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Wetting properties of dried-out nursery container media
Scientia Horticulturae, 17 (1982) 49--59
49
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
WETTING PROPERTIES OF DRIED-OUT NURSERY CONTAINER MEDIA
D.V. BEARDSELL and D.G. NICHOLS
Horticultural Research Institute, Knoxfield, P.O. Box 174, Ferntree Gully, Vic. 3156 (Australia) (Accepted for publication 22 July 1981)
ABSTRACT Beardsell, D.V. and Nichols, D.G., 1982. Wetting properties of dried-out nursery container media. Scientia Hortic., 17: 49--59. Container mixes consisting of Pinus radiata bark and brown coal or clay loam soil have poor wetting properties when they are dry, because of the shrinkage of all three and the hydrophobic nature of dry pinebark. The wettability of coarse sand, which is independent of its dryness, is quantitatively transferred to container mixes in proportion to the a m o u n t used.
INTRODUCTION
Container media containing pinebark, if watered on a regular basis, have good waterholding properties and have been found to be satisfactory for growing a wide range of plants (Beardsell et al., 1979a,b). However, in commercial nursery practice, container media often dry out and become difficult to re-wet, especially media containing pinebark (Airhart et al., 1978; Solbraa, 1979; Gehring and Lewis, 1980). This work was designed, firstly to determine the wetting properties of various media, and secondly, to determine ways of improving the wettability of mixes containing pinebark. MATERIALS AND METHODS M e d i a c o n s t i t u e n t s . - - The wetting properties of pinebark (from P i n u s radiata), coarse sand, brown coal, clay loam soil and sandy loam soil
(mechanical analysis in Table I) were determined by drying the saturated media in a laboratory in ten 10 X 10 cm containers for 0, 6, 12, 24, 48 and 96 days. The containers of media were weighed and then wetted with 300 ml of water administered by a fine sprinkler and drained in a humid environment for 24 h. Previous tests showed that this was more than enough water
0304-4238/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
5O TABLE I Particle size distribution of container materials, expressed as a percentage of total volume. Data are the averages of 5 replications Particle size Pinebark Coarse (ram) sand
Brown coal
Clay loam
Sandy loam
>3.5 >2.6 >2.0 >1.5 >1.0 >0.5 <0.5 L.S.D. 5% 1%
34.3 13.5 12.6 11.9 11.2 11.4 5.1
36.0 25.3 15.6 9.1 6.1 6.0 1.8
39.4 8.7 7.5 7.7 7.8 16.2 12.5
0.3 0.4 3.0 7.1 13.4 29.5 46.3
0.1 0.3 0.8 2.3 8.5 37.3 50.6
3.0 4.1
2.6 3.4
2.3 3.1
3.0 4.1
3.5 4.7
to saturate all of the media. The containers were then re-weighed, and oven dried at 65°C to determine moisture content. Moisture content is expressed as percentage of initial container capacity (White and Mastalerz, 1966). The drainage holes were covered with filter paper to prevent washing fine particles o u t of the media. Shrinkage, namely the distance between the top of the dry potting media and the side of the pot, was measured at 4 places with calipers, and the mean was recorded. To separate the wetting properties of air-dried pinebark and brown coal from their shrinkage properties, 80 cm 3 of each was placed into 5 small containers (5 cm × 7 cm), which were tapped gently to settle the contents and prevent any continuous gap at the sides. T w e n t y ml of water was added to the t o p of the media, where the h y d r o p h o b i c nature of both pinebark and brown coal prevented rapid infiltration. After 24 h of infiltration and draining, the media were oven-dried in the containers at 65°C to determine h o w much water was retained. M e d i a c o m b i n a t i o n s . - - In order to determine h o w the wetting properties of
container mixes were influenced by ingredients which have different wetting properties, the above procedure was repeated using the following m~dia combinations by volume: pinebark : coarse sand 2:1, 1:1, 1:2 pinebark : brown coal 2:1, 1:1, 1:2 pinebark : coarse sand : brown coal 2:1:1, 4:1:1 pinebark : coarse sand : clay loam 2:1:1 Because of the large n u m b e r of media in this experiment, the number of replications was reduced to 5, and sampling was carried out on Days 0, 4, 8, 16 and 32.
51
12()
......................
10(
:._.
~ 40
20
10
8o
40
DAYS OF DRYING
"'t
~ol ~ . . ~ ~ | ~ - -
S
~---,~.,
~1 \ ~ ' ~ ~ ~ , . , . ~ i ,ol ~~~-~~~.:"" t
R2C
i
4
8
16 DAYS OF DRYING
3'2
Fig. 1. (a) The effect of drying-time on the wettability of coarse sand (u), sandy loam (T), clay loam (A), brown coal (o) and pinebark (o). (b) The effect of drying-time on the wettability of container media, coarse sand (S), clay loam (L), brown coal (C) and pinebark (P). The mixtures are in the ratios shown, e.g. 2 P.S.L. represents the media 2 parts pinebark:l part coarse sand:l part clay loam.
52 RESULTS AND DISCUSSION constituents. - - The wettability of coarse sand was unaffected by drying (Figs. l a and 2), containers of coarse sand actually increase in waterholding capacity with subsequent watering, as some fine particles are washed down after the first watering, thus reducing drainage (percentage water held at re-wetting compared with initial container capacity greater than 100). This effect has also been observed for scoria (Beardsell et al., 1979a). While Fig. 1 shows the effect of the drying-time on the wettability of the media, the results are more clearly shown in Fig. 2, where wettability is compared to the moisture content of the media. For coarse sand, the relationship between moisture content and wettability is linear (Table V, Fig. 2) but not significant, and this, together with the very small slope of the line, shows that the wettability of coarse sand is unaffected by its moisture content. Coarse sand does n o t shrink (Table II) and is not hydrophobic when dry. Figure 2 shows that sandy loam also has good re-wetting properties (70% when dry), but its relationship is curvilinear and highly significant (Table V) and since it does n o t shrink it must be slightly hydrophobic when dry (Table II). Brown coal, however, has a wettability which is proportional to its dryness (Table V, Fig. 2) and shrinkage properties (Fig. 3). Table III shows
Media
I',:
.
.
#,, 1-
80
1-
40
20 PERCENT
40
6O
8O
INITIAL CONTAINER CAPACITY
Fig. 2. The effect of water content on the wettability of coarse sand (e), sandy loam (V), clay loam (A), brown coal (o) and pinebark (v).
53 TABLE II Shrinkage of container media. The shrinkage measured was the distance between the dry medium and the side of the container Medium
Days of drying
Initial container capacity
Shrinkage (mm)
0.0 0.0 7.7 7.6 3.4 0.8 7.0 3.2 3.0 3.0 2.8 6.8 5.8 8.0 5.0 5.3 6.0
0.0 0.0 2.9 3.6 2.5 0.0 4.6 1.6 1.0 0.6 0.3 2.8 2.8 3.6 1.0 1.4 1.8
1.5 I.I 2.6 2.0
0.5 0.4 0.8 0.6
(~) Coarse sand Sandy loam Clay loam Brown coal Pinebark Coarse sand Brown coal Pinebark 2 pinebark:l coarse sand 1 pinebark:l coarse sand 1 pinebark:2 coarse sand 2 pinebark:l brown coal 1 pinebark:l brown coal 1 pinebark:2 brown coal 2 pinebark:l brown coal:l coarse sand 2 pinebark: 1 clay loam: 1 coarse sand 4 pinebark:l brown coal:l coarse sand L.S.D. L.S.D.
1% 5% 1% 5%
96 96 96 96 96 32 32 32 32 32 32 32 32 32 32 32 32
96 day figures 32 day figures
TABLE III Percent water retention of pre-shrunk, air-dried pinebark and brown coal. This table illustrates the hydrophobic nature of pinebark and brown coal after minimising the effects of shrinkage Material
Wetting (%)
Pinebark
18
Brown coal
59
L.S.D. 5%
L.S.D. 1%
6.2
8.9
that, after minimising the effects of shrinkage, brown coal shows hydrop h o b i c p r o p e r t i e s w h e n d r y , a b s o r b i n g 59% o f 20 m l a d d e d t o t h e t o p o f t h e m e d i u m . S i n c e t h e w e t t a b i l i t y o f b r o w n c o a l is i n v e r s e l y r e l a t e d t o its d r y n e s s ( F i g . 2), i t w o u l d a p p e a r , h o w e v e r , t h a t s h r i n k a g e is t h e d o m i n a n t f a c t o r in its p o o r r e - w e t t i n g p r o p e r t i e s .
54
100 >-
80
i
,z 40 o e~
20
i
2
3 SHRINKAGE
Fig. 3. T h e
4
5
(mm)
shrinkage (X) and wettability (Y) of clay loam (A), brown coal (*), Y = 9 6 . 0 - - 1 8 . 0 X + 2 . 2 X 2 , r -- 0.85**; pinebark (D), Y = 96.4 -- 37.2X + 12.7X2 , r = 0.74**. Y = 106.9
relationship
-- 21.9X
between
+ 1.6X
2 , r = 0.88**;
The wettability of the pinebark also declined as it dried out, b u t the relationship was n o t linear (Table V, Fig. 2). Since pinebark shrinks very little (Table II), its poor wettability when dry appears related to its hydrophobic properties which increase with drying, giving rise to the curvilinear relationship shown in Fig. 2. Table III shows that when the effects of shrink. age are minimised, dry pinebark is 3 times more h y d r o p h o b i c than brown coal. Water added to dry pinebark mostly runs over the surface and down the sides of the container with little penetration into the medium itself. The wettability of the clay loam soil decreased as it dried out, b u t in contrast to pinebark, the rate of reduction in wettability decreased as this medium dried o u t (Table V, Fig. 2). The curvilinear relationship between wetting and shrinkage of clay loam (Figs. 2 and 3) must be due to some offsetting of the shrinkage effects by increased hydrophilic properties of the material when it is dry, otherwise the relationship would be linear like that for brown coal. Pinebark, brown coal and clay loam all have poor wetting properties if they dry o u t in a p o t (FIT. 2). P i n e b a r k and b r o w n coal c o m b i n a t i o n s . -- The wetting properties of dry
pinebark and brown coal container mixtures, especially the mixture of 1 pinebark: 2 brown coal, were inferior to those of the individual materials (Fig. 4a and Table III). This could be the result of excessive shrinkage of brown coal combined with the h y d r o p h o b i c nature of dry pinebark, the interaction causing the water to run over the t o p of the dry mixture and down the space between the mixture and the side of the container. Such mixes are difficult t o wet when dry, holding only a third of the original
A J . l ' l l S V l J 3M-31:1
IN3~)U3d
>. F-,
U m W
o~
I,-
iz
'~P'Z 0
o
•
% •
•
toni
\ co
)
o
o
°/i
o oo~oo~.
A I nlSVIJ.~W-
31:1
J.N3~l:~3d
0
).
,( U
_z
m 6d
U
_z
56 (c)
>,
s_ p-
8O
lO
~o PERCENT
80
INITIAL CONTAINER CAPACITY
Fig. 4. (a) The effect of water content on the wettability of brown coal (e), pinebark (c), 2 p i n e b a r k : l brown coal (A), pinebark:brown coal (T) and pin•bark:2 brown coal (=). (b) The effect of water content on the wettability of coarse sand (•), pinebark (=), pinebark:2 coarse sand (o), pin•bark:coarse sand (V) and 2 pin•bark:coarse sand (A). (c) The effect of water content on the wettability of pin•bark-based container mixtures; 2 pin•bark: 1 coarse sand (•), 2 p i n e b a r k : l brown coal (A), 2 p i n e b a r k : l brown coal:l coarse sand (•), 2 p i n e b a r k : l clay l o a m : l coarse sand (V), 4 p i n e b a r k : l brown coal:l coarse sand (o). Percentage by volume of coarse sand is indicated in parentheses.
TABLE IV Percentage of initial container capacity obtained from a single watering after 8 days of drying. Values with the. same subscript are not significantly different, which shows that mixtures of pinebark and brown coal have poorer wetting properties than the materials themselves Media
Re-wettability
Pinebark 2 P i n e b a r k : l brown coal 1 P i n e b a r k : l brown coal 1 Pinebark:2 brown coal Brown coal
83.5 65.1 68.3 55.9 76.2
L.S.D.
7.8 10.4
(%)
5% 1%
a b b c a
96 96 96 96 96 32 32 32 32 32 32 32 32 32 32 32 32
Coarse sand Sandy loam Clay l o a m B r o w n coal Pinebark Coarse sand B r o w n coal Pinebark 2 pinebark:l 1 pinebark:l 1 pinebark:2 2 pinebark:l 1 pinebark:l 1 pinebark:2 2 pinebark:l 2 pinebark:l 4 pinebark:l coarse sand coarse sand coarse sand b r o w n coal b r o w n coal b r o w n coal brown coal:l coarse sand clay l o a m : l coarse sand brown coal:l coarse sand
Days of drying
Medium
Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y
= = = = = = = = = = = = = = =
Y = 69.4
+ 0.56X
--
0.0046X 2 43.3 -- 0.033X + 0.0071X 2 48.0 + 0.64X 32.6 + 1 . 5 9 X - - 0 . 0 1 0 X 2 174.0 + 0.16X 60.7 + 0 . 6 4 X 34.4 + 2.05X-- 0.15X 2 81.1 + 0.86X- 0.0067X 2 79.2 + 0.97X -- 0.094X 2 96.1 + 0.54X 22.0 + 2.05X- 0.12X 2 44.7 + 0 . 9 0 X 28.0 + 0.90X 63.0 + 1.22X-- 0.065X 2 62.6 -- 0.28X + 0.09X 2 56.5 + 1 . 4 2 X - - 0.91X 2
Y = 115.8 + 0.29X
Equation
0.13 0.87 0.88 0.85 0.96 0.12 0.81 0.94 0.77 0.90 0.84 0.98 0.96 0.96 0.95 0.84 0.94
Regression coefficient
N.S. 1 1 1 1 N.S. 1 1 1 1 1 1 1 1 1 1 1
Significance (%)
R e l a t i o n s h i p s b e t w e e n m o i s t u r e c o n t e n t ( X ) a n d w e t t a b i l i t y (Y). M o i s t u r e c o n t e n t (X) a n d r e - w e t t a b i l i t y ( Y ) are e x p r e s s e d as p e r c e n t a g e o f initial c o n t a i n e r c a p a c i t y ( W h i t e a n d M a s t a l e r z , 1 9 6 6 )
TABLE V
CJ I
58 container capacity (Fig. 4a). Since we have previously shown pinebark/ brown coal mixtures to have good water relations if they are not allowed to dry out (Beardsell et al., 1979b), the re-wetting difficulties are simply avoided if the mixtures are prevented from drying out during nursery production. As in the first experiment (see Fig. 2), the wettability of brown coal was directly related to moisture content and pinebark had decreasing wettability with drying (Fig. 4a). The wettabilities of the 1:2 and 1:1 pinebark/ brown coal mixtures were also directly related to moisture content and were thus largely influenced by the brown coal, whereas the moisture content of 2 pinebark: 1 brown coal had a curvilinear relationship with wettability, largely influenced by the pinebark. Figure 4a and Table IV clearly show that 1:2 and 2:1 mixtures of pinebark and brown coal had very poor re-wetting properties as they dried out. and coarse sand combinations. - - Figures 2, 4b and 4c show that the superior wetting-properties of coarse sand are transferred to mixtures with pinebark in proportion to the amount of coarse sand used. To achieve acceptable levels of wettability when dry (> 80% of initial container capacity), media need to contain at least 30% by volume of coarse sand. In the media 2:1:1 pinebark:coarse sand:brown coal (25% sand) and 4:1:1 pinebark:coarse sand:brown coal (17% sand), re-wettability after complete drying out decreased to only 60% of the initial container capacity. Figure 4c shows that when clay loam was substituted for brown coal (comparing 2:1:1 pinebark:coarse sand:clay loam with 2:1:1 pinebark:coarse sand: brown coal), mixture properties were dominated b y the clay loam (see Fig. 2), and wettability decreased rapidly in the early stages because of shrinkage of the media but levelled off to approximately 60% initial container capacity. The direct effect of incorporating coarse sand into dried-out pinebark/brown coal mixtures is evidenced by the 20% re-wetting of 2 pinebark: 1 brown coal compared to 60% re-wetting of 2 pinebark: 1 brown coal:l coarse sand after both have completely dried out (Fig. 4c). This dramatically illustrates the benefit of incorporating a material which has good wetting-properties when dry into a container mixture. Although earlier work (Beardsell et al., 1979b) showed that coarse sand had a very low water-holding capacity, it is an important component in container mixtures which are liable to dry out, because it aids water penetration. Increasing the amount of sand in a mix from 17 to 30% by volume does, however, reduce the available water-holding capacity by approximately 17% (estimated from Beardsell et al., 1979b) and increases the weight of the mixture also by 17% {from the dry weights of the media used in this experiment). Thus, it is better nursery practice to prevent container media from drying out rather than to add coarse sand.
Pinebark
59 ACKNOWLEDGEMENTS We w o u l d like t o t h a n k Messrs. R. J a r d i n e a n d D. Richards for statistical analysis, a n d Miss D. F o n t a n a f o r technical assistance.
REFERENCES Airhart, D.L., Natarella, N.J. and Pokorny, F.A., 1978. Influence of initial moisture content on wettability of a milled pinebark medium. HortScience, 13: 432--434. Beardsell, D.V., Nichols, D.G. and Jones, D.L., 1979a. Physical properties of nursery potting mixtures. Scientia Hortic., 11: 1--8. Beardsell, D.V., Nichols, D.G. and Jones, D.L., 1979b. Water relations of nursery potting media. Scientia Hortic., 11: 9--17. Gehring, J.M. and Lewis, A.J., 1980. Effect of hydrogel on wilting and moisture stress of bedding plants. J. Am. Soc. Hortic. Sci., 105: 511--513. Solbraa, K., 1979. Composting of bark. I. Different bark qualities and their uses in plant production. Medd. Nor. Inst. Skogforsoeksves., 34: 281--333. White, J.W. and Mastalerz, J.W., 1966. Soil moisture as related to container capacity. J. Am. Soc. Hortic. Sci., 89: 758--765.
49
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
WETTING PROPERTIES OF DRIED-OUT NURSERY CONTAINER MEDIA
D.V. BEARDSELL and D.G. NICHOLS
Horticultural Research Institute, Knoxfield, P.O. Box 174, Ferntree Gully, Vic. 3156 (Australia) (Accepted for publication 22 July 1981)
ABSTRACT Beardsell, D.V. and Nichols, D.G., 1982. Wetting properties of dried-out nursery container media. Scientia Hortic., 17: 49--59. Container mixes consisting of Pinus radiata bark and brown coal or clay loam soil have poor wetting properties when they are dry, because of the shrinkage of all three and the hydrophobic nature of dry pinebark. The wettability of coarse sand, which is independent of its dryness, is quantitatively transferred to container mixes in proportion to the a m o u n t used.
INTRODUCTION
Container media containing pinebark, if watered on a regular basis, have good waterholding properties and have been found to be satisfactory for growing a wide range of plants (Beardsell et al., 1979a,b). However, in commercial nursery practice, container media often dry out and become difficult to re-wet, especially media containing pinebark (Airhart et al., 1978; Solbraa, 1979; Gehring and Lewis, 1980). This work was designed, firstly to determine the wetting properties of various media, and secondly, to determine ways of improving the wettability of mixes containing pinebark. MATERIALS AND METHODS M e d i a c o n s t i t u e n t s . - - The wetting properties of pinebark (from P i n u s radiata), coarse sand, brown coal, clay loam soil and sandy loam soil
(mechanical analysis in Table I) were determined by drying the saturated media in a laboratory in ten 10 X 10 cm containers for 0, 6, 12, 24, 48 and 96 days. The containers of media were weighed and then wetted with 300 ml of water administered by a fine sprinkler and drained in a humid environment for 24 h. Previous tests showed that this was more than enough water
0304-4238/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
5O TABLE I Particle size distribution of container materials, expressed as a percentage of total volume. Data are the averages of 5 replications Particle size Pinebark Coarse (ram) sand
Brown coal
Clay loam
Sandy loam
>3.5 >2.6 >2.0 >1.5 >1.0 >0.5 <0.5 L.S.D. 5% 1%
34.3 13.5 12.6 11.9 11.2 11.4 5.1
36.0 25.3 15.6 9.1 6.1 6.0 1.8
39.4 8.7 7.5 7.7 7.8 16.2 12.5
0.3 0.4 3.0 7.1 13.4 29.5 46.3
0.1 0.3 0.8 2.3 8.5 37.3 50.6
3.0 4.1
2.6 3.4
2.3 3.1
3.0 4.1
3.5 4.7
to saturate all of the media. The containers were then re-weighed, and oven dried at 65°C to determine moisture content. Moisture content is expressed as percentage of initial container capacity (White and Mastalerz, 1966). The drainage holes were covered with filter paper to prevent washing fine particles o u t of the media. Shrinkage, namely the distance between the top of the dry potting media and the side of the pot, was measured at 4 places with calipers, and the mean was recorded. To separate the wetting properties of air-dried pinebark and brown coal from their shrinkage properties, 80 cm 3 of each was placed into 5 small containers (5 cm × 7 cm), which were tapped gently to settle the contents and prevent any continuous gap at the sides. T w e n t y ml of water was added to the t o p of the media, where the h y d r o p h o b i c nature of both pinebark and brown coal prevented rapid infiltration. After 24 h of infiltration and draining, the media were oven-dried in the containers at 65°C to determine h o w much water was retained. M e d i a c o m b i n a t i o n s . - - In order to determine h o w the wetting properties of
container mixes were influenced by ingredients which have different wetting properties, the above procedure was repeated using the following m~dia combinations by volume: pinebark : coarse sand 2:1, 1:1, 1:2 pinebark : brown coal 2:1, 1:1, 1:2 pinebark : coarse sand : brown coal 2:1:1, 4:1:1 pinebark : coarse sand : clay loam 2:1:1 Because of the large n u m b e r of media in this experiment, the number of replications was reduced to 5, and sampling was carried out on Days 0, 4, 8, 16 and 32.
51
12()
......................
10(
:._.
~ 40
20
10
8o
40
DAYS OF DRYING
"'t
~ol ~ . . ~ ~ | ~ - -
S
~---,~.,
~1 \ ~ ' ~ ~ ~ , . , . ~ i ,ol ~~~-~~~.:"" t
R2C
i
4
8
16 DAYS OF DRYING
3'2
Fig. 1. (a) The effect of drying-time on the wettability of coarse sand (u), sandy loam (T), clay loam (A), brown coal (o) and pinebark (o). (b) The effect of drying-time on the wettability of container media, coarse sand (S), clay loam (L), brown coal (C) and pinebark (P). The mixtures are in the ratios shown, e.g. 2 P.S.L. represents the media 2 parts pinebark:l part coarse sand:l part clay loam.
52 RESULTS AND DISCUSSION constituents. - - The wettability of coarse sand was unaffected by drying (Figs. l a and 2), containers of coarse sand actually increase in waterholding capacity with subsequent watering, as some fine particles are washed down after the first watering, thus reducing drainage (percentage water held at re-wetting compared with initial container capacity greater than 100). This effect has also been observed for scoria (Beardsell et al., 1979a). While Fig. 1 shows the effect of the drying-time on the wettability of the media, the results are more clearly shown in Fig. 2, where wettability is compared to the moisture content of the media. For coarse sand, the relationship between moisture content and wettability is linear (Table V, Fig. 2) but not significant, and this, together with the very small slope of the line, shows that the wettability of coarse sand is unaffected by its moisture content. Coarse sand does n o t shrink (Table II) and is not hydrophobic when dry. Figure 2 shows that sandy loam also has good re-wetting properties (70% when dry), but its relationship is curvilinear and highly significant (Table V) and since it does n o t shrink it must be slightly hydrophobic when dry (Table II). Brown coal, however, has a wettability which is proportional to its dryness (Table V, Fig. 2) and shrinkage properties (Fig. 3). Table III shows
Media
I',:
.
.
#,, 1-
80
1-
40
20 PERCENT
40
6O
8O
INITIAL CONTAINER CAPACITY
Fig. 2. The effect of water content on the wettability of coarse sand (e), sandy loam (V), clay loam (A), brown coal (o) and pinebark (v).
53 TABLE II Shrinkage of container media. The shrinkage measured was the distance between the dry medium and the side of the container Medium
Days of drying
Initial container capacity
Shrinkage (mm)
0.0 0.0 7.7 7.6 3.4 0.8 7.0 3.2 3.0 3.0 2.8 6.8 5.8 8.0 5.0 5.3 6.0
0.0 0.0 2.9 3.6 2.5 0.0 4.6 1.6 1.0 0.6 0.3 2.8 2.8 3.6 1.0 1.4 1.8
1.5 I.I 2.6 2.0
0.5 0.4 0.8 0.6
(~) Coarse sand Sandy loam Clay loam Brown coal Pinebark Coarse sand Brown coal Pinebark 2 pinebark:l coarse sand 1 pinebark:l coarse sand 1 pinebark:2 coarse sand 2 pinebark:l brown coal 1 pinebark:l brown coal 1 pinebark:2 brown coal 2 pinebark:l brown coal:l coarse sand 2 pinebark: 1 clay loam: 1 coarse sand 4 pinebark:l brown coal:l coarse sand L.S.D. L.S.D.
1% 5% 1% 5%
96 96 96 96 96 32 32 32 32 32 32 32 32 32 32 32 32
96 day figures 32 day figures
TABLE III Percent water retention of pre-shrunk, air-dried pinebark and brown coal. This table illustrates the hydrophobic nature of pinebark and brown coal after minimising the effects of shrinkage Material
Wetting (%)
Pinebark
18
Brown coal
59
L.S.D. 5%
L.S.D. 1%
6.2
8.9
that, after minimising the effects of shrinkage, brown coal shows hydrop h o b i c p r o p e r t i e s w h e n d r y , a b s o r b i n g 59% o f 20 m l a d d e d t o t h e t o p o f t h e m e d i u m . S i n c e t h e w e t t a b i l i t y o f b r o w n c o a l is i n v e r s e l y r e l a t e d t o its d r y n e s s ( F i g . 2), i t w o u l d a p p e a r , h o w e v e r , t h a t s h r i n k a g e is t h e d o m i n a n t f a c t o r in its p o o r r e - w e t t i n g p r o p e r t i e s .
54
100 >-
80
i
,z 40 o e~
20
i
2
3 SHRINKAGE
Fig. 3. T h e
4
5
(mm)
shrinkage (X) and wettability (Y) of clay loam (A), brown coal (*), Y = 9 6 . 0 - - 1 8 . 0 X + 2 . 2 X 2 , r -- 0.85**; pinebark (D), Y = 96.4 -- 37.2X + 12.7X2 , r = 0.74**. Y = 106.9
relationship
-- 21.9X
between
+ 1.6X
2 , r = 0.88**;
The wettability of the pinebark also declined as it dried out, b u t the relationship was n o t linear (Table V, Fig. 2). Since pinebark shrinks very little (Table II), its poor wettability when dry appears related to its hydrophobic properties which increase with drying, giving rise to the curvilinear relationship shown in Fig. 2. Table III shows that when the effects of shrink. age are minimised, dry pinebark is 3 times more h y d r o p h o b i c than brown coal. Water added to dry pinebark mostly runs over the surface and down the sides of the container with little penetration into the medium itself. The wettability of the clay loam soil decreased as it dried out, b u t in contrast to pinebark, the rate of reduction in wettability decreased as this medium dried o u t (Table V, Fig. 2). The curvilinear relationship between wetting and shrinkage of clay loam (Figs. 2 and 3) must be due to some offsetting of the shrinkage effects by increased hydrophilic properties of the material when it is dry, otherwise the relationship would be linear like that for brown coal. Pinebark, brown coal and clay loam all have poor wetting properties if they dry o u t in a p o t (FIT. 2). P i n e b a r k and b r o w n coal c o m b i n a t i o n s . -- The wetting properties of dry
pinebark and brown coal container mixtures, especially the mixture of 1 pinebark: 2 brown coal, were inferior to those of the individual materials (Fig. 4a and Table III). This could be the result of excessive shrinkage of brown coal combined with the h y d r o p h o b i c nature of dry pinebark, the interaction causing the water to run over the t o p of the dry mixture and down the space between the mixture and the side of the container. Such mixes are difficult t o wet when dry, holding only a third of the original
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INITIAL CONTAINER CAPACITY
Fig. 4. (a) The effect of water content on the wettability of brown coal (e), pinebark (c), 2 p i n e b a r k : l brown coal (A), pinebark:brown coal (T) and pin•bark:2 brown coal (=). (b) The effect of water content on the wettability of coarse sand (•), pinebark (=), pinebark:2 coarse sand (o), pin•bark:coarse sand (V) and 2 pin•bark:coarse sand (A). (c) The effect of water content on the wettability of pin•bark-based container mixtures; 2 pin•bark: 1 coarse sand (•), 2 p i n e b a r k : l brown coal (A), 2 p i n e b a r k : l brown coal:l coarse sand (•), 2 p i n e b a r k : l clay l o a m : l coarse sand (V), 4 p i n e b a r k : l brown coal:l coarse sand (o). Percentage by volume of coarse sand is indicated in parentheses.
TABLE IV Percentage of initial container capacity obtained from a single watering after 8 days of drying. Values with the. same subscript are not significantly different, which shows that mixtures of pinebark and brown coal have poorer wetting properties than the materials themselves Media
Re-wettability
Pinebark 2 P i n e b a r k : l brown coal 1 P i n e b a r k : l brown coal 1 Pinebark:2 brown coal Brown coal
83.5 65.1 68.3 55.9 76.2
L.S.D.
7.8 10.4
(%)
5% 1%
a b b c a
96 96 96 96 96 32 32 32 32 32 32 32 32 32 32 32 32
Coarse sand Sandy loam Clay l o a m B r o w n coal Pinebark Coarse sand B r o w n coal Pinebark 2 pinebark:l 1 pinebark:l 1 pinebark:2 2 pinebark:l 1 pinebark:l 1 pinebark:2 2 pinebark:l 2 pinebark:l 4 pinebark:l coarse sand coarse sand coarse sand b r o w n coal b r o w n coal b r o w n coal brown coal:l coarse sand clay l o a m : l coarse sand brown coal:l coarse sand
Days of drying
Medium
Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y
= = = = = = = = = = = = = = =
Y = 69.4
+ 0.56X
--
0.0046X 2 43.3 -- 0.033X + 0.0071X 2 48.0 + 0.64X 32.6 + 1 . 5 9 X - - 0 . 0 1 0 X 2 174.0 + 0.16X 60.7 + 0 . 6 4 X 34.4 + 2.05X-- 0.15X 2 81.1 + 0.86X- 0.0067X 2 79.2 + 0.97X -- 0.094X 2 96.1 + 0.54X 22.0 + 2.05X- 0.12X 2 44.7 + 0 . 9 0 X 28.0 + 0.90X 63.0 + 1.22X-- 0.065X 2 62.6 -- 0.28X + 0.09X 2 56.5 + 1 . 4 2 X - - 0.91X 2
Y = 115.8 + 0.29X
Equation
0.13 0.87 0.88 0.85 0.96 0.12 0.81 0.94 0.77 0.90 0.84 0.98 0.96 0.96 0.95 0.84 0.94
Regression coefficient
N.S. 1 1 1 1 N.S. 1 1 1 1 1 1 1 1 1 1 1
Significance (%)
R e l a t i o n s h i p s b e t w e e n m o i s t u r e c o n t e n t ( X ) a n d w e t t a b i l i t y (Y). M o i s t u r e c o n t e n t (X) a n d r e - w e t t a b i l i t y ( Y ) are e x p r e s s e d as p e r c e n t a g e o f initial c o n t a i n e r c a p a c i t y ( W h i t e a n d M a s t a l e r z , 1 9 6 6 )
TABLE V
CJ I
58 container capacity (Fig. 4a). Since we have previously shown pinebark/ brown coal mixtures to have good water relations if they are not allowed to dry out (Beardsell et al., 1979b), the re-wetting difficulties are simply avoided if the mixtures are prevented from drying out during nursery production. As in the first experiment (see Fig. 2), the wettability of brown coal was directly related to moisture content and pinebark had decreasing wettability with drying (Fig. 4a). The wettabilities of the 1:2 and 1:1 pinebark/ brown coal mixtures were also directly related to moisture content and were thus largely influenced by the brown coal, whereas the moisture content of 2 pinebark: 1 brown coal had a curvilinear relationship with wettability, largely influenced by the pinebark. Figure 4a and Table IV clearly show that 1:2 and 2:1 mixtures of pinebark and brown coal had very poor re-wetting properties as they dried out. and coarse sand combinations. - - Figures 2, 4b and 4c show that the superior wetting-properties of coarse sand are transferred to mixtures with pinebark in proportion to the amount of coarse sand used. To achieve acceptable levels of wettability when dry (> 80% of initial container capacity), media need to contain at least 30% by volume of coarse sand. In the media 2:1:1 pinebark:coarse sand:brown coal (25% sand) and 4:1:1 pinebark:coarse sand:brown coal (17% sand), re-wettability after complete drying out decreased to only 60% of the initial container capacity. Figure 4c shows that when clay loam was substituted for brown coal (comparing 2:1:1 pinebark:coarse sand:clay loam with 2:1:1 pinebark:coarse sand: brown coal), mixture properties were dominated b y the clay loam (see Fig. 2), and wettability decreased rapidly in the early stages because of shrinkage of the media but levelled off to approximately 60% initial container capacity. The direct effect of incorporating coarse sand into dried-out pinebark/brown coal mixtures is evidenced by the 20% re-wetting of 2 pinebark: 1 brown coal compared to 60% re-wetting of 2 pinebark: 1 brown coal:l coarse sand after both have completely dried out (Fig. 4c). This dramatically illustrates the benefit of incorporating a material which has good wetting-properties when dry into a container mixture. Although earlier work (Beardsell et al., 1979b) showed that coarse sand had a very low water-holding capacity, it is an important component in container mixtures which are liable to dry out, because it aids water penetration. Increasing the amount of sand in a mix from 17 to 30% by volume does, however, reduce the available water-holding capacity by approximately 17% (estimated from Beardsell et al., 1979b) and increases the weight of the mixture also by 17% {from the dry weights of the media used in this experiment). Thus, it is better nursery practice to prevent container media from drying out rather than to add coarse sand.
Pinebark
59 ACKNOWLEDGEMENTS We w o u l d like t o t h a n k Messrs. R. J a r d i n e a n d D. Richards for statistical analysis, a n d Miss D. F o n t a n a f o r technical assistance.
REFERENCES Airhart, D.L., Natarella, N.J. and Pokorny, F.A., 1978. Influence of initial moisture content on wettability of a milled pinebark medium. HortScience, 13: 432--434. Beardsell, D.V., Nichols, D.G. and Jones, D.L., 1979a. Physical properties of nursery potting mixtures. Scientia Hortic., 11: 1--8. Beardsell, D.V., Nichols, D.G. and Jones, D.L., 1979b. Water relations of nursery potting media. Scientia Hortic., 11: 9--17. Gehring, J.M. and Lewis, A.J., 1980. Effect of hydrogel on wilting and moisture stress of bedding plants. J. Am. Soc. Hortic. Sci., 105: 511--513. Solbraa, K., 1979. Composting of bark. I. Different bark qualities and their uses in plant production. Medd. Nor. Inst. Skogforsoeksves., 34: 281--333. White, J.W. and Mastalerz, J.W., 1966. Soil moisture as related to container capacity. J. Am. Soc. Hortic. Sci., 89: 758--765.