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Physical properties of media for container-grown crops. I. New Zealand peats and wood wastes
Scientia Horticulturae, 10 (1979) 317--323
317
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
PHYSICAL PROPERTIES OF MEDIA FOR CONTAINER-GROWN CROPS. I. NEW ZEALAND PEATS AND WOOD WASTES
M. PRASAD
Horticultural Research Centre, Research Division, Ministry of Agriculture and Fisheries, Levin (New Zealand) (Received 6 November 1978)
ABSTRACT Prasad, M., 1979. Physical properties of media for container-grown crops. I. New Zealand peats and wood wastes. Scientia Hortic., 10: 317--323. Physical properties of New Zealand peats from 5 sources and of wood wastes, bark and sawdust were evaluated in relation to container-grown crops. For comparative purposes, Irish peat was included. All the peats had adequate air space (AS), but the Springhill peat and New Zealand Forest Service bark and sawdust had a particularly high AS (35--38%). Easily available water (EAW) was also adequate in all peats. New Zealand Forest Service bark and sawdust had inadequate easily available water (EAW, 10--12%), but grinding the bark increased this property. All the peats had similar water-buffering capacity (WBC) with the Irish peat having the highest value. The wood waste materials had inadequate WBC. Total porosity was generally adequate in all materials studied and was highest in Springhill peat. The bulk density (BD) was closely related to degree of decomposition (r = 0.95"**) and also inversely related to AS and total porosity (r = -0.82* and r = -0.65, respectively).
INTRODUCTION
A wide range of composts is being used by nurserymen in New Zealand. The basic constituent is frequently New Zealand peat, although small quantities of imported Irish peat are being used. A recent development has been the export of small quantities of New Zealand peat. Information on the physical properties of New Zealand peats, presently being exploited for horticultural use, is fragmentary (Goh and Haynes, 1977). Hauraki peat is the peat most widely used in New Zealand, other peats being used in much smaller quantities. The objective of this investigation was to determine some of the physical properties of New Zealand peats and wood wastes and compare them with the imported Irish peat. MATERIALS AND METHODS
Peat from 5 sources, 2 from the North Island and 3 from the South Island, as well as Irish peat for comparison, were included. In addition, wood wastes,
318 namely Pinus radiata bark and sawdust, were studied. Details of the peats and wood wastes used are given in Table 1. Particle size determination. -- Particle size was determined on each batch of samples used for water retention determination. Oven-dried samples were sieved according to the m e t h o d of Boggie and Robertson (1972). The samples were put on the t o p m o s t sieve of a column of sieves placed on a mechanical shaker and shaken for 5 min at 180 shakes min -1. Degree of decomposition, p H and conductivity. -- The degree of decomposition was assessed on the processed peat according to the Von Post scale (Puustjarvi and Robertson, 1975). A measure of acidity was obtained by recording pH on an air-dried sample using a substrate to water ratio of 1:2 v/v. Conductivity was determined on a 1:1.5 water extract (Sonneveld et al., 1974). Porosity and water-holding capacity. -- In order to determine the water release characteristics of these materials, the samples were first moistened to a moisture content corresponding to pF 1.5--2.0 by eye estimation. The materials were then packed into two 80-ml cylinders (r = 2.5 cm, h = 4.1 cm). The upper cylinder {open at both ends) was m o u n t e d on the lower cylinder whose base was fitted with a fine mesh nylon cloth. The cylinders were then filled with the sample and compressed at 1 of 2 weights, 0.5 g cm -2 or 0.1 g cm -2 The upper cylinder was then removed and the substrate cut away until level with the upper end of the lower cylinder. The samples in the cylinders were then saturated with water in a trough for at least 16 h with the water level almost to the top end of the cylinder. They were then weighed and put on a tension table constructed according to Jamison and Reed (1949). Problems arose while weighing the saturated sample, as water drained freely from the container. In order to get uniformity, the saturated samples were weighed within 2--3 s of taking them off the trough. Suctions of 10, 31, 50 and 100 cm (pF 1.0, 1.5, 1.7 and 2.0) were applied, and the sample weighed at each tension after equilibration. Normally 24--48 h were required to establish equilibrium at each tension. When the samples had been weighed after equilibrium at 100 cm, they were oven-dried at 105°C for 24 h and re-weighed. The numbers of readings made on the tension table (Table 1, second column) had 3 or 4 replicate samples for each measurement. Total porosity (TP) was defined as the moisture content at zero suction. The volume of water between TP and moisture content at 10 cm suction represented air space (AS). The easily available water (EAW) was defined as the a m o u n t of water released from the material when the suction was increased from 10 to 50 cm. The water-buffering capacity (WBC) was defined as the quantity of water released from 50--100 cm suction. Water retention at pF 4.2 was determined using a high pressure plate apparatus. Moisture content between pF 2 and 4.2 has been designated as difficultly available water (DAW).
319 RESULTS AND DISCUSSION The optimum levels of AS, EAW, WBC and TP were defined by De Boodt and Verdonck {1972), were subsequently used by Bunt (1974), Maas and Adamson (1975), Van der Boon (1975) and Goh and Haynes (1977), and were taken as points of reference in this paper. Puustjarvi and Robertson (1975) believe that moisture held at suctions from 10 to 100 cm are relevant to intensive glasshouse production. With packing at low compression, {0.1 kg cm-2), equivalent to light potting, there was shrinkage of materials immediately after saturation. Volume corrections were not made for this shrinkage. Therefore the values obtained were underestimated and were omitted. In general, the results obtained from light packing gave similar trends to those obtained from heavier packing. The peats varied moderately in degree of decomposition (Table 1). Also, within a particular type of peat, there was a moderate variation in particle size. This conforms with commercial conditions. The AS was particularly high in the case of Springhill peat, and Hauraki peat also had a higher AS than Irish peat (Table 2). The Dipton and Wyndham peat had similar AS to Irish peat while the Cambridge peat had a lower AS. The AS for Dipton is similar to that reported by Goh and Haynes (1977), although their Dipton peat was more decomposed. The AS of the Irish peat is similar to the AS of the peats used by De Boodt et al. (1972) and Boggie (1970). Both N.Z.F.S. bark and sawdust had much higher AS than Irish peat, but the Fine Bark had similar AS. The AS of sawdust was similar to that reported by Goh and Haynes (1977). All the materials had adequate AS for container-grown crops, assuming that pots are at least 10 cm high (De Boodt and Verdonck, 1972; Havis and Hamilton, 1976; Paul and Lee, 1976; Puustjarvi, 1974; Stern et al., 1975). The Irish peat, together with Wyndham peat, had the highest amount of EAW (Table 2). The Springhill, Dipton, Cambridge and Hauraki peats had lower amounts of EAW, but the values were adequate. Goh and Haynes (1977) reported slightly higher EAW for their Dipton peat and this could be due to greater decomposition of their peat. Wyndham peat, which came from the Mataura region, behaved similarly to the less decomposed Mataura peat (Goh and Haynes, 1977) in so far as it had a well balanced and adequate AS and EAW. The 2 wood-waste materials, N.Z.F.S. bark and sawdust, had inadequate EAW. Goh and Haynes (1977) also reported low EAW in their sawdust. Grinding the bark increased the EAW to acceptable levels. De Boodt et al. (1972) reported that EAW of their bark was increased by composting. All the New Zealand peats had similar WBC to the Irish peat (Table 2). The WBC values were adequate for container-grown crops at heavier packing for all peats. The 2 wood-waste materials had inadequate WBC, but grinding the bark increased its WBC. The moisture content between pF 2 and pF 4.2 has been designated here as difficultly available water (DAW). It is generally recognised that water available at this tension range is of limited value in intensive horticulture
320
(Puustjarvi and Robertson, 1975). Nevertheless, it is interesting to note that DAW is low in N.Z.F.S. bark and this c o m p o u n d e d with inadequate EAW and WBC would make plants growing on it particularly susceptible to wilting (Table 2). The lower EAW and WBC of Springhill, Dipton and Cambridge peat in relation to Irish peat, is offset to a small extent by slightly higher amounts of DAW. The BD was closely related to the degree of decomposition of peat (r = 0.95, P = 0.001) and these results are similar to those reported by Puustjarvi and Robertson (1975). There was a close inverse relationship between BD and AS (r = -0.82, P = 0.05). Boelter (1969) also found a good relationship between water content at 10 cm suction and BD. Total porosity was highest in Springhill peat while the 2 barks had the lowest TP (Table 2). The values for all materials were adequate for containergrown crops (Conover, 1967; De Boodt and Verdonck, 1972; Havis and Hamilton, 1976). There was an inverse relationship between BD and TP (r = - 0 . 6 5 , P = 0.1). These results agreed with the findings of Boggie and Robertson (1972). Due to swelling of Springhill peat on saturation, the volume of the heavily packed sample exceeded the volume of the container by a b o u t 6--8 ml and volume corrections had to be made. In conclusion, the results showed that although New Zealand peats vary as regards physical properties, all of them appeared to be suitable as a growth medium. The best materials compared favourably in physical properties with the imported Irish peat. In addition, the results showed that the balance between AS and available water in bark could be improved by grinding. ACKNOWLEDGEMENTS
Thanks are expressed to Smiths Soil Industries, Auckland for supplying the Springhill, Dipton, Wyndham and some of the Hauraki peat, and to New Zealand Forest Service, Waipa for supplying the bark. The technical assistance of Mrs. D. Reid is gratefully acknowledged.
REFERENCES Boelter, D.H., 1969. Physical properties of peat as related to degree of decomposition. Soil Sci. Soc. Am., 33: 606--609. Boggie, R., 1970. Moisture characteristics of some peat--sand mixtures. Sci. Hortic., 22: 87--91. Boggie, R. and Robertson, R.A., 1972. Evaluation of horticultural peat in Britain. 4th Int. Peat Congr., III: 185--192. Bunt, A.C., 1974. Some physical and chemical characteristics of loamless pot-plant substrates and their relationship to plant growth. Acta Hortic., 37: 1954--1965. Conover, C.A., 1967. Soil mixes for ornamental plants. Fla. Flower Grow., 4 (4): 1--4. Davoren, A., 1978. A Survey of New Zealand Peat Resources. University of Waikato, N.Z., 157 pp. De Boodt, M. and Verdonck, O., 1972. The physical properties of the substrates in horticulture. Acta Hortic., 26: 37--44.
321 De Boodt, M., Cappaert, I. and Verdonck, O., 1972. The utilisation of basic waste in comparison with peat as a substrate for ornamental plants. 4th Int. Peat Congr., V: 193--205. Gob, K.M. and Haynes, R.J., 1977. Evaluation of potting media for commercial nursery production of container-grown plants. Physical and chemical characteristics of soil and soilless media and their constituents. N.Z.J. Agric. Res., 20: 363--370. Havis, J.R. and Hamilton, W.W., 1976. Physical properties of container media. J. Arboric., 2: 139--140. Jamison, V.C. and Reed, I.F., 1949. Durable asbestos tension tables. Soil Sci., 67: 311--318. Maas, E.F. and Adamson, R.M., 1975. Peat, bark and sawdust mixtures for nursery substrates. Acta Hortic., 50: 147--151. Paul, J.L. and Lee, C.I., 1976. Relation between growth of chrysanthemums and aeration of various container media. J. Am. Soc. Hortic. Sci., 101: 500--503. Puustjarvi, V., 1974. Physical properties of peat used in horticulture. Acta Hortic., 37: 1922--1929. Puustjarvi, V. and Robertson, R.A., 1975. Physical and chemical properties. In: D.W. Robinson and J.G.D. Lamb (Editors), Peat in Horticulture. Academic Press, London, New York, San Francisco, pp. 23--38. Sonneveld, C.J., Van den Ende, J. and van Dijk, P.A., 1974. Analysis of growing media by means of a 1 : 11/2 volume abstract. Commun. Soil Sci. Plant Anal., 5: 183--202. Stern, J.H., White, J.W., Cunningham, R.L. and Cole, R.H., 1975. Relationship among irrigation media regimes and plant growth. Plant Soil, 43: 433--441. Van der Boon, J., 1975. Peat as a forcing medium for tulips. Acta Hortic., 50: 69--82.
2
2
3
3
9
No. of readings
2 N.Z. Forest Service bark 4 Fine bark 3 Irish peat (medium grade) 6
Hauraki peat (N. Island) Springhill peat (S. Island) Dipton peat (S. Island) Wyndham peat (S. Island) Cambridge peat (N. Island) Sawdust
Material
0 30.8 (24.5--42.3)
39.7 (29.5--47.4) 65.7 (59.4--71.9) 43.1 (32.2--48.6) 48.2 (48.2--52.8) 33.0 (29.2--36.9) 29.5 (26.8--32.2) 19.8 (6.0--13.8)
8.6 (4.6--14.6) 5.4 (5.0--5.9) 11.0 (8.7--13.0) 11.8 (14.3--9.4) 16.3 (14.6--18.1) 20.2 (18.2--22.2) 10.2 (8.8--11.2) 5.7 (5.3--5.8) 14.6 (5.0--19.7)
32.5 (25.2--42.9) 21.0 (15.7--21.9) 30.7 (28.0--34.4) 19.7 (20.0--19.7) 32.2 (30.2--34.5) 48.5 (44.5--22.2) 42.9 (39.2--49.2) 32.4 (27.9--35.3) 31.7 (26.9--37.9)
% of particles in the size ranges (u) >3180 2460--3180 1000--2460 19.2 (4.2--20.8) 7.9 (4.1--12.8) 15.2 (6.1--24.5) 17.9 (17.4--18.4 18.5 (18.0--19.1 1.8 (1.0--2.5) 37.1 (30.6--44.8 61.6 (58.2--66.3) 22.9 (18.0--30.2)
<1000
4.4 3.8
H3
4.4
--
--
5.6
3.7
3.6
3.8
4.7
3.4
pH
--
H s
H4
H4--H s
H2--H4
H3--H 4
Degree of decomposition
0.20
0.07
0.06
0.06
0.47
0.55
0.19
0.22
0.11
Conductivity (mS)
Particle-size distribution and some properties of New Zealand peats and wood waste materials. Botanical composition of peats: Hauraki, mostly Sphagnum but also Calorophus, Gleichenia and Carex; South Island, varying amounts of Sphagnum, Calorophus, Gleicheria and Baumea; Cambridge, mostly Restiad but also Calorophus and Gleicheria; Irish, principally Sphagnum (Davoren, 1978). Figures in brackets give the range of values
TABLE1
t~ b~
Ideal s u b s t r a t e
Irish peat
bark Fine bark
N.Z. F o r e s t Service
Sawdust
Cambridge peat
Wyndham peat
Dipton peat
Springhill peat
Hauraki peat
Material
20--30
20--30
(8.3--12.5) 18.0 b (15.8--21.0) 30.4 d (27.3--33.4)
(8.4--13.5) 9.9 a
(36.6--42.0) 38.1 d
(33.4--41.9) 22.0 ab (21.0--23.4) 24.1 b (22.6--27.8)
(21.0--30.1) 25.1 c (22.6--27.3) 25.9 c (25.4--26.5) 28.4 cd (26.6--30.0) 24.9 c (23.8--26.0) 11.0 a
4--10
(0.8--1.0) 2.5 b (1.1--3.4) 4.9 d (3.0--5.3)
(0.9--2.1) 0.9 a
(2.8--6.0) 3.6 c (3.3--4.0) 4.1 c (3.9--4.6) 4.1 c (3.8--4.4) 3.8 c (3.5--4.1) 1.5 ab
4.0 c
(% volume)
(% volume) 24.6 c
Water-buffering capacity
Easily available water
(22.1--34.6) 35.3 d (32.7--37.8) 21.0 ab (20.5--21.4) 26.9 bc (24.8--28.9) 19.8 a (19.7--19.8) 39.3 d
30.3 c
Air space (% v o l u m e )
--
16.1
15.9
8.6
15.1
18.8
19.9
19.9
19.9
14.2
(% volume)
--
(0.208--0.233) 0.228 e (0.224--0.233) 0.114 b (0.104--0.123)
(0.124--0.154) 0 . 2 1 4 e)
(0.114--0.158) 0.069 a (0.066--0.076) 0.163 d (0.158--0.168) 0.144 cd (0.136--0.151) 0.231 e (0.223--0.229) 0.139 c
0.138 c
Difficultly available Bulk d e n s i t y water (g cc-' )
85
(78.0--80.8) 79.0 a (77.9--79.6) 89.4 b (85.6--94.5)
(80.3--85.6) 78.9 a
(79.3--95.3) 94.5 c (93.9--95.1) 88.6 b (87.3--90.3) 95.4 c (94.9--95.9) 86.0 b (83.5--88.5) 83.0 ab
87.1 b
(% volume)
Total porosity
Physical p r o p e r t i e s o f N e w Z e a l a n d p e a t s a n d w o o d wastes. Values in t h e s a m e c o l u m n f o l l o w e d b y s a m e l e t t e r s are n o t s i g n i f i c a n t l y d i f f e r e n t at 5% p r o b a b i l i t y level. Figures in b r a c k e t s give t h e range o f values. Only o n e m e a s u r e m e n t was m a d e at p F 4.2 (for D A W )
TABLE 2
bO
317
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
PHYSICAL PROPERTIES OF MEDIA FOR CONTAINER-GROWN CROPS. I. NEW ZEALAND PEATS AND WOOD WASTES
M. PRASAD
Horticultural Research Centre, Research Division, Ministry of Agriculture and Fisheries, Levin (New Zealand) (Received 6 November 1978)
ABSTRACT Prasad, M., 1979. Physical properties of media for container-grown crops. I. New Zealand peats and wood wastes. Scientia Hortic., 10: 317--323. Physical properties of New Zealand peats from 5 sources and of wood wastes, bark and sawdust were evaluated in relation to container-grown crops. For comparative purposes, Irish peat was included. All the peats had adequate air space (AS), but the Springhill peat and New Zealand Forest Service bark and sawdust had a particularly high AS (35--38%). Easily available water (EAW) was also adequate in all peats. New Zealand Forest Service bark and sawdust had inadequate easily available water (EAW, 10--12%), but grinding the bark increased this property. All the peats had similar water-buffering capacity (WBC) with the Irish peat having the highest value. The wood waste materials had inadequate WBC. Total porosity was generally adequate in all materials studied and was highest in Springhill peat. The bulk density (BD) was closely related to degree of decomposition (r = 0.95"**) and also inversely related to AS and total porosity (r = -0.82* and r = -0.65, respectively).
INTRODUCTION
A wide range of composts is being used by nurserymen in New Zealand. The basic constituent is frequently New Zealand peat, although small quantities of imported Irish peat are being used. A recent development has been the export of small quantities of New Zealand peat. Information on the physical properties of New Zealand peats, presently being exploited for horticultural use, is fragmentary (Goh and Haynes, 1977). Hauraki peat is the peat most widely used in New Zealand, other peats being used in much smaller quantities. The objective of this investigation was to determine some of the physical properties of New Zealand peats and wood wastes and compare them with the imported Irish peat. MATERIALS AND METHODS
Peat from 5 sources, 2 from the North Island and 3 from the South Island, as well as Irish peat for comparison, were included. In addition, wood wastes,
318 namely Pinus radiata bark and sawdust, were studied. Details of the peats and wood wastes used are given in Table 1. Particle size determination. -- Particle size was determined on each batch of samples used for water retention determination. Oven-dried samples were sieved according to the m e t h o d of Boggie and Robertson (1972). The samples were put on the t o p m o s t sieve of a column of sieves placed on a mechanical shaker and shaken for 5 min at 180 shakes min -1. Degree of decomposition, p H and conductivity. -- The degree of decomposition was assessed on the processed peat according to the Von Post scale (Puustjarvi and Robertson, 1975). A measure of acidity was obtained by recording pH on an air-dried sample using a substrate to water ratio of 1:2 v/v. Conductivity was determined on a 1:1.5 water extract (Sonneveld et al., 1974). Porosity and water-holding capacity. -- In order to determine the water release characteristics of these materials, the samples were first moistened to a moisture content corresponding to pF 1.5--2.0 by eye estimation. The materials were then packed into two 80-ml cylinders (r = 2.5 cm, h = 4.1 cm). The upper cylinder {open at both ends) was m o u n t e d on the lower cylinder whose base was fitted with a fine mesh nylon cloth. The cylinders were then filled with the sample and compressed at 1 of 2 weights, 0.5 g cm -2 or 0.1 g cm -2 The upper cylinder was then removed and the substrate cut away until level with the upper end of the lower cylinder. The samples in the cylinders were then saturated with water in a trough for at least 16 h with the water level almost to the top end of the cylinder. They were then weighed and put on a tension table constructed according to Jamison and Reed (1949). Problems arose while weighing the saturated sample, as water drained freely from the container. In order to get uniformity, the saturated samples were weighed within 2--3 s of taking them off the trough. Suctions of 10, 31, 50 and 100 cm (pF 1.0, 1.5, 1.7 and 2.0) were applied, and the sample weighed at each tension after equilibration. Normally 24--48 h were required to establish equilibrium at each tension. When the samples had been weighed after equilibrium at 100 cm, they were oven-dried at 105°C for 24 h and re-weighed. The numbers of readings made on the tension table (Table 1, second column) had 3 or 4 replicate samples for each measurement. Total porosity (TP) was defined as the moisture content at zero suction. The volume of water between TP and moisture content at 10 cm suction represented air space (AS). The easily available water (EAW) was defined as the a m o u n t of water released from the material when the suction was increased from 10 to 50 cm. The water-buffering capacity (WBC) was defined as the quantity of water released from 50--100 cm suction. Water retention at pF 4.2 was determined using a high pressure plate apparatus. Moisture content between pF 2 and 4.2 has been designated as difficultly available water (DAW).
319 RESULTS AND DISCUSSION The optimum levels of AS, EAW, WBC and TP were defined by De Boodt and Verdonck {1972), were subsequently used by Bunt (1974), Maas and Adamson (1975), Van der Boon (1975) and Goh and Haynes (1977), and were taken as points of reference in this paper. Puustjarvi and Robertson (1975) believe that moisture held at suctions from 10 to 100 cm are relevant to intensive glasshouse production. With packing at low compression, {0.1 kg cm-2), equivalent to light potting, there was shrinkage of materials immediately after saturation. Volume corrections were not made for this shrinkage. Therefore the values obtained were underestimated and were omitted. In general, the results obtained from light packing gave similar trends to those obtained from heavier packing. The peats varied moderately in degree of decomposition (Table 1). Also, within a particular type of peat, there was a moderate variation in particle size. This conforms with commercial conditions. The AS was particularly high in the case of Springhill peat, and Hauraki peat also had a higher AS than Irish peat (Table 2). The Dipton and Wyndham peat had similar AS to Irish peat while the Cambridge peat had a lower AS. The AS for Dipton is similar to that reported by Goh and Haynes (1977), although their Dipton peat was more decomposed. The AS of the Irish peat is similar to the AS of the peats used by De Boodt et al. (1972) and Boggie (1970). Both N.Z.F.S. bark and sawdust had much higher AS than Irish peat, but the Fine Bark had similar AS. The AS of sawdust was similar to that reported by Goh and Haynes (1977). All the materials had adequate AS for container-grown crops, assuming that pots are at least 10 cm high (De Boodt and Verdonck, 1972; Havis and Hamilton, 1976; Paul and Lee, 1976; Puustjarvi, 1974; Stern et al., 1975). The Irish peat, together with Wyndham peat, had the highest amount of EAW (Table 2). The Springhill, Dipton, Cambridge and Hauraki peats had lower amounts of EAW, but the values were adequate. Goh and Haynes (1977) reported slightly higher EAW for their Dipton peat and this could be due to greater decomposition of their peat. Wyndham peat, which came from the Mataura region, behaved similarly to the less decomposed Mataura peat (Goh and Haynes, 1977) in so far as it had a well balanced and adequate AS and EAW. The 2 wood-waste materials, N.Z.F.S. bark and sawdust, had inadequate EAW. Goh and Haynes (1977) also reported low EAW in their sawdust. Grinding the bark increased the EAW to acceptable levels. De Boodt et al. (1972) reported that EAW of their bark was increased by composting. All the New Zealand peats had similar WBC to the Irish peat (Table 2). The WBC values were adequate for container-grown crops at heavier packing for all peats. The 2 wood-waste materials had inadequate WBC, but grinding the bark increased its WBC. The moisture content between pF 2 and pF 4.2 has been designated here as difficultly available water (DAW). It is generally recognised that water available at this tension range is of limited value in intensive horticulture
320
(Puustjarvi and Robertson, 1975). Nevertheless, it is interesting to note that DAW is low in N.Z.F.S. bark and this c o m p o u n d e d with inadequate EAW and WBC would make plants growing on it particularly susceptible to wilting (Table 2). The lower EAW and WBC of Springhill, Dipton and Cambridge peat in relation to Irish peat, is offset to a small extent by slightly higher amounts of DAW. The BD was closely related to the degree of decomposition of peat (r = 0.95, P = 0.001) and these results are similar to those reported by Puustjarvi and Robertson (1975). There was a close inverse relationship between BD and AS (r = -0.82, P = 0.05). Boelter (1969) also found a good relationship between water content at 10 cm suction and BD. Total porosity was highest in Springhill peat while the 2 barks had the lowest TP (Table 2). The values for all materials were adequate for containergrown crops (Conover, 1967; De Boodt and Verdonck, 1972; Havis and Hamilton, 1976). There was an inverse relationship between BD and TP (r = - 0 . 6 5 , P = 0.1). These results agreed with the findings of Boggie and Robertson (1972). Due to swelling of Springhill peat on saturation, the volume of the heavily packed sample exceeded the volume of the container by a b o u t 6--8 ml and volume corrections had to be made. In conclusion, the results showed that although New Zealand peats vary as regards physical properties, all of them appeared to be suitable as a growth medium. The best materials compared favourably in physical properties with the imported Irish peat. In addition, the results showed that the balance between AS and available water in bark could be improved by grinding. ACKNOWLEDGEMENTS
Thanks are expressed to Smiths Soil Industries, Auckland for supplying the Springhill, Dipton, Wyndham and some of the Hauraki peat, and to New Zealand Forest Service, Waipa for supplying the bark. The technical assistance of Mrs. D. Reid is gratefully acknowledged.
REFERENCES Boelter, D.H., 1969. Physical properties of peat as related to degree of decomposition. Soil Sci. Soc. Am., 33: 606--609. Boggie, R., 1970. Moisture characteristics of some peat--sand mixtures. Sci. Hortic., 22: 87--91. Boggie, R. and Robertson, R.A., 1972. Evaluation of horticultural peat in Britain. 4th Int. Peat Congr., III: 185--192. Bunt, A.C., 1974. Some physical and chemical characteristics of loamless pot-plant substrates and their relationship to plant growth. Acta Hortic., 37: 1954--1965. Conover, C.A., 1967. Soil mixes for ornamental plants. Fla. Flower Grow., 4 (4): 1--4. Davoren, A., 1978. A Survey of New Zealand Peat Resources. University of Waikato, N.Z., 157 pp. De Boodt, M. and Verdonck, O., 1972. The physical properties of the substrates in horticulture. Acta Hortic., 26: 37--44.
321 De Boodt, M., Cappaert, I. and Verdonck, O., 1972. The utilisation of basic waste in comparison with peat as a substrate for ornamental plants. 4th Int. Peat Congr., V: 193--205. Gob, K.M. and Haynes, R.J., 1977. Evaluation of potting media for commercial nursery production of container-grown plants. Physical and chemical characteristics of soil and soilless media and their constituents. N.Z.J. Agric. Res., 20: 363--370. Havis, J.R. and Hamilton, W.W., 1976. Physical properties of container media. J. Arboric., 2: 139--140. Jamison, V.C. and Reed, I.F., 1949. Durable asbestos tension tables. Soil Sci., 67: 311--318. Maas, E.F. and Adamson, R.M., 1975. Peat, bark and sawdust mixtures for nursery substrates. Acta Hortic., 50: 147--151. Paul, J.L. and Lee, C.I., 1976. Relation between growth of chrysanthemums and aeration of various container media. J. Am. Soc. Hortic. Sci., 101: 500--503. Puustjarvi, V., 1974. Physical properties of peat used in horticulture. Acta Hortic., 37: 1922--1929. Puustjarvi, V. and Robertson, R.A., 1975. Physical and chemical properties. In: D.W. Robinson and J.G.D. Lamb (Editors), Peat in Horticulture. Academic Press, London, New York, San Francisco, pp. 23--38. Sonneveld, C.J., Van den Ende, J. and van Dijk, P.A., 1974. Analysis of growing media by means of a 1 : 11/2 volume abstract. Commun. Soil Sci. Plant Anal., 5: 183--202. Stern, J.H., White, J.W., Cunningham, R.L. and Cole, R.H., 1975. Relationship among irrigation media regimes and plant growth. Plant Soil, 43: 433--441. Van der Boon, J., 1975. Peat as a forcing medium for tulips. Acta Hortic., 50: 69--82.
2
2
3
3
9
No. of readings
2 N.Z. Forest Service bark 4 Fine bark 3 Irish peat (medium grade) 6
Hauraki peat (N. Island) Springhill peat (S. Island) Dipton peat (S. Island) Wyndham peat (S. Island) Cambridge peat (N. Island) Sawdust
Material
0 30.8 (24.5--42.3)
39.7 (29.5--47.4) 65.7 (59.4--71.9) 43.1 (32.2--48.6) 48.2 (48.2--52.8) 33.0 (29.2--36.9) 29.5 (26.8--32.2) 19.8 (6.0--13.8)
8.6 (4.6--14.6) 5.4 (5.0--5.9) 11.0 (8.7--13.0) 11.8 (14.3--9.4) 16.3 (14.6--18.1) 20.2 (18.2--22.2) 10.2 (8.8--11.2) 5.7 (5.3--5.8) 14.6 (5.0--19.7)
32.5 (25.2--42.9) 21.0 (15.7--21.9) 30.7 (28.0--34.4) 19.7 (20.0--19.7) 32.2 (30.2--34.5) 48.5 (44.5--22.2) 42.9 (39.2--49.2) 32.4 (27.9--35.3) 31.7 (26.9--37.9)
% of particles in the size ranges (u) >3180 2460--3180 1000--2460 19.2 (4.2--20.8) 7.9 (4.1--12.8) 15.2 (6.1--24.5) 17.9 (17.4--18.4 18.5 (18.0--19.1 1.8 (1.0--2.5) 37.1 (30.6--44.8 61.6 (58.2--66.3) 22.9 (18.0--30.2)
<1000
4.4 3.8
H3
4.4
--
--
5.6
3.7
3.6
3.8
4.7
3.4
pH
--
H s
H4
H4--H s
H2--H4
H3--H 4
Degree of decomposition
0.20
0.07
0.06
0.06
0.47
0.55
0.19
0.22
0.11
Conductivity (mS)
Particle-size distribution and some properties of New Zealand peats and wood waste materials. Botanical composition of peats: Hauraki, mostly Sphagnum but also Calorophus, Gleichenia and Carex; South Island, varying amounts of Sphagnum, Calorophus, Gleicheria and Baumea; Cambridge, mostly Restiad but also Calorophus and Gleicheria; Irish, principally Sphagnum (Davoren, 1978). Figures in brackets give the range of values
TABLE1
t~ b~
Ideal s u b s t r a t e
Irish peat
bark Fine bark
N.Z. F o r e s t Service
Sawdust
Cambridge peat
Wyndham peat
Dipton peat
Springhill peat
Hauraki peat
Material
20--30
20--30
(8.3--12.5) 18.0 b (15.8--21.0) 30.4 d (27.3--33.4)
(8.4--13.5) 9.9 a
(36.6--42.0) 38.1 d
(33.4--41.9) 22.0 ab (21.0--23.4) 24.1 b (22.6--27.8)
(21.0--30.1) 25.1 c (22.6--27.3) 25.9 c (25.4--26.5) 28.4 cd (26.6--30.0) 24.9 c (23.8--26.0) 11.0 a
4--10
(0.8--1.0) 2.5 b (1.1--3.4) 4.9 d (3.0--5.3)
(0.9--2.1) 0.9 a
(2.8--6.0) 3.6 c (3.3--4.0) 4.1 c (3.9--4.6) 4.1 c (3.8--4.4) 3.8 c (3.5--4.1) 1.5 ab
4.0 c
(% volume)
(% volume) 24.6 c
Water-buffering capacity
Easily available water
(22.1--34.6) 35.3 d (32.7--37.8) 21.0 ab (20.5--21.4) 26.9 bc (24.8--28.9) 19.8 a (19.7--19.8) 39.3 d
30.3 c
Air space (% v o l u m e )
--
16.1
15.9
8.6
15.1
18.8
19.9
19.9
19.9
14.2
(% volume)
--
(0.208--0.233) 0.228 e (0.224--0.233) 0.114 b (0.104--0.123)
(0.124--0.154) 0 . 2 1 4 e)
(0.114--0.158) 0.069 a (0.066--0.076) 0.163 d (0.158--0.168) 0.144 cd (0.136--0.151) 0.231 e (0.223--0.229) 0.139 c
0.138 c
Difficultly available Bulk d e n s i t y water (g cc-' )
85
(78.0--80.8) 79.0 a (77.9--79.6) 89.4 b (85.6--94.5)
(80.3--85.6) 78.9 a
(79.3--95.3) 94.5 c (93.9--95.1) 88.6 b (87.3--90.3) 95.4 c (94.9--95.9) 86.0 b (83.5--88.5) 83.0 ab
87.1 b
(% volume)
Total porosity
Physical p r o p e r t i e s o f N e w Z e a l a n d p e a t s a n d w o o d wastes. Values in t h e s a m e c o l u m n f o l l o w e d b y s a m e l e t t e r s are n o t s i g n i f i c a n t l y d i f f e r e n t at 5% p r o b a b i l i t y level. Figures in b r a c k e t s give t h e range o f values. Only o n e m e a s u r e m e n t was m a d e at p F 4.2 (for D A W )
TABLE 2
bO