peat, but still looked vigorous. The above tests indicate that shredded bark
may be used to good advantage as a moisture-holding packing material for
shipping or storing live plants.
Part II Field Plots
In order to determine the possible use of waste bark for improving field
crop production, a field experiment was started on a plot of moderately
level land in Madbury, New Hampshire. The soil type was Bamstead fine
sandy loam and very uniform in texture. Soil samples showed an average
pH of 5.2 and nutrients were present only in traces or were entirely lacking.
The total area, 140 feet x 300 feet, was divided into 30 plots 20 feet x
70 feet each. The treatments for the different series were:
1. No organic matter (control).
2. Manure, 1.5 tons per plot.
3. Old softwood bark, 120 cu. ft. per plot.
4. New softwood bark, 120 cu. ft. per plot.
5. Old hardwood bark, 120 cu. ft. per plot.
6. New hardwood bark, 120 cu. ft. per plot.
Each treatment was replicated five times in a randomized block design.
Five different crops were grown, as follows: (a) potatoes, Yampa the
first year, and Kennebec the second year; (b) squash, Baby Blue; (c)
beans, Jacobs Cattle; (d) bachelor button, Centaurea cyanus; and (e)
12
zinnia, dahlia-flowered. One row of each of the crops was grown in each
plot, running lengthwise of the plots, to facilitate cultivation.
Prior to planting and to bark or manure application, the entire area was
plowed eight inches deep and harrowed thoroughly with a disk harrow.
The old bark and manure were then mixed into the soil with a Gravely
rotary plow. The new barks were left on the surface as a mulch. The de-
tails of planting and of fertilizer application will not be given here other
than to state that what was considered to be ample fertilizer was applied.
This was partly applied by machine placement at planting time and partly
as side dressing later on. Each plot received the same amount of fertilizer,
but considerably less fertilizer was applied to the rows of flower crops than
to the vegetables.
In the fall of 1951, after the first crop was harvested, the new bark treat-
ments were plowed under.
Cultivation during the growth of the crops was by hand hoeing, two men
working almost continuously.
There was some deer damage to the bean and squash plants during
growth, but an effort was made in presenting the harvest data to take that
into account. The summer of 1952 was very dry, so that some of the later
fertilizer applications were without effect.
Table 11. Yields of Crops Grown in Field Plots with Bark
Crops
Yields
for
Years
Old
Soft-
wood
Old
Hard-
wood
New
Soft-
wood
New
Hard-
wood
Control
Manure
Zinnia
1951
1952
totals
1951
1952
otals
1951
1952
Totals
1951
1952
Totals
1951
1952
Totals
588
2195
597
2035
532
1931
512
1893
566
1191
1612
2120
No. of blooms
Bachelor
button
2783
3705
11700
2632
2655
13362
2463
5774
11610
2405
7089
9891
1757
4295
8126
3732
14334
17216
No. of blooms t
Beans
lbs. of pods
15405
56.6
107.1
16017
66.0
86.5
17384
51.7
76.6
16980
54.2
69.8
12421
22.3
53.7
31550
97.2
103.8
Squash
lbs. of fruit
163.7
564.0
309.9
152.5
710.3
240.3
128.3
721.7
251.1
124.0
619.8
236.7
76.0
554.0
238.9
201.0
979.7
232.8
Potatoes
lbs. of tubers
873.9
538
436
950.6
548
446
972.8
436
433
856.5
448
428
792.9
474
423
1212.5
531
564
974
994
869
876
897
1095
13
The total yield data for the different crops for each year and for both
years together are summarized in Table 11. The totals for both years are
shown graphically in Figure 1 in the order of size of yields for ready com-
parison.
Discussion of Field Plot Results
The zinnia harvest for the first year shows the manure plots to be the
heaviest producers of flowers. The following year, the best yield was obtained
with the old softwood bark, closely followed by manure and old hardwood.
It should be noted, however, that all of the bark mixtures were ahead of
the control in total production in 1952.
The bachelor button harvest for the first year showed the manure plots
superior to all others. In the second year the manure was still the best
medium, but the old softwood and hardwood bark mixtures were improved
over 1951. There was better production the second year in the new bark
plots when this material was plowed under than in the first year when it
was used as a surface mulch.
The bark plots were probably starting to show some of the residual
effects of the organic matter in the soil as reflected in the higher flower
production in 1952 than in 1951. The new bark, when used as a mulch or
plowed under, produced higher yields than the control. The high yields
from the manure plots in both years shows that this is a satisfactory treat-
ment for bachelor button production.
The bean harvest data show that the manure-treated plots yielded more
than any other treatment in 1951. Statistical analysis could not be applied
to the bean crop results because of the heavy deer damage. The results for
1952 compared to 1951, show that, as with the zinnias, the increase in yield
in the old softwood bark plots was equal to that of the manure plots.
The Baby Blue squash yield in 1951 showed the manure plots again ahead
of the other plots by a significant amount. The new bark plot yields indi-
cate greater benefit from these when used as a mulch than when plowed
under. In 1951 the manure plot yield was the only one significantly greater
than controls at the 5 percent level. For 1952, when the yields for deer
damaged plots are omitted, as presented here, the yields from the old soft-
wood bark were outstandingly high. The others were close to the control.
With the potato crop in 1951, the yields for manure, old hardwood, and
old softwood treatments were significantly greater than the controls at
the 5 percent level. In 1952, the manure plot yield was the only one sig-
nificantly greater.
In general the total yield data for all five crops, as shown in Figure 1.
present two outstanding features. First, it is very obvious that the best yield
for all crops was obtained with manure. This would be expected, for manure
not only improves the physical qualities of soil, but also adds a consider-
able amount of plant nutrients beyond those supplied by the regular fer-
tilizer treatments. It is well recognized that bark would add scarcely any
of these elements. The other noteworthy feature is that all four of the bark
treatments gave greater total yields than the control with all crops except
the potato. This indicates that bark has some potentialities as a soil improver.
14
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TREATMENT
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Figure 1. Yields of flowers and vege-
tables tested in field plots. Upper left,
zinnias; upper right, beans; middle
left, potato tubers; middle right,
squash; lower right, bachelor buttons.
3Cp00
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TREATMENT
15
Summary
This is a report on experiments to determine the possible value of waste
bark as a soil improver. The bark was used in greenhouse cultures with
plants and in field plot tests.
In the greenhouse, the effect of bark on plant growth was tested both in
mixtures with soil and in the pure state. Both pot and bed cultures were
employed. Usually it was compared with soil alone as control cultures, and
often with peat under similar conditions. The greenhouse experiments com-
prise nine sets of cultures, and one of tests of water holding capacity,
1. A set of pot cultures designed to show the effects on plant growth of
varying proportions of bark to soil, and peat to soil, showed that low con-
centrations of these organic substances gave better yields than higher ones.
Older bark gave higher yields than fresh ones and peat for the first crop
(cabbage) and significantly higher yields than soil controls. However, ad-
vantages for these additives tended to disappear with successive crops
(radish and corn), probably due to decay of the organic matter.
2. Flower yields of two ornamentals were tested in greenhouse bench
cultures with (a) old bark-soil mixture, (b) peat-soil, and (c) soil only.
With snapdragons the yield was best in bark and next best in peat. Carna-
tions yielded best in the peat mixture. However, none of the differences
were very great, probably due to high compost content of the original soil.
3. Old bark, undiluted with soil but with added fertilizer, was compared
with other wood wastes and soil as growing media for cabbage and barley.
Yields for both in bark was significantly greater than in soil.
4. Even old bark will not increase yields of plants in bark-soil mixtures
above that of soil controls, unless fertilizer is added. This was demonstrated
by growing wax beans in a one-to-two ratio of bark to soil, with no fertilizer.
The yield from soil-grown plants was significantly greater.
5. The statements in 3 and 4 above were further substantiated by results
with tomatoes grown in pure old bark in comparison with pure peat and
soil. Each was liberally fertilized. The crop in peat was a total failure. Total
yields of fruit, as well as size of fruit, was greater in the bark than in soil
by a very wide margin.
6. Pot cultures of cabbage were grown in mixtures of old bark and
sewage sludge (no added fertilizer), in comparison to soil. The old hardwood
bark-sewage mixtures produced significantly better growth than did soil.
Yields in those of old softwood bark were close to yields of the controls.
7. The root growth of three kinds of seedlings in the four kinds of
bark was compared with root growth in other kinds of media, such as sand.
Growth was best in old bark, but that in vermiculite was about as good
for two kinds of seedlings.
'O"
8. Tests of old bark, alone and mixed with sand, as rooting media for
grape cuttings showed that these media have good possibilities for such use.
Bark was also satisfactory for rooting geranium.
16
9. Used as a mulch for growing greenhouse roses, bark showed outstand-
ing possibilities. Yields of rose blooms were considerably greater with two
bark mulches than when mulched with cow manure. The bark also lasted
lonaer than manure.
f
10. Bark as a growing medium for apple seedlings had no influence on
infection from scab. This was contrary to a supposition that it might cause
immunity.
11. Shredded bark compared very favorably with sphagnum peat as a
packing material for live plants.
For field plot trials, the four kinds of bark, in comparison to manure and
controls without organic matter, were applied in replicated plots. All were
fertilized alike. As might be expected from the additional fertility it con-
tained (beyond the commercial fertilizer application), manure produced
best yields for all five crops tested. However, plants grown in the two kinds
of old bark produced considerably higher yields than those in the soil
controls in 8 out of a possible 10 cases. Even the new barks gave higher
yields than controls with all crops except potatoes. When it is considered
that the original soil was practically devoid of nutrients, this shows that
bark has considerable potentialities as a soil builder in field use.
Literature Cited
1. Baker, J. R., and Dunn, S. Sawdust Composts in Soil Improvement: III.
Pot Culture Studies with Composts from (a) Outdoor Pits (b)
Wooden Bins with High Moisture, (c) Other Mixtures. Plant and
Soil 6:113-128. 1955.
2. Composting for Disposal of Organic Refuse, and Biblography. Techn.
Bui. 1 and 2, Institute of Eng. Res., Univ. of Calif., 1950.
3. Dunn, S., Wolfe, L. P. Jr., MacDonald, W. A., and Baker, J. R.
Field Plot Studies with Sawdust for Soil Improvement. Plant and
Soil 4:164-170. 1952.
4. MacDonald, W. A., and Dunn, S. Sawdust Composts in Soil Improve-
ment: II. Pot Cultures with Compost Mixtures of Sawdust and
Manure, Steam Treated Composts and Miscellaneous Mixtures.
Plant and Soil 4:235-247. 1953,
5. Northeastern Wood Utilization Council Inc., The Chemistry and Utili-
zation of Bark. Bulletin 25. 1949.
6. Rettie, J. C, AND Simmons, F. C. Estimates of Bark Supply in the
Northeast. In Northeastern Wood Utilization Council Bui. 25:7-18.
1949.
7. Wolfe, L. P. Jr., and Dunn, S. Sawdust Composts in Soil Improvement:
I. Studies on Aeration, Acid Hydrolysis, Manure and Waste Ma-
terials as Composting Aids. Plant and Soil 4:223-234. 1953.
17
SUPPLEMENT
The Comparative Value of Bark as a
Surface Mulch for Apples, Blueberries,
and Raspberries
By L. PHELPS LATIMER
Associate Horticulturist
New Hampshire Agricultural Experiment Station
Apples
IT is standard orchard practice in the New England states to grow apple
trees under a sod-mulch system, placing additional hay or other suitable
mulching materials on the ground beneath the spread of the branches of
the trees in order to control weed growth, improve the physical condition
of the soil, conserve moisture, and supply mineral nutrients. Cultivation is
thus eliminated. Hay has been considered the best material for this purpose.
The purpose of this experiment was to determine the value of bark com-
pared to hay as a mulching material in the orchard. Three separate blocks
of trees were utilized, and the tests were started in the autumn of 1950
as follows:
1. 32 five-year-old Mcintosh at Durham.
2. 25 seven-year-old Mcintosh at Durham.
3. 120 three-year-old Virginia Crab and Robusta No. 5 apple
stocks at West Stewartstown.
In the experiment at Durham, old softwood bark was compared with hay
as mulch; at West Stewartstown, old softwood bark and new softwood bark
were compared with hay as mulch. The criteria for measuring the response
to different mulches were annual twig growth in all blocks and, in addition,
yield of fruit in Block 1 (at Durham).
Since the difference in twig growth between treatments was not stastically
significant at the 5 percent level, the data taken at Durham indicate that
the bark-mulched trees compared favorably with hay-mulched trees in termi-
nal growth. At West Stewartstown there seemed to be a tendency for hay-
mulched trees to make slightly greater terminal growth than those mulched
with either new or old softwood bark. On the other hand, trees mulched
with old softwood bark made growth equal to that produced by trees mulched
with new softwood bark.
18
Results comparing yields are not conclusive; first, because the trees were
only bearing their first small crops, and second, because mulch placed
around the trees in the fall of 1950 could not possibly have had an effect
on fruit bud formation until the summer of 1951, and consequently on the
fruit crop of 1952. Further observations are needed for definite conclusions.
Blueberries
On October 16, 1950, plots were set up on the Chandler Farm in Dover
to compare the effects of new hardwood bark, old softwood bark, sawdust,
and hay on annual shoot growth of blueberries. The growth made by plants
mulched with new hardwood bark as well as by those mulched with hay
was significantly greater at the 1 percent level than the growth made by
plants mulched with old softwood bark, and was significantly greater at
the 5 percent level than growth made by plants mulched with sawdust. The
fact that the least growth was made by blueberry plants mulched with old
softwood bark may be reflected in the fact that there was less soil nitrate
nitrogen beneath the old softwood bark than under the new hardwood-bark
mulch. One apparent advantage of the bark mulches is that these materials
are free from the seeds of obnoxious weeds.
At the Smith Farm in Gilford, three-year-old blueberry plants were mulched
in the fall of 1950, some with old hardwood bark, and some with hay. A
control row was kept in clean cultivation. In the winter of 1950-51, heavy
snow broke down the blueberry plants to the ground. The hay-mulched and
clean-cultivated plants did not recover, whereas the plants mulched with
old hardwood bark did recover and performed Avell subsequently. The bark
mulch appeared to be superior to any other for blueberries. It was very easy
to work and to keep free of witch grass and other weeds.
Raspberries
Four 150-foot rows of Durham fall-bearing raspberries at the University
Horticultural Farm were used for this experiment. One row was kept in
cultivation, one mulched with hay, one with sawdust and one with old
softwood bark. The results showed that the cultivated row outyielded the
rows under mulch treatments.
The bark-mulched row, however, produced more fruit than the hay or
sawdust-mulched rows. The largest sized berries were produced on plants
mulched with either sawdust or hay. This probably was the result of lower
yield under these treatments. More sucker plants were produced in the
bark-mulched row than in the other rows. This might be an advantage to
the commercial nurseryman.
19
630.72
N532
no. 426-450
DATE DUE
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