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Biomass production and nutrient cycling in Eucalyptus short rotation energy forests in New Zealand.
Bioresource Technology 85 (2002) 273–283
Biomass production and nutrient cycling in Eucalyptus short rotation energy forests in New Zealand. I: biomass and nutrient accumulation L.B. Guo a
a,*
, R.E.H. Sims a, D.J. Horne
b
Institute of Technology and Engineering, Massey University, Private Bag 11 222, Palmerston North, New Zealand b Institute of Natural Resources, Massey University, Private Bag 11 222, Palmerston North, New Zealand Received 28 March 2001; received in revised form 22 April 2002; accepted 4 May 2002
Abstract Accumulation of biomass and nutrients (N, P, K, Ca, Mg and Mn) was measured during the first 3-year rotation of three Eucalyptus short rotation forest species (E. botryoides, E. globulus and E. ovata) irrigated with meatworks effluent compared with no irrigation. E. globulus had the highest biomass and nutrient accumulation either irrigated with effluent or without irrigation. After 3year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn, but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca and Mg. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biomass; Nutrients; Accumulation; Eucalyptus; Short rotation forest; Effluent land treatment
1. Introduction Short rotation forests are a renewable source of energy and can reduce the energy demands currently met by fossil fuels. However, much of the concern about the sustainability of short rotation forest systems focuses on the question of depletion of soil nutrients. This is heightened by the harvesting of whole-trees together with the short harvest cycles (Heilman, 1992; Ericsson, 1994). For sustainable land use, the nutrient loss must be remedied by application of fertilisers, which usually increases the input costs and hence the energy cost from the biomass. Effluent from meatworks contains nutrients which could replace commercial fertilizer to provide nutrients as well as water for crop production (Marecos do Monte et al., 1989). Land treatment by applying the effluent to the soil would avoid disposal to the environment using waterways. In this case, frequent harvesting of the trees * Corresponding author. Present address: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia. Tel.: +61-2-62465267; fax: +61-2-6246-5000. E-mail address: [email protected] (L.B. Guo).
to remove large quantities of nutrients from the soil is essential for sustainable land use. In short rotation forest production systems, either linked with effluent land treatment or without, harvestable biomass and nutrients accumulated in the biomass are closely related to the end products and the nutrient removal from the systems. During tree growth, part of the above-ground biomass produced and nutrient uptake is returned to the soil surface via litter fall. The accumulation of biomass and nutrients is usually defined as above-ground biomass and nutrients in the standing trees, which are the parts of trees normally to be removed from the site. The overall aim of this study was to determine the flow of nutrients within eucalypt short rotation forest ecosystems, and provide information for the effective management of the systems, especially when linked with effluent land treatment. The specific objectives of the current part of this paper were to determine: (i) the biomass accumulation and the potential nutrient removal following whole tree harvesting of three selected eucalypt species during the first 3-year rotation of short rotation forests irrigated with meatworks effluent and without irrigation; and (ii) the distribution of biomass
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and nutrients in the standing trees at the end of the rotation.
2. Methods 2.1. Site, species and experimental design The study site was at the Richmond Meat Processors & Packers Ltd.’s processing plant at Oringi, which is adjacent to the Manawatu River, located near Dannevirke, New Zealand. Longitude is 176°010 E and latitude is 40°160 S. Monthly distributions of rainfall and temperature for 10-year averages (1986–1996) are shown in Fig. 1. The soils are Dannevirke-Kopua soils from alluvial deposits, and having textures of sandy loam overlying stony gravels with mostly medium to low natural fertility (National Resources Survey, 1971). Before the trees were planted, the site was occupied by pasture, which had been irrigated with meatworks effluent for 12 years. Three-month-old seedlings grown in root trainers were planted for 30 hectares in December 1993 at a density of 4167 stems/ha (1 m 2:4 m spacing). A split block experimental design was used with three blocks in the plantation. In each block, there were three subblocks of species, Eucalyptus botryoides (B), E. globulus (G), and E. ovata (O). Each sub-block was split into two plots for the treatments: without irrigation (N) and irrigated with effluent (I). Each of the 18 plots was 10 m 10 m, giving 40 trees per plot, and with a 10 m buffer zone between them. Next to each plot, a same size plot was established for mean tree sampling when the trees were 1 and 2 years old. Effluent from the meatworks (mixture of wastewater from stockyards, slaughter floor, casing and offal, pelt wash, etc.), stored in an anaerobic pond, was irrigated onto the plots at a rate of 20 mm/week using flood channels between the rows of trees planted on 100 mm high ridges. The chemical and biochemical characteris-
Table 1 Chemical composition of the effluent from the anaerobic pond of the Richmond meatworks at Oringi, Dannevirke, New Zealand Biochemical oxygen demand (g/m3 ) Chemical oxygen demand (g/m3 ) Total Kjeldahl nitrogen (g/m3 ) Ammoniac nitrogen (g/m3 ) Nitrate nitrogen (g/m3 ) Phosphorus (g/m3 ) Potassium (g/m3 ) Calcium (g/m3 ) Magnesium (g/m3 ) Manganese (g/m3 ) pH
400 1060 200 150 <0.2 20 90 25 7 0.4 6.8
tics of the effluent are shown in Table 1. The planned rotation length between coppice harvests was 3 years, but this study was conducted during the first rotation from 1994 to 1996. 2.2. Measurements and sampling Tree diameters, heights, and sampling of tree biomass were measured in December 1994, December 1995, and December 1996 when the trees were 1, 2 and 3 years old. Tree diameters were measured at ground level as they were 1 year old, but at breast height (1.4 m) thereafter. The mean tree method was used for destructive sampling as the mean basal area seems to be the best method for biomass estimation in even-aged stands of a single species (Parde, 1980). The mean trees were accessed according to tree mean height, and their mean diameter calculated from the mean basal area in each plot with account also being taken of the crown width. Three mean trees determined was selected and harvested in the same treatment plot next to each plot when the trees were 1 and 2 years old, while the mean trees for the final sampling were selected and harvested within each plot when the trees were 3 years old. The whole mean trees above-ground were harvested and stored in a cool room before processing. 2.3. Laboratory analyses
Fig. 1. Monthly rainfall and mean temperature for Dannevirke, New Zealand (10-year average from 1986 to 1996).
The mean trees were divided into five components: foliage, twig (<6.4 mm diameter), branch (6.5–25.4 mm diameter), bark and wood from stem and branches larger than 25.4 mm (Young and Carpenter, 1976). New soft shoots with young leaves not fully open and dead portions (including dead bark, twigs, branches, and leaves) were separated to give a total of seven categories. The size of the photosynthetic system was the leaf area index (LAI) being the area of leaves carried above a unit area of ground (Newbould, 1967). LAI was estimated from leaf biomass using a weight/leaf area conversion factor determined from a sub-sample of the leaves, their
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area was measured using a leaf area meter (LI-Cor LI3100). Samples of all tree parts were weighed after being oven dried at 80 °C to constant weight and then were ground to pass through a 1 mm sieve for nutrient analyses. Total N and total P were analysed using a Technicon Auto Analyser (Pulse Instrumentation Ltd., Saskatoon, Canada) following Kjeldahl digestion. K, Ca, Mg and Mn were analyzed using an atomic absorption spectroscopy (GBC 904 AA) following nitric acid digestion. Total oven dry (OD) biomass was obtained from the mean basal area of the trees in the plots and the sample trees as follows: P WT WP ¼ AP P AT
acted on the effects, but with some exceptions (Table 2). In the first year, effluent irrigation increased tree stem diameter at ground level (DG) in E. globulus but had no effects on the other two species (Fig. 2a). By year 2 and year 3, it increased the diameter at breast height (DBH) in all three species, except E. globulus at the end of the 3-year period. E. globulus irrigated with effluent produced the greatest DG in the first year, and E. botryoides the smallest. The DBH was larger in E. globulus and E. botryoides irrigated with effluent in the second year. At the end of the rotation, E. ovata irrigated with effluent caught up to E. globulus. The smallest DBH was found in both E. botryoides and E. ovata without irrigation.
where WP is the plot biomass (OD t/ha), AP is the plot basal area (m2 /ha), WT is the sample tree biomass (OD t/ tree), and AT is the sample tree basal area (m2 ). Nutrients accumulated in each tree component were estimated as follow:
Table 2 Tree performance and biomass accumulation of three eucalypt species (B ¼ E: botryoides; G ¼ E: globules; O ¼ E: ovata) in short rotation forests without irrigation (C) and irrigated with effluent (E)
NC ¼ 1000CN WC where NC is the nutrient accumulation (kg/ha) for each tree component in each plot, CN is the nutrient concentration (%) of the tree component, WC is the total biomass of the tree component (OD t/ha). Total nutrient accumulation in the standing trees was estimated from the nutrient accumulation in each of the tree components: n X NP ¼ Ni
Age Diameter (cm) (at ground level when 1 year old, and at breast height when P2 year old)
1
2
3
Species n ¼ 240
B G O LSD0:05
3.2 4.5 4.3 0.3
5.0 6.1 4.9 0.4
6.7 7.9 6.9 0.8
Treatment n ¼ 360
C E LSD0:05
3.8 4.1 0.1
5.0 5.6 0.5
6.8 7.5 0.7
Interaction Height (m)
Species n ¼ 240
B G O LSD0:05
1.3 1.9 2.0 0.2
2.4 4.9 4.3 0.5
4.5 7.0 5.8 0.6
Treatment n ¼ 360
C E LSD0:05
1.6 1.9 0.2
3.7 4.0 0.2
5.6 5.8 ns
1
where NP is plot nutrient accumulation (kg/ha), Ni is the nutrient accumulation in each tree component in each plot (kg/ha), n ¼ 7 (the number of tree components). 2.4. Statistical analysis All data from the split block design experiment were analysed using the SAS GLM procedure (SAS Institute, 1990). The model of a 2-factorial combination with 3 repeat measurements (year) was used for analysing the data of tree performance (diameter, height and LAI), biomass accumulation, and nutrient accumulation. Means were separated by the least significant difference (LSD) test when species, treatments and their interactions were significant (P < 0:05).
3. Results 3.1. Tree performance and biomass accumulation Species and treatment significantly affected tree performance and biomass accumulation, and they inter-
Interaction LAI (m2 /m2 )
Species n¼6
B G O LSD0:05
0.3 1.4 1.6 0.2
0.9 6.8 5.4 0.5
4.6 5.4 2.8 0.6
Treatment n¼9
C E LSD0:05
1.2 1.0 0.1
4.1 2.9 0.8
4.6 3.9 0.5
Interaction Biomass (OD t/ha)
Species n¼6
B G O LSD0:05
1.9 6.0 5.3 1.1
7.7 32.2 20.9 4.9
39.7 64.7 45.5 5.8
Treatment n¼9
C E LSD0:05
4.3 4.4 ns
17.5 22.9 4.3
42.4 57.5 6.9
Interaction ns denotes not significant. * P < 0:01. ** P < 0:05. *** P < 0:001.
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Fig. 2. Tree performance and biomass accumulation in eucalypt plantations: (a) diameter (at ground level when 1 year old and at breast height when P 2 years old), (b) height, (c) LAI and (d) biomass accumulation (N ¼ without irrigation; I ¼ irrigated with effluent; B ¼ E: botryoides; G ¼ E: globulus; O ¼ E: ovata; n ¼ 120, but 3 for LAI and biomass; vertical bars indicate LSD0:05 ).
E. globulus was the tallest species, and E. botryoides was the shortest during the 3-year period (Fig. 2b). Effluent irrigation increased tree height throughout the 3year period for E. botryoides, but by year 1 and year 3 for E. ovata, and by year 1 and year 2 for E. globulus. E. globulus trees without irrigation were taller than its trees irrigated with effluent at the end of the 3-year period. Effluent irrigation reduced LAI during the 3-year period except for E. botryoides at year 2, and for E. globulus at years 1 and 3 (Fig. 2c). There were significant differences in the LAI between the three species, except for E. globulus and E. ovata irrigated with effluent at year 1, and E. botryoides without irrigation and E. globulus at year 3. Relatively little biomass was accumulated in the first year (Table 2, Fig. 2d). There were significant differences in the above-ground biomass accumulation between the three species. E. globulus showed the best growth performance in the three studied species, either without irrigation or irrigated with effluent. At the end of the 3year period, 72 OD t/ha of above-ground biomass were accumulated in its stands irrigated with effluent. Effluent irrigation significantly increased the biomass accumulation in all three species after 2 and 3 years. At the end of the 3-year period, effluent application increased the total above-ground biomass accumulation by 19%, 24%
and 76% for E. botryoides, E. globulus and E. ovata, respectively. The response of E. ovata to effluent was significantly greater than that of the other two species. The distribution of biomass in the various tree components was also affected by effluent irrigation (Fig. 3a). Proportionally, less foliage biomass was found in the trees irrigated with effluent than in the trees without irrigation, but there were more twigs and branches. More wood was found in the trees irrigated with effluent than in the trees without irrigation, except for E. globulus, for their diameters were smaller and tree heights were lower than for trees without irrigation (Fig. 2). Overall, approximately half of the biomass was wood except in E. botryoides without irrigation (28%). 3.2. Nutrient accumulation Species and treatment significantly affected nutrient accumulation and they interacted on the effects even though there were some exceptions (Table 3). 3.3. Nitrogen There were significant differences in N accumulation between the three species, the trend being similar to the biomass accumulation (Table 3, Fig. 4a). Less N was
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277
Fig. 3. Biomass and nutrient distribution in the harvestable above-ground biomass components at the end of the 3-year period: (a) biomass, (b) N, (c) P, (d) K, (e) Ca, (f) Mg, and (g) Mn (the area of each chart depicts the comparative total biomass or nutrient accumulation).
accumulated in E. botryoides during the first 2 years, but by year 3 this species had accumulated around 400 kg/ha and caught up with E. globulus without irrigation and E. ovata irrigated with effluent. By the end of the 3-year period, E. globulus irrigated with effluent had accumu-
lated the greatest amount of N, and E. ovata without irrigation the least. The N distribution in the tree components was affected by the effluent irrigation (Fig. 3b). Proportionally, less N was found in the foliage of trees irrigated with
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Table 3 Nutrient accumulation (kg/ha) of three eucalypt species (B ¼ E: botryoides; G ¼ E: globules; O ¼ E: ovata) in short rotation forests without irrigation (C) and irrigated with effluent (E) Age N
21.0 80.9 69.5 15.9
87.6 285.8 166.4 53.1
406.9 541.3 322.8 58.6
Treatment n¼9
C E LSD0:05
50.3 63.9 9.6
154.0 205.8 42.3
355.2 492.2 76.4
Species n¼6
B G O LSD0:05
3.0 6.7 5.2 1.2
7.2 26.0 15.4 5.5
39.6 44.8 25.8 12.5
Treatment n¼9
C E LSD0:05
4.7 5.1 ns
12.5 19.9 2.3
28.7 44.6 19.2
Species n¼6
B G O LSD0:05
14.3 49.0 50.9 12.1
61.3 222.3 152.4 26.2
229.6 327.8 267.1 54.3
Treatment n¼9
C E LSD0:05
34.0 42.1 6.1
130.4 160.2 29.2
213.9 335.7 74.6
Interaction Ca
Species n¼6
B G O LSD0:05
21.4 97.1 36.5 9.7
43.7 117.8 173.0 53.1
235.3 291.9 233.4 58.6
Treatment n¼9
C E LSD0:05
65.9 37.4 10.5
136.4 86.6 42.3
302.1 204.9 76.4
Interaction Mg
Species n¼6
B G O LSD0:05
2.4 8.2 5.3 1.8
7.1 21.5 14.7 5.5
32.7 40.3 28.4 12.5
Treatment n¼9
C E LSD0:05
5.5 5.1 0.3
16.0 12.9 2.3
36.6 31.0 ns
B G O LSD0:05
1.1 4.9 3.6 0.9
7.8 23.1 15.2 6.2
29.9 47.7 27.9 14.3
C E LSD0:05
2.5 3.8 1.1 ns
9.9 20.8 9.2 ns
21.8 48.5 14.3
Interaction Mn
3
B G O LSD0:05
Interaction K
2
Species n¼6
Interaction P
1
Species n¼6
Treatment n¼9 Interaction ns denotes not significant. * P < 0:05. ** P < 0:01. *** P < 0:001.
effluent than those without irrigation, and more was found in the twigs, branches and wood. Overall, less than one quarter of the total N was accumulated in the wood for all three species. 3.4. Phosphorus There were significant differences in P accumulation between the three species (Table 3, Fig. 4b). Less P was accumulated in E. botryoides in the first 2 years. In the third year, the accumulation of P in this species reached approximately 40 kg/ha and caught up with E. globulus without irrigation and E. ovata irrigated with effluent. At the end of the rotation, E. globulus trees irrigated with effluent accumulated the greatest amount of P, and E. ovata without irrigation accumulated the least, where little net P accumulation occurred during the third year. The P distribution in the various tree components was also affected by the effluent irrigation (Fig. 3c). Proportionally, less P was found in foliage of the trees irrigated with effluent than in that of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides. More P was found in the wood of trees irrigated with effluent than in the wood of trees without irrigation except in E. globulus. 3.5. Potassium There were significant differences in K accumulation between the three species (Table 3, Fig. 4c). Effluent irrigation only enhanced K accumulation in E. globulus at first, then in E. botryoides in the second year. By year 3, effluent irrigation significantly enhanced K accumulation in all three species. During the third year, no net K accumulation occurred in E. ovata without irrigation, but a significant amount was accumulated in E. ovata irrigated with effluent which caught up with E. globulus irrigated with effluent. Proportionally, less K was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides (Fig. 3d). More K was found in the wood of the trees irrigated with effluent than in the trees without irrigation, but not for E. globulus. 3.6. Calcium Effluent irrigation retarded Ca accumulation in all three species although it increased the biomass accumulation (Fig. 4d). Ca was accumulated in E. ovata without irrigation most sharply in the second year and in E. botryoides without irrigation in the third year. The final accumulation over the 3-year period was greatest for E. globulus and E. botryoides without irrigation.
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Fig. 4. Nutrient accumulation in eucalypt plantations over the 3-year period: (a) N, (b) P, (c) K, (d) Ca, (e) Mg, and (f) Mn (N ¼ without irrigation; I ¼ irrigated with effluent; B ¼ E: botryoides; G ¼ E: globulus; O ¼ E: ovata; vertical bars indicate LSD0:05 ; n ¼ 3).
Proportionally, less Ca was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the barks (Fig. 3e). Approximately double Ca was stored in the wood of the trees irrigated with effluent than in the trees without irrigation, except for E. globulus. In E. ovata, about half of the total Ca was found in the bark. 3.7. Magnesium The response of Mg accumulation to effluent irrigation varied between the three species (Fig. 4e). In year 1, effluent irrigation retarded Mg accumulation in E. botryoides, had no effect in E. ovata, and enhanced it slightly in E. globulus. By year 2, effluent irrigation retarded Mg accumulation only in E. ovata, and had no effect in E. botryoides and E. globulus. At the end of the
3-year period, the irrigation had significantly retarded Mg accumulation in E. globulus and E. botryoides, but not in E. ovata due to significantly less biomass accumulation in its stands without irrigation (Fig. 2d). Proportionally, less Mg was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides (Fig. 3f). Bark contained more than 25% of the total Mg, but not for E. botryoides without irrigation which had only 13%. 3.8. Manganese Effluent irrigation significantly enhanced Mn accumulation in all three species (Fig. 4f). At the end of the 3-year period, E. globulus accumulated significantly more Mn than the other two species either without
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irrigation or irrigated with effluent. There was no difference between E. botryoides and E. ovata. Approximately half of the total Mn was stored in the foliage of the trees without irrigation (Fig. 3g). Less than 15% of total Mn was found in the wood in all species.
4. Discussion 4.1. Biomass accumulation Neenan and Steinbeck (1979) concluded that differences in biomass yields and ecological tolerances are likely to be more important in species selection for energy crops than variations in their heating values. Therefore, species selection should be mainly based on the biomass yields and ecological tolerances for a specific site or special management considerations, such as effluent irrigation supplying nutrients and water in the current study. Boardman et al. (1996) identified E. globulus to be the preferred species for short-rotation pulpwood, being highly productive and retaining high levels of foliar N and P. In the current study, E. globulus produced the highest levels of biomass and retained the greatest quantities of six nutrients of the three species studied (Tables 2 and 3, Figs. 2 and 3). It is therefore recommended as a suitable species for short rotation forests either without irrigation or irrigated with effluent. The other two species evaluated may be suitable in longer rotations since their current annual increment (CAI) rose sharply in the third year, but E. ovata should only be used in plantations irrigated with effluent because of its poor performance in the stands without irrigation. E. botryoides was infested by Ophelinus eucalypli, which could be the main reason for its poorer performance in the current study than in a previous study at the same site (Barton, cited in Knight and Nicholas (1996)). The highest biomass production and nutrient uptake in E. globulus stands was matched by its denser juvenile foliage. Hillis (1990) indicated that early investment in leaf area, and thus maximum light interception by the Symphomyrtus sub-genus leads to a more rapid increase in canopy photosynthesis than with the Monocalyptus sub-genus. Even within the Symphomyrtus sub-genus, the species with denser juvenile foliage, such as E. globulus, should be selected to give the greatest initial biomass production in short rotation forests. Fertilization and irrigation may be required to sustain high production if plantations are not linked with effluent land treatment systems. Sachs et al. (1980) indicated that Eucalyptus species are prime candidates for woody biomass plantations because of their rapid growth rate, and biomass accumulation being as high as 40 OD t/ha/y on a wide range of sites. However, the growth rate was highly related to
species (including cultivar, family and clone), climate, and management (including fertilization, irrigation, rotation length, and site preparation). In Australia, Cromer et al. (1976) found that the total above-ground biomass of E. globulus (2196 stems/ha) ranged from 1 OD t/ha without fertilizer to 9 OD t/ha following the heaviest application rate (N 202 kg/ha, P 90 kg/ha) at age 2, and 6 OD t/ha to 30 OD t/ha at age 4. Wise and Pitman (1981) reported that above-ground biomass from six Eucalyptus species grown in 10-year rotations ranged from 110 to 162 OD t/ha, mean annual increment (MAI) from 11 to 16 OD t/ha/y. High MAIs have been reported from very high density short rotation plantations of 20,000, 30,000 and 40,000 trees/ha giving 16, 21, 19 OD t/ha/y respectively for E. globulus and 20, 20, 22 OD t/ha respectively for E. camaldulensis after 2 years in Europe (Pereira et al., 1996). Dalianis et al. (1996) reported that E. camaldulensis yielded 26 OD t/ha/y at the first 2-year rotation harvest at densities of 10,000–20,000 plants/ha. Ericsson (1994) estimated that the MAI of above-ground biomass from forest crops ranged from 6 to 22 OD t/ha and CAI from 10 to 28 OD t/ha in managed stands (irrigated and treated with liquid fertiliser). In the present study, the MAI ranged from 11 to 24 OD t/ha/y, and the CAI from 15 to 37 OD t/ha/y (Fig. 2d). Maximum biomass yield of 72 OD t/ha after 3 years was comparable with 73 OD t/ha for the same species with irrigation and fertiliser at the same age in Australia (Pereira et al., 1994). In the current study, a low stem wood percentage (28–53%) was found in the biomass accumulation at the end of the 3-year period (Fig. 3a) for rotation length influenced the proportion of woody biomass (Fig. 5). If wood is the main product desired from the system, a longer rotation should be used, e.g. a 15-year rotation of E. globulus yielding 80% of the total above-ground biomass as wood. The shorter the rotation, the more the leaves and branches contributed to the total above-
Fig. 5. Effect of plantation age on the percentage of wood in total above-ground biomass in E. globulus plantations ((r) data from Negi and Sharma (1984); (m) data from George and Varghese (1990); (s) data from the current study).
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ground biomass. Proportionally, less stem wood in the total above-ground biomass is a characteristic of a short rotation forest. Even though Dalianis et al. (1996) reported the stem percentages increased from first to third rotation following coppicing, other tree parts would still contribute a lot to the harvestable biomass, especially if irrigated with effluent. The reported heating values of eucalypt branches (18.4–19.5 MJ/kg) are similar to those of its stem wood (18.8–19.5 MJ/kg) (Frederick et al., 1985; Dalianis et al., 1996). However for leaves there are conflicting results: Dalianis et al. (1996) reported 16.0 MJ/kg whereas Frederick et al. (1985) reported 21.3–24.1 MJ/kg. In the current study, the heating value of the wood component would be still under half the heating value of the total biomass even calculated using the lower leaf heating values. Therefore, an energy conversion system should utilize all tree parts, including stem, branches and foliage from harvesting short rotation forests. 4.2. Nutrient accumulation Although E. globulus biomass accumulation under effluent irrigation in the current study was similar to results for this species at same age with irrigation and fertiliser in Australia (Pereira et al., 1994), the N accumulation (651 kg N/ha) was much higher than their results (229 kg N/ha). However, the current results were comparable with 239–639 kg/ha N accumulation in 3year old E. botryoides and E. ovata either without irrigation or irrigated with meatworks effluent at the same site (Barton, cited in Knight and Nicholas (1996)). The mean annual N accumulation in the current study ranged from 82 to 217 kg N/ha/y, with the current annual N accumulation ranging from 93 to 321 kg N/ha/y (Fig. 4a). These were higher than Ericsson’s (1994) results of 26–130 kg N/ha/y from managed eucalypt stands. For all three species irrigated with effluent, the Mn accumulation at the end of the 3-year period was around twice that in trees without irrigation (Fig. 4f). However, the total Mn input to the site via the effluent irrigation was only 12 kg/ha over the 3 years (4 kg/ha/y). Therefore, effluent irrigation somehow increased tree Mn uptake from the soil reserves rather than from the effluent source. Haynes and Swift (1985) reported that CaCl2 - and HCl-extractable Mn showed broadly similar trends, both increasing markedly as the pH was lowered. As a result, the concentration of Mn and plant biomass in highbush blueberry plants (Vaccinium corymbosum L. cv. Blueray) increased significantly. Therefore, the higher Mn accumulation in the trees irrigated with effluent in the current study could be caused by a reduction of soil pH from 4.8 to 4.0 after the 3-year effluent irrigation (Guo, 1998).
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Nutrient uptake in very young plantations of any species is low because they do not fully occupy the site (Brockway et al., 1982). In the current study, less biomass and nutrient accumulation were found in the first year (Tables 2 and 3, Figs. 2 and 4). Therefore, less effluent should be applied during the first year after the trees have been planted since the nutrient and water consumption is correlated to the growth rate. However, E. globulus stands irrigated with effluent were able to accumulate as much as 104 kg N/ha N in the first year (Fig. 4a). 4.3. Leaf biomass and nutrient accumulation in foliage The major effect of improved nutrient and water availability in the soil is to enhance foliage growth which includes larger leaves as well as more leaves per plant, thereby increasing light interception (Pereira et al., 1989). Usually, the greater the LAI and leaf biomass, the more the total biomass production because leaf is the unit for primary production. In the current study, even though effluent irrigation increased the total aboveground biomass accumulation (Table 2, Fig. 2d), it reduced the leaf proportion of the biomass (Fig. 3a) and tended to reduce LAI (Table 2) but with some exceptions (Fig. 2c). Total net leaf biomass production should include both the leaf biomass on the trees at harvest, and the fallen leaves. More litter fall was found in stands irrigated with effluent, which was consistent across all three species (Guo, 1998). This was possible due to leaf longevity having been reduced when faster tree growth was achieved after effluent was applied. In addition, more branch biomass was found in the stands irrigated with effluent (Fig. 3a), which should support more leaves though some leaves may only live for a short time. Escudero et al. (1992) indicated that the lower the nutrient status of a species the longer the life-span of its leaves. Contrarily, the higher the nutrient status, as in the current study, the shorter the leaf life-span expected. The results from single leaf monitoring indicated that a shorter leaf life occurred on trees irrigated with effluent (Guo, 1998). Therefore, leaf longevity could play a very important role for the trees irrigated with effluent with lower leaf biomass. Manganese toxicity is a major factor limiting plant growth in acidic soils (Foy et al., 1978; Sumner et al., 1991). Leaf shedding results from Mn toxicity for some plant species, e.g. satsuma mandarin (Citrus unshiu Marc.), potato (Solanum tuberosum L.) and cowpea (Vigna unguiculata (L.) Walps.) (Horst, 1988). In the current study, the shorter leaf life and higher litter fall from trees irrigated with effluent could also be caused by more Mn accumulation in the leaf, though light competition after canopy closure may also play some role in it.
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Excess Mn in leaves can cause a decline in photosynthesis in trees (Kitao et al., 1997) and also in other plants, such as tobacco (Nicotiana tabacum L.) (Nable et al., 1988). In the current study however, irrigated eucalypt species grew particularly well, even though the trees had less living leaf than the trees without irrigation. The higher biomass gave no evidence of any photosynthesis decline. Hence, eucalypt species may have relatively high Mn tolerance. Bargali et al. (1992) found foliage was the largest component of nutrient storage although its contribution decreased with age for E. tereticornis plantations at 2–8 years old in Central Himalaya. The relative contribution to the proportion of nutrients in different above-ground components was generally in the order: foliage > bole ðwood þ barkÞ > branch > twig > reproductive parts. Similar results were also found in the current study (Fig. 3), but the leaf contribution decreased only marginally with age during the 3-year period (data not shown). The shorter the rotation, the more the foliage contributes to the total above-ground biomass. Leaves have a short life. Therefore, their harvesting and removal from the site should be a major consideration for crop production and sustainable land use. In effluent land treatment systems, it is necessary to remove foliage frequently for preventing excessive nutrient return from the litter fall. Overall, the design and management of a short rotation forest should be based on its main objective and related to the nutrient cycling within the system. If the short rotation forest is grown solely for energy biomass production, then a species, variety, family or clone with fast growth, high yields and high nutrient use efficiency should be selected. Only the tree parts with high nutrient use efficiency, such as the stemwood, should be removed from the site so that less nutrients will need to be replaced by use of commercial fertilizers. When a short rotation forest is grown to strip nutrients in a land treatment system, the species, variety, family or clone with high growth rates, but with a low nutrient use efficiency should be selected. All above-ground tree parts should be harvested and removed from the site.
5. Conclusions It is important that the correct tree species is selected to achieve maximum biomass production for a given site, and, in the case of a land treatment system, maximise nutrient uptake. Using eucalyptus in a short rotation forest linked with effluent land treatment was a good choice as their growth was not adversely affected by the soil pH reduction which resulted from effluent application. E. globulus showed optimal potential in energy short rotation forests, whether linked with ef-
fluent land treatment or not. To maximize nutrient removal from the site in an effluent land treatment system, the whole of the above-ground biomass should be harvested and removed for energy conversion. Less effluent should be applied in very young plantations.
Acknowledgements The Richmond Meat Processors & Packers Ltd. processing plant at Oringi, and Gary Newnham, a chief engineer, are thanked for their assistance and the permission to undertake the research work on their site.
References Bargali, S.S., Singh, R.P., Singh, S.P., 1992. Structure and function of an age series of eucalypt plantations in Central Himalaya. II. Nutrient dynamics. Ann. Bot. 69, 413–421. Boardman, R., Shaw, S., McGuire, D.O., Ferguson, T., 1996. Comparison of crop foliage biomass, nutrient contents and nutrient-use efficiency of crop biomass for four species of Eucalyptus and Casuarina glauca irrigated with secondary sewage effluent from Bolivar, South Australia. In: Polglase, P.J., Tunningley, W.M. (Eds.), Land Application of Wastes in Australia and New Zealand: Research and Practice (Australian Conference 29 September–4 October 1996). CSIRO Forestry & Forest Products on behalf of the NZ Land Treatment Collective, pp. 147–158. Brockway, D.G., Burton, T.M., Cooley, J.H., D’Itri, F.M., Dowdy, R.H., Ellis, B.G., Epstein, L., Erickson, A.E., Hook, J.E., Jacobs, L.W., Kerr, S.N., Knezek, B.D., Myers, E.A., Palazzo, A.J., Poloncsik, S., Safir, G.R., Sopper, W.E., Sutherland, J.C., Tesar, M.B., Thomas, R.E., Urie, D.H., 1982. The current status on the selection and management of vegetation for slow rate and overland flow application systems to treat municipal wastewater in the North Central Region of the United States. In: D’Itri, F.M. (Ed.), Land Treatment of Municipal Wastewater––Vegetation Selection and Management. Ann Arbor Science, Publishers INC/The Butterworth Group, Ann Arbor, MI/London, pp. 5–18. Cromer, R.N., Raupach, M., Clarke, A.R.P., Cameron, J.N., 1976. Eucalypt plantations in Australia––the potential for intensive production and utilization. In: OSLO Biomass Studies. College of Life Sciences and Agriculture, University of Maine at Orono, pp. 29–40. Dalianis, C., Djouras, N., Sooter, C., 1996. Very short rotation and dense eucalypt plantations for energy. In: Chartier, P., Ferrero, G.L., Henius, U.M., Hultberg, S., Sachau, J., Wiinblad, M. (Eds.), Proceedings of the Ninth European Bioenergy Conference on Biomass for Energy and the Environment, Copenhagen, Denmark 24–27 June 1996. Pergamon, New York, pp. 725–732. Ericsson, T., 1994. Nutrient dynamics and requirements of forest crops. NZ J. For. Sci. 24 (2/3), 133–168. Escudero, A., Del Arco, J.M., Sanz, I.C., Ayala, J., 1992. Effects of leaf longevity and retranslocation efficiency on the retention time of nutrients in the leaf biomass of different woody species. Oecologia 90, 80–87. Foy, C.D., Chaney, R.L., White, M.C., 1978. The physiology of metal toxicity in plants. Annu. Rev. Plant Physiol. 29, 511–566. Frederick, D.J., Madgwick, H.A.I., Jurgensen, M.F., Oliver, G.R., 1985. Dry matter, energy, and nutrient contents of 8-year-old stands of Eucalyptus regnans, Acacia dealbata, and Pinus radiata in New Zealand. NZ J. For. Sci. 15 (2), 142–157.
L.B. Guo et al. / Bioresource Technology 85 (2002) 273–283 George, M.R., Varghese, G., 1990. Nutrient cycling in Eucalyptus globulus plantation I. Organic matter production, nutrients accumulation in standing crop and nutrients removal through harvest. Indian For. 116 (1), 42–48. Guo, L.B., 1998. Nutrient Cycling in Eucalyptus Short Rotation Forests––Sustainable Production Linked with Meatworks Effluent Land Treatment. Ph.D. Thesis. Massey University, Palmerston North, New Zealand, p. 263. Haynes, R.J., Swift, R.S., 1985. Effects of soil acidification on the chemical extractability of Fe, Mn, Zn and Cu and the growth and micronutrient uptake of highbush blueberry plants. Plant Soil 84, 201–212. Heilman, P., 1992. Sustaining production: nutrient dynamics and soils. In: Mitchell, C.P., Ford-Robertson, J.B., Hinckley, T., SennerbyForsse, L. (Eds.), Ecophysiology of Short Rotation Forest Crops. Elsevier Applied Science, London, pp. 216–230. Hillis, W.E., 1990. Fast growing eucalyptus and some of their characteristics. In: Werner, D., Muller, P. (Eds.), Fast Growing Trees and Nitrogen Fixing Trees. Gustav Fischer Verlag, Stuttgart, New York, pp. 184–193. Horst, W.J., 1988. The physiology of manganese toxicity. In: Graham, R.D., Hannam, R.J., Uren, N.C. (Eds.), Manganese in Soils and Plants. Kluwer Academic Publishers, Dordrecht, pp. 175–188. Kitao, M., Lei, T.T., Koike, T., 1997. Effects of manganese toxicity on photosynthesis of white birch (Betula platyphylla var. japonica) seedlings. Physiol. Plant 101, 249–256. Knight, P.J., Nicholas, I.D., 1996. Eucalypt nutrition: New Zealand experience. In: Attiwill, P.M., Adams, M.A. (Eds.), Nutrition of Eucalyptus. CSIRO, Australia, pp. 275–302. Marecos do Monte, H., Silva e Sousa, M., Silva Neves, A., 1989. Effects on soil and crops of irrigation with primary and secondary effluents. Water Sci. Technol. 21, 427–434. Nable, R.O., Houtz, R.L., Cheniae, G.M., 1988. Early inhibition of photosynthesis during development of Mn toxicity in tobacco. Plant Physiol. 86, 1136–1142. National Resources Survey, 1971. National Resources Survey (part vi)––Hawke’s Bay Region. Government Printer, Wellington, New Zealand, p. 223. Neenan, M., Steinbeck, K., 1979. Caloric values for young sprouts of nine hardwood species. For. Sci. 25 (3), 455–461.
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Negi, J.D.S., Sharma, D.C., 1984. Distribution of nutrient in an age series of Eucalyptus globulus plantation in Tamil Nadu. Indian For. 110, 944–953. Newbould, P.J., 1967. Methods for Estimating the Primary Production of Forests. Willmer Brothers Limited, Birkenhead, Great Britain, p. 60. Parde, J., 1980. Forest biomass. Forestry Abstracts 41 (8), 343–362. Pereira, J.S., Linder, S., Araujo, M.C., Pereira, H., Ericsson, T., Borralho, N., Leal, L.C., 1989. Optimization of biomass production in Eucalyptus globulus plantations. In: Pereira, J.S., Landsberg, J.J. (Eds.), Biomass Production by Fast-Growing Trees. Kluwer Academic Publishers, Dordrecht, pp. 101–121. Pereira, J.S., Linder, S., Araujo, M.C., Tome, M., Madeira, M.V., Ericsson, T., 1994. Biomass production with optimized nutrition in Eucalyptus globulus plantations. In: Pereira, J.S. (Ed.), Eucalyptus for Biomass Production, pp. 13–30. Pereira, H., Pardos, J., Boudet, A.M., Mitchell, O., Mughini, G., Kyritsis, S., Dalianis, C., 1996. Eucalypt plantations for production of raw-material for industry and energy in Europe. In: Chartier, P., Ferrero, G.L., Henius, U.M., Hultberg, S., Sachau, J., Wiinblad, M. (Eds.), Proceedings of the Ninth European Bioenergy Conference on Biomass for Energy and the Environment, Copenhagen, Denmark 24–27 June 1996. Pergamon, New York, pp. 84– 89. Sachs, R.M., Gilpin, D.W., Mock, T., 1980. Yields of short rotation Eucalyptus grandis in high density plantings. In: Energy from Biomass and Wastes IV (Symposium Papers Presented January 21– 25, 1980, Florida). Institute of Gas Technology, USA, pp. 107–114. SAS Institute, 1990. SAS/STAT User’s Guide (Version 6). SAS Institute, Cary, NC. Sumner, M.E., Fey, M.V., Noble, A.D., 1991. Nutrient status and toxicity problems in acid soils. In: Ulrich, B., Sumner, M.E. (Eds.), Soil Acidity. Springer-Verlag, Berlin, pp. 149–182. Wise, P.K., Pitman, M.G., 1981. Nutrient removal and replacement associated with short-rotation eucalypt plantations. Aust. For. 44 (3), 142–152. Young, H.E., Carpenter, P.N., 1976. Sampling variation of nutrient element content within and between trees of the same species. In: Oslo Biomass Studies. College of Life Science and Agriculture, University of Maine at Orono, pp. 77–99.
Biomass production and nutrient cycling in Eucalyptus short rotation energy forests in New Zealand. I: biomass and nutrient accumulation L.B. Guo a
a,*
, R.E.H. Sims a, D.J. Horne
b
Institute of Technology and Engineering, Massey University, Private Bag 11 222, Palmerston North, New Zealand b Institute of Natural Resources, Massey University, Private Bag 11 222, Palmerston North, New Zealand Received 28 March 2001; received in revised form 22 April 2002; accepted 4 May 2002
Abstract Accumulation of biomass and nutrients (N, P, K, Ca, Mg and Mn) was measured during the first 3-year rotation of three Eucalyptus short rotation forest species (E. botryoides, E. globulus and E. ovata) irrigated with meatworks effluent compared with no irrigation. E. globulus had the highest biomass and nutrient accumulation either irrigated with effluent or without irrigation. After 3year growth, E. globulus stands irrigated with effluent accumulated 72 oven dry t/ha of above-ground total biomass with a total of 651 kg N, 55 kg P, 393 kg K, 251 kg Ca, 35 kg Mg and 67 kg Mn. Effluent irrigation increased the accumulation of biomass, N, P, K and Mn, but tended to reduce the leaf area index and leaf biomass, and decreased the accumulation of Ca and Mg. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biomass; Nutrients; Accumulation; Eucalyptus; Short rotation forest; Effluent land treatment
1. Introduction Short rotation forests are a renewable source of energy and can reduce the energy demands currently met by fossil fuels. However, much of the concern about the sustainability of short rotation forest systems focuses on the question of depletion of soil nutrients. This is heightened by the harvesting of whole-trees together with the short harvest cycles (Heilman, 1992; Ericsson, 1994). For sustainable land use, the nutrient loss must be remedied by application of fertilisers, which usually increases the input costs and hence the energy cost from the biomass. Effluent from meatworks contains nutrients which could replace commercial fertilizer to provide nutrients as well as water for crop production (Marecos do Monte et al., 1989). Land treatment by applying the effluent to the soil would avoid disposal to the environment using waterways. In this case, frequent harvesting of the trees * Corresponding author. Present address: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia. Tel.: +61-2-62465267; fax: +61-2-6246-5000. E-mail address: [email protected] (L.B. Guo).
to remove large quantities of nutrients from the soil is essential for sustainable land use. In short rotation forest production systems, either linked with effluent land treatment or without, harvestable biomass and nutrients accumulated in the biomass are closely related to the end products and the nutrient removal from the systems. During tree growth, part of the above-ground biomass produced and nutrient uptake is returned to the soil surface via litter fall. The accumulation of biomass and nutrients is usually defined as above-ground biomass and nutrients in the standing trees, which are the parts of trees normally to be removed from the site. The overall aim of this study was to determine the flow of nutrients within eucalypt short rotation forest ecosystems, and provide information for the effective management of the systems, especially when linked with effluent land treatment. The specific objectives of the current part of this paper were to determine: (i) the biomass accumulation and the potential nutrient removal following whole tree harvesting of three selected eucalypt species during the first 3-year rotation of short rotation forests irrigated with meatworks effluent and without irrigation; and (ii) the distribution of biomass
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and nutrients in the standing trees at the end of the rotation.
2. Methods 2.1. Site, species and experimental design The study site was at the Richmond Meat Processors & Packers Ltd.’s processing plant at Oringi, which is adjacent to the Manawatu River, located near Dannevirke, New Zealand. Longitude is 176°010 E and latitude is 40°160 S. Monthly distributions of rainfall and temperature for 10-year averages (1986–1996) are shown in Fig. 1. The soils are Dannevirke-Kopua soils from alluvial deposits, and having textures of sandy loam overlying stony gravels with mostly medium to low natural fertility (National Resources Survey, 1971). Before the trees were planted, the site was occupied by pasture, which had been irrigated with meatworks effluent for 12 years. Three-month-old seedlings grown in root trainers were planted for 30 hectares in December 1993 at a density of 4167 stems/ha (1 m 2:4 m spacing). A split block experimental design was used with three blocks in the plantation. In each block, there were three subblocks of species, Eucalyptus botryoides (B), E. globulus (G), and E. ovata (O). Each sub-block was split into two plots for the treatments: without irrigation (N) and irrigated with effluent (I). Each of the 18 plots was 10 m 10 m, giving 40 trees per plot, and with a 10 m buffer zone between them. Next to each plot, a same size plot was established for mean tree sampling when the trees were 1 and 2 years old. Effluent from the meatworks (mixture of wastewater from stockyards, slaughter floor, casing and offal, pelt wash, etc.), stored in an anaerobic pond, was irrigated onto the plots at a rate of 20 mm/week using flood channels between the rows of trees planted on 100 mm high ridges. The chemical and biochemical characteris-
Table 1 Chemical composition of the effluent from the anaerobic pond of the Richmond meatworks at Oringi, Dannevirke, New Zealand Biochemical oxygen demand (g/m3 ) Chemical oxygen demand (g/m3 ) Total Kjeldahl nitrogen (g/m3 ) Ammoniac nitrogen (g/m3 ) Nitrate nitrogen (g/m3 ) Phosphorus (g/m3 ) Potassium (g/m3 ) Calcium (g/m3 ) Magnesium (g/m3 ) Manganese (g/m3 ) pH
400 1060 200 150 <0.2 20 90 25 7 0.4 6.8
tics of the effluent are shown in Table 1. The planned rotation length between coppice harvests was 3 years, but this study was conducted during the first rotation from 1994 to 1996. 2.2. Measurements and sampling Tree diameters, heights, and sampling of tree biomass were measured in December 1994, December 1995, and December 1996 when the trees were 1, 2 and 3 years old. Tree diameters were measured at ground level as they were 1 year old, but at breast height (1.4 m) thereafter. The mean tree method was used for destructive sampling as the mean basal area seems to be the best method for biomass estimation in even-aged stands of a single species (Parde, 1980). The mean trees were accessed according to tree mean height, and their mean diameter calculated from the mean basal area in each plot with account also being taken of the crown width. Three mean trees determined was selected and harvested in the same treatment plot next to each plot when the trees were 1 and 2 years old, while the mean trees for the final sampling were selected and harvested within each plot when the trees were 3 years old. The whole mean trees above-ground were harvested and stored in a cool room before processing. 2.3. Laboratory analyses
Fig. 1. Monthly rainfall and mean temperature for Dannevirke, New Zealand (10-year average from 1986 to 1996).
The mean trees were divided into five components: foliage, twig (<6.4 mm diameter), branch (6.5–25.4 mm diameter), bark and wood from stem and branches larger than 25.4 mm (Young and Carpenter, 1976). New soft shoots with young leaves not fully open and dead portions (including dead bark, twigs, branches, and leaves) were separated to give a total of seven categories. The size of the photosynthetic system was the leaf area index (LAI) being the area of leaves carried above a unit area of ground (Newbould, 1967). LAI was estimated from leaf biomass using a weight/leaf area conversion factor determined from a sub-sample of the leaves, their
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area was measured using a leaf area meter (LI-Cor LI3100). Samples of all tree parts were weighed after being oven dried at 80 °C to constant weight and then were ground to pass through a 1 mm sieve for nutrient analyses. Total N and total P were analysed using a Technicon Auto Analyser (Pulse Instrumentation Ltd., Saskatoon, Canada) following Kjeldahl digestion. K, Ca, Mg and Mn were analyzed using an atomic absorption spectroscopy (GBC 904 AA) following nitric acid digestion. Total oven dry (OD) biomass was obtained from the mean basal area of the trees in the plots and the sample trees as follows: P WT WP ¼ AP P AT
acted on the effects, but with some exceptions (Table 2). In the first year, effluent irrigation increased tree stem diameter at ground level (DG) in E. globulus but had no effects on the other two species (Fig. 2a). By year 2 and year 3, it increased the diameter at breast height (DBH) in all three species, except E. globulus at the end of the 3-year period. E. globulus irrigated with effluent produced the greatest DG in the first year, and E. botryoides the smallest. The DBH was larger in E. globulus and E. botryoides irrigated with effluent in the second year. At the end of the rotation, E. ovata irrigated with effluent caught up to E. globulus. The smallest DBH was found in both E. botryoides and E. ovata without irrigation.
where WP is the plot biomass (OD t/ha), AP is the plot basal area (m2 /ha), WT is the sample tree biomass (OD t/ tree), and AT is the sample tree basal area (m2 ). Nutrients accumulated in each tree component were estimated as follow:
Table 2 Tree performance and biomass accumulation of three eucalypt species (B ¼ E: botryoides; G ¼ E: globules; O ¼ E: ovata) in short rotation forests without irrigation (C) and irrigated with effluent (E)
NC ¼ 1000CN WC where NC is the nutrient accumulation (kg/ha) for each tree component in each plot, CN is the nutrient concentration (%) of the tree component, WC is the total biomass of the tree component (OD t/ha). Total nutrient accumulation in the standing trees was estimated from the nutrient accumulation in each of the tree components: n X NP ¼ Ni
Age Diameter (cm) (at ground level when 1 year old, and at breast height when P2 year old)
1
2
3
Species n ¼ 240
B G O LSD0:05
3.2 4.5 4.3 0.3
5.0 6.1 4.9 0.4
6.7 7.9 6.9 0.8
Treatment n ¼ 360
C E LSD0:05
3.8 4.1 0.1
5.0 5.6 0.5
6.8 7.5 0.7
Interaction Height (m)
Species n ¼ 240
B G O LSD0:05
1.3 1.9 2.0 0.2
2.4 4.9 4.3 0.5
4.5 7.0 5.8 0.6
Treatment n ¼ 360
C E LSD0:05
1.6 1.9 0.2
3.7 4.0 0.2
5.6 5.8 ns
1
where NP is plot nutrient accumulation (kg/ha), Ni is the nutrient accumulation in each tree component in each plot (kg/ha), n ¼ 7 (the number of tree components). 2.4. Statistical analysis All data from the split block design experiment were analysed using the SAS GLM procedure (SAS Institute, 1990). The model of a 2-factorial combination with 3 repeat measurements (year) was used for analysing the data of tree performance (diameter, height and LAI), biomass accumulation, and nutrient accumulation. Means were separated by the least significant difference (LSD) test when species, treatments and their interactions were significant (P < 0:05).
3. Results 3.1. Tree performance and biomass accumulation Species and treatment significantly affected tree performance and biomass accumulation, and they inter-
Interaction LAI (m2 /m2 )
Species n¼6
B G O LSD0:05
0.3 1.4 1.6 0.2
0.9 6.8 5.4 0.5
4.6 5.4 2.8 0.6
Treatment n¼9
C E LSD0:05
1.2 1.0 0.1
4.1 2.9 0.8
4.6 3.9 0.5
Interaction Biomass (OD t/ha)
Species n¼6
B G O LSD0:05
1.9 6.0 5.3 1.1
7.7 32.2 20.9 4.9
39.7 64.7 45.5 5.8
Treatment n¼9
C E LSD0:05
4.3 4.4 ns
17.5 22.9 4.3
42.4 57.5 6.9
Interaction ns denotes not significant. * P < 0:01. ** P < 0:05. *** P < 0:001.
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Fig. 2. Tree performance and biomass accumulation in eucalypt plantations: (a) diameter (at ground level when 1 year old and at breast height when P 2 years old), (b) height, (c) LAI and (d) biomass accumulation (N ¼ without irrigation; I ¼ irrigated with effluent; B ¼ E: botryoides; G ¼ E: globulus; O ¼ E: ovata; n ¼ 120, but 3 for LAI and biomass; vertical bars indicate LSD0:05 ).
E. globulus was the tallest species, and E. botryoides was the shortest during the 3-year period (Fig. 2b). Effluent irrigation increased tree height throughout the 3year period for E. botryoides, but by year 1 and year 3 for E. ovata, and by year 1 and year 2 for E. globulus. E. globulus trees without irrigation were taller than its trees irrigated with effluent at the end of the 3-year period. Effluent irrigation reduced LAI during the 3-year period except for E. botryoides at year 2, and for E. globulus at years 1 and 3 (Fig. 2c). There were significant differences in the LAI between the three species, except for E. globulus and E. ovata irrigated with effluent at year 1, and E. botryoides without irrigation and E. globulus at year 3. Relatively little biomass was accumulated in the first year (Table 2, Fig. 2d). There were significant differences in the above-ground biomass accumulation between the three species. E. globulus showed the best growth performance in the three studied species, either without irrigation or irrigated with effluent. At the end of the 3year period, 72 OD t/ha of above-ground biomass were accumulated in its stands irrigated with effluent. Effluent irrigation significantly increased the biomass accumulation in all three species after 2 and 3 years. At the end of the 3-year period, effluent application increased the total above-ground biomass accumulation by 19%, 24%
and 76% for E. botryoides, E. globulus and E. ovata, respectively. The response of E. ovata to effluent was significantly greater than that of the other two species. The distribution of biomass in the various tree components was also affected by effluent irrigation (Fig. 3a). Proportionally, less foliage biomass was found in the trees irrigated with effluent than in the trees without irrigation, but there were more twigs and branches. More wood was found in the trees irrigated with effluent than in the trees without irrigation, except for E. globulus, for their diameters were smaller and tree heights were lower than for trees without irrigation (Fig. 2). Overall, approximately half of the biomass was wood except in E. botryoides without irrigation (28%). 3.2. Nutrient accumulation Species and treatment significantly affected nutrient accumulation and they interacted on the effects even though there were some exceptions (Table 3). 3.3. Nitrogen There were significant differences in N accumulation between the three species, the trend being similar to the biomass accumulation (Table 3, Fig. 4a). Less N was
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Fig. 3. Biomass and nutrient distribution in the harvestable above-ground biomass components at the end of the 3-year period: (a) biomass, (b) N, (c) P, (d) K, (e) Ca, (f) Mg, and (g) Mn (the area of each chart depicts the comparative total biomass or nutrient accumulation).
accumulated in E. botryoides during the first 2 years, but by year 3 this species had accumulated around 400 kg/ha and caught up with E. globulus without irrigation and E. ovata irrigated with effluent. By the end of the 3-year period, E. globulus irrigated with effluent had accumu-
lated the greatest amount of N, and E. ovata without irrigation the least. The N distribution in the tree components was affected by the effluent irrigation (Fig. 3b). Proportionally, less N was found in the foliage of trees irrigated with
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Table 3 Nutrient accumulation (kg/ha) of three eucalypt species (B ¼ E: botryoides; G ¼ E: globules; O ¼ E: ovata) in short rotation forests without irrigation (C) and irrigated with effluent (E) Age N
21.0 80.9 69.5 15.9
87.6 285.8 166.4 53.1
406.9 541.3 322.8 58.6
Treatment n¼9
C E LSD0:05
50.3 63.9 9.6
154.0 205.8 42.3
355.2 492.2 76.4
Species n¼6
B G O LSD0:05
3.0 6.7 5.2 1.2
7.2 26.0 15.4 5.5
39.6 44.8 25.8 12.5
Treatment n¼9
C E LSD0:05
4.7 5.1 ns
12.5 19.9 2.3
28.7 44.6 19.2
Species n¼6
B G O LSD0:05
14.3 49.0 50.9 12.1
61.3 222.3 152.4 26.2
229.6 327.8 267.1 54.3
Treatment n¼9
C E LSD0:05
34.0 42.1 6.1
130.4 160.2 29.2
213.9 335.7 74.6
Interaction Ca
Species n¼6
B G O LSD0:05
21.4 97.1 36.5 9.7
43.7 117.8 173.0 53.1
235.3 291.9 233.4 58.6
Treatment n¼9
C E LSD0:05
65.9 37.4 10.5
136.4 86.6 42.3
302.1 204.9 76.4
Interaction Mg
Species n¼6
B G O LSD0:05
2.4 8.2 5.3 1.8
7.1 21.5 14.7 5.5
32.7 40.3 28.4 12.5
Treatment n¼9
C E LSD0:05
5.5 5.1 0.3
16.0 12.9 2.3
36.6 31.0 ns
B G O LSD0:05
1.1 4.9 3.6 0.9
7.8 23.1 15.2 6.2
29.9 47.7 27.9 14.3
C E LSD0:05
2.5 3.8 1.1 ns
9.9 20.8 9.2 ns
21.8 48.5 14.3
Interaction Mn
3
B G O LSD0:05
Interaction K
2
Species n¼6
Interaction P
1
Species n¼6
Treatment n¼9 Interaction ns denotes not significant. * P < 0:05. ** P < 0:01. *** P < 0:001.
effluent than those without irrigation, and more was found in the twigs, branches and wood. Overall, less than one quarter of the total N was accumulated in the wood for all three species. 3.4. Phosphorus There were significant differences in P accumulation between the three species (Table 3, Fig. 4b). Less P was accumulated in E. botryoides in the first 2 years. In the third year, the accumulation of P in this species reached approximately 40 kg/ha and caught up with E. globulus without irrigation and E. ovata irrigated with effluent. At the end of the rotation, E. globulus trees irrigated with effluent accumulated the greatest amount of P, and E. ovata without irrigation accumulated the least, where little net P accumulation occurred during the third year. The P distribution in the various tree components was also affected by the effluent irrigation (Fig. 3c). Proportionally, less P was found in foliage of the trees irrigated with effluent than in that of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides. More P was found in the wood of trees irrigated with effluent than in the wood of trees without irrigation except in E. globulus. 3.5. Potassium There were significant differences in K accumulation between the three species (Table 3, Fig. 4c). Effluent irrigation only enhanced K accumulation in E. globulus at first, then in E. botryoides in the second year. By year 3, effluent irrigation significantly enhanced K accumulation in all three species. During the third year, no net K accumulation occurred in E. ovata without irrigation, but a significant amount was accumulated in E. ovata irrigated with effluent which caught up with E. globulus irrigated with effluent. Proportionally, less K was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides (Fig. 3d). More K was found in the wood of the trees irrigated with effluent than in the trees without irrigation, but not for E. globulus. 3.6. Calcium Effluent irrigation retarded Ca accumulation in all three species although it increased the biomass accumulation (Fig. 4d). Ca was accumulated in E. ovata without irrigation most sharply in the second year and in E. botryoides without irrigation in the third year. The final accumulation over the 3-year period was greatest for E. globulus and E. botryoides without irrigation.
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279
Fig. 4. Nutrient accumulation in eucalypt plantations over the 3-year period: (a) N, (b) P, (c) K, (d) Ca, (e) Mg, and (f) Mn (N ¼ without irrigation; I ¼ irrigated with effluent; B ¼ E: botryoides; G ¼ E: globulus; O ¼ E: ovata; vertical bars indicate LSD0:05 ; n ¼ 3).
Proportionally, less Ca was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the barks (Fig. 3e). Approximately double Ca was stored in the wood of the trees irrigated with effluent than in the trees without irrigation, except for E. globulus. In E. ovata, about half of the total Ca was found in the bark. 3.7. Magnesium The response of Mg accumulation to effluent irrigation varied between the three species (Fig. 4e). In year 1, effluent irrigation retarded Mg accumulation in E. botryoides, had no effect in E. ovata, and enhanced it slightly in E. globulus. By year 2, effluent irrigation retarded Mg accumulation only in E. ovata, and had no effect in E. botryoides and E. globulus. At the end of the
3-year period, the irrigation had significantly retarded Mg accumulation in E. globulus and E. botryoides, but not in E. ovata due to significantly less biomass accumulation in its stands without irrigation (Fig. 2d). Proportionally, less Mg was found in the foliage of the trees irrigated with effluent than in the foliage of the trees without irrigation, but more was found in the twigs and branches except for E. botryoides (Fig. 3f). Bark contained more than 25% of the total Mg, but not for E. botryoides without irrigation which had only 13%. 3.8. Manganese Effluent irrigation significantly enhanced Mn accumulation in all three species (Fig. 4f). At the end of the 3-year period, E. globulus accumulated significantly more Mn than the other two species either without
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irrigation or irrigated with effluent. There was no difference between E. botryoides and E. ovata. Approximately half of the total Mn was stored in the foliage of the trees without irrigation (Fig. 3g). Less than 15% of total Mn was found in the wood in all species.
4. Discussion 4.1. Biomass accumulation Neenan and Steinbeck (1979) concluded that differences in biomass yields and ecological tolerances are likely to be more important in species selection for energy crops than variations in their heating values. Therefore, species selection should be mainly based on the biomass yields and ecological tolerances for a specific site or special management considerations, such as effluent irrigation supplying nutrients and water in the current study. Boardman et al. (1996) identified E. globulus to be the preferred species for short-rotation pulpwood, being highly productive and retaining high levels of foliar N and P. In the current study, E. globulus produced the highest levels of biomass and retained the greatest quantities of six nutrients of the three species studied (Tables 2 and 3, Figs. 2 and 3). It is therefore recommended as a suitable species for short rotation forests either without irrigation or irrigated with effluent. The other two species evaluated may be suitable in longer rotations since their current annual increment (CAI) rose sharply in the third year, but E. ovata should only be used in plantations irrigated with effluent because of its poor performance in the stands without irrigation. E. botryoides was infested by Ophelinus eucalypli, which could be the main reason for its poorer performance in the current study than in a previous study at the same site (Barton, cited in Knight and Nicholas (1996)). The highest biomass production and nutrient uptake in E. globulus stands was matched by its denser juvenile foliage. Hillis (1990) indicated that early investment in leaf area, and thus maximum light interception by the Symphomyrtus sub-genus leads to a more rapid increase in canopy photosynthesis than with the Monocalyptus sub-genus. Even within the Symphomyrtus sub-genus, the species with denser juvenile foliage, such as E. globulus, should be selected to give the greatest initial biomass production in short rotation forests. Fertilization and irrigation may be required to sustain high production if plantations are not linked with effluent land treatment systems. Sachs et al. (1980) indicated that Eucalyptus species are prime candidates for woody biomass plantations because of their rapid growth rate, and biomass accumulation being as high as 40 OD t/ha/y on a wide range of sites. However, the growth rate was highly related to
species (including cultivar, family and clone), climate, and management (including fertilization, irrigation, rotation length, and site preparation). In Australia, Cromer et al. (1976) found that the total above-ground biomass of E. globulus (2196 stems/ha) ranged from 1 OD t/ha without fertilizer to 9 OD t/ha following the heaviest application rate (N 202 kg/ha, P 90 kg/ha) at age 2, and 6 OD t/ha to 30 OD t/ha at age 4. Wise and Pitman (1981) reported that above-ground biomass from six Eucalyptus species grown in 10-year rotations ranged from 110 to 162 OD t/ha, mean annual increment (MAI) from 11 to 16 OD t/ha/y. High MAIs have been reported from very high density short rotation plantations of 20,000, 30,000 and 40,000 trees/ha giving 16, 21, 19 OD t/ha/y respectively for E. globulus and 20, 20, 22 OD t/ha respectively for E. camaldulensis after 2 years in Europe (Pereira et al., 1996). Dalianis et al. (1996) reported that E. camaldulensis yielded 26 OD t/ha/y at the first 2-year rotation harvest at densities of 10,000–20,000 plants/ha. Ericsson (1994) estimated that the MAI of above-ground biomass from forest crops ranged from 6 to 22 OD t/ha and CAI from 10 to 28 OD t/ha in managed stands (irrigated and treated with liquid fertiliser). In the present study, the MAI ranged from 11 to 24 OD t/ha/y, and the CAI from 15 to 37 OD t/ha/y (Fig. 2d). Maximum biomass yield of 72 OD t/ha after 3 years was comparable with 73 OD t/ha for the same species with irrigation and fertiliser at the same age in Australia (Pereira et al., 1994). In the current study, a low stem wood percentage (28–53%) was found in the biomass accumulation at the end of the 3-year period (Fig. 3a) for rotation length influenced the proportion of woody biomass (Fig. 5). If wood is the main product desired from the system, a longer rotation should be used, e.g. a 15-year rotation of E. globulus yielding 80% of the total above-ground biomass as wood. The shorter the rotation, the more the leaves and branches contributed to the total above-
Fig. 5. Effect of plantation age on the percentage of wood in total above-ground biomass in E. globulus plantations ((r) data from Negi and Sharma (1984); (m) data from George and Varghese (1990); (s) data from the current study).
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ground biomass. Proportionally, less stem wood in the total above-ground biomass is a characteristic of a short rotation forest. Even though Dalianis et al. (1996) reported the stem percentages increased from first to third rotation following coppicing, other tree parts would still contribute a lot to the harvestable biomass, especially if irrigated with effluent. The reported heating values of eucalypt branches (18.4–19.5 MJ/kg) are similar to those of its stem wood (18.8–19.5 MJ/kg) (Frederick et al., 1985; Dalianis et al., 1996). However for leaves there are conflicting results: Dalianis et al. (1996) reported 16.0 MJ/kg whereas Frederick et al. (1985) reported 21.3–24.1 MJ/kg. In the current study, the heating value of the wood component would be still under half the heating value of the total biomass even calculated using the lower leaf heating values. Therefore, an energy conversion system should utilize all tree parts, including stem, branches and foliage from harvesting short rotation forests. 4.2. Nutrient accumulation Although E. globulus biomass accumulation under effluent irrigation in the current study was similar to results for this species at same age with irrigation and fertiliser in Australia (Pereira et al., 1994), the N accumulation (651 kg N/ha) was much higher than their results (229 kg N/ha). However, the current results were comparable with 239–639 kg/ha N accumulation in 3year old E. botryoides and E. ovata either without irrigation or irrigated with meatworks effluent at the same site (Barton, cited in Knight and Nicholas (1996)). The mean annual N accumulation in the current study ranged from 82 to 217 kg N/ha/y, with the current annual N accumulation ranging from 93 to 321 kg N/ha/y (Fig. 4a). These were higher than Ericsson’s (1994) results of 26–130 kg N/ha/y from managed eucalypt stands. For all three species irrigated with effluent, the Mn accumulation at the end of the 3-year period was around twice that in trees without irrigation (Fig. 4f). However, the total Mn input to the site via the effluent irrigation was only 12 kg/ha over the 3 years (4 kg/ha/y). Therefore, effluent irrigation somehow increased tree Mn uptake from the soil reserves rather than from the effluent source. Haynes and Swift (1985) reported that CaCl2 - and HCl-extractable Mn showed broadly similar trends, both increasing markedly as the pH was lowered. As a result, the concentration of Mn and plant biomass in highbush blueberry plants (Vaccinium corymbosum L. cv. Blueray) increased significantly. Therefore, the higher Mn accumulation in the trees irrigated with effluent in the current study could be caused by a reduction of soil pH from 4.8 to 4.0 after the 3-year effluent irrigation (Guo, 1998).
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Nutrient uptake in very young plantations of any species is low because they do not fully occupy the site (Brockway et al., 1982). In the current study, less biomass and nutrient accumulation were found in the first year (Tables 2 and 3, Figs. 2 and 4). Therefore, less effluent should be applied during the first year after the trees have been planted since the nutrient and water consumption is correlated to the growth rate. However, E. globulus stands irrigated with effluent were able to accumulate as much as 104 kg N/ha N in the first year (Fig. 4a). 4.3. Leaf biomass and nutrient accumulation in foliage The major effect of improved nutrient and water availability in the soil is to enhance foliage growth which includes larger leaves as well as more leaves per plant, thereby increasing light interception (Pereira et al., 1989). Usually, the greater the LAI and leaf biomass, the more the total biomass production because leaf is the unit for primary production. In the current study, even though effluent irrigation increased the total aboveground biomass accumulation (Table 2, Fig. 2d), it reduced the leaf proportion of the biomass (Fig. 3a) and tended to reduce LAI (Table 2) but with some exceptions (Fig. 2c). Total net leaf biomass production should include both the leaf biomass on the trees at harvest, and the fallen leaves. More litter fall was found in stands irrigated with effluent, which was consistent across all three species (Guo, 1998). This was possible due to leaf longevity having been reduced when faster tree growth was achieved after effluent was applied. In addition, more branch biomass was found in the stands irrigated with effluent (Fig. 3a), which should support more leaves though some leaves may only live for a short time. Escudero et al. (1992) indicated that the lower the nutrient status of a species the longer the life-span of its leaves. Contrarily, the higher the nutrient status, as in the current study, the shorter the leaf life-span expected. The results from single leaf monitoring indicated that a shorter leaf life occurred on trees irrigated with effluent (Guo, 1998). Therefore, leaf longevity could play a very important role for the trees irrigated with effluent with lower leaf biomass. Manganese toxicity is a major factor limiting plant growth in acidic soils (Foy et al., 1978; Sumner et al., 1991). Leaf shedding results from Mn toxicity for some plant species, e.g. satsuma mandarin (Citrus unshiu Marc.), potato (Solanum tuberosum L.) and cowpea (Vigna unguiculata (L.) Walps.) (Horst, 1988). In the current study, the shorter leaf life and higher litter fall from trees irrigated with effluent could also be caused by more Mn accumulation in the leaf, though light competition after canopy closure may also play some role in it.
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Excess Mn in leaves can cause a decline in photosynthesis in trees (Kitao et al., 1997) and also in other plants, such as tobacco (Nicotiana tabacum L.) (Nable et al., 1988). In the current study however, irrigated eucalypt species grew particularly well, even though the trees had less living leaf than the trees without irrigation. The higher biomass gave no evidence of any photosynthesis decline. Hence, eucalypt species may have relatively high Mn tolerance. Bargali et al. (1992) found foliage was the largest component of nutrient storage although its contribution decreased with age for E. tereticornis plantations at 2–8 years old in Central Himalaya. The relative contribution to the proportion of nutrients in different above-ground components was generally in the order: foliage > bole ðwood þ barkÞ > branch > twig > reproductive parts. Similar results were also found in the current study (Fig. 3), but the leaf contribution decreased only marginally with age during the 3-year period (data not shown). The shorter the rotation, the more the foliage contributes to the total above-ground biomass. Leaves have a short life. Therefore, their harvesting and removal from the site should be a major consideration for crop production and sustainable land use. In effluent land treatment systems, it is necessary to remove foliage frequently for preventing excessive nutrient return from the litter fall. Overall, the design and management of a short rotation forest should be based on its main objective and related to the nutrient cycling within the system. If the short rotation forest is grown solely for energy biomass production, then a species, variety, family or clone with fast growth, high yields and high nutrient use efficiency should be selected. Only the tree parts with high nutrient use efficiency, such as the stemwood, should be removed from the site so that less nutrients will need to be replaced by use of commercial fertilizers. When a short rotation forest is grown to strip nutrients in a land treatment system, the species, variety, family or clone with high growth rates, but with a low nutrient use efficiency should be selected. All above-ground tree parts should be harvested and removed from the site.
5. Conclusions It is important that the correct tree species is selected to achieve maximum biomass production for a given site, and, in the case of a land treatment system, maximise nutrient uptake. Using eucalyptus in a short rotation forest linked with effluent land treatment was a good choice as their growth was not adversely affected by the soil pH reduction which resulted from effluent application. E. globulus showed optimal potential in energy short rotation forests, whether linked with ef-
fluent land treatment or not. To maximize nutrient removal from the site in an effluent land treatment system, the whole of the above-ground biomass should be harvested and removed for energy conversion. Less effluent should be applied in very young plantations.
Acknowledgements The Richmond Meat Processors & Packers Ltd. processing plant at Oringi, and Gary Newnham, a chief engineer, are thanked for their assistance and the permission to undertake the research work on their site.
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