Org. Agr. (2011) 1:55–64 DOI 10.1007/s13165-011-0005-4
Modelling sustainability: what are the factors that influence sustainability of organic fruit production systems in New Zealand? Girija Page
Received: 11 January 2010 / Accepted: 27 January 2011 / Published online: 14 February 2011 # Springer Science & Business Media BV 2011
Abstract Although many believe that organic systems are sustainable as compared to conventional systems, there is a need to study the sustainability of organic systems per se. In this paper, sustainability of organic kiwifruit and apple production systems is modelled based on the concept of strong sustainability which gives utmost importance to environmental sustainability. Sustainability assessment is undertaken through analyses of key energy and material flows of the orchard system and their impacts on the environment. The proposed approach is based on two high level criteria for sustainability: energy efficiency and non-degradation of the environment. Five indicators which address the two criteria for sustainability are the energy ratio, carbon ratio, change in soil carbon level, soil nutrient balances and leaching of nitrogen. Sustainability indicators are estimated over one production year using two computer modelling tools, Overseer® and Stella®. Sustainability assessment indicates that the organic kiwifruit and apple systems are efficient in energy use and are a net carbon sink over a typical production year. The apple systems mined potassium from the soil which may be a threat to future yield and sustainability. Transition to sustainable farming systems implies reliance to a G. Page (*) School of Natural Sciences M15, University of Western Sydney, Locked Bag 1797, Penrith South DC 1797, NSW, Australia e-mail:
[email protected]
lesser extent on non-renewable energies and recognising the environmental bottom line. Keywords Energy and material flows . Organic orchard systems . Energy efficiency . Environmental impacts
Introduction The sustainability of agricultural systems has been a focus of much debate in research and policy since the 1970s. Even so, assessment of agricultural sustainability remains an elusive concept in both arenas. Although sustainability discussions initially began with a strong emphasis on environmental protection, in recent times the concept grew to include socioeconomic concerns as well. As such sustainability is perceived from predominantly economic, environmental and social point of view (Douglass 1984; Pannell and Schilizzi 1999). Although economic and social considerations are important, sustainability essentially has an environmental bottom line (Daly 1991; Goodland and Daly 1996). Such a concept is captured by strong sustainability. In strong sustainability, the utmost priority is accorded to the maintenance of healthy environmental conditions (Neumayer 2004). Environmental sustainability is considered nonnegotiable because the sustainability of any human economic system is ultimately constrained by the finite capacity of the environment to provide resources and
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act as a sink for wastes (Adams 2006; Daly 1991; Douglass 1984; Goodland and Daly 1996). Additionally, the environment also provides basic life support system on the Earth which cannot be replaced by human endeavour (Ekins et al. 2003). Although organic farming systems are thought to tread gentler on the environment than the conventional systems, organic farming does not mean zero environmental impacts (Mouron et al. 2006; Rigby and Caceres 2000). Organic kiwifruit and apples in New Zealand are coming under increasing pressure to grow quality fruit with minimum environmental damage if New Zealand is to continue exporting to the Northern Hemisphere. There is a need to model sustainability of these organic orchard systems per se. The purpose in this paper is to develop and apply an assessment model based on strong sustainability in order to identify the factors that influence sustainability of organic kiwifruit and apple production systems in New Zealand.
The conceptual model for sustainability This research is motivated by the premise that if agricultural practices degrade the environment, they cannot be sustainable. The orchard system interacts with the natural environment in which it is embedded, through energy and material flows (Fig. 1). Management decisions are important in deciding the magnitude and type of energy and material flows on the orchard, which may have varying degrees of impacts on the environment (Ruth 1993). The energy and material flows are constrained by the laws of
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thermodynamics (Ruth 1993). Energy flows, especially those derived from non-renewable resources, have links with material flows and they are associated with negative environmental impacts, such as the release of greenhouse gases (Svensson et al. 2006). Material flows also affect the energy flows, since the use of inputs such as fertilisers or machinery or any other production input has energy embodied in them (since matter contains energy according to Einstein’s famous equation E=mc2). Thus, the magnitude of energy used by the system changes as new matter is brought into the system with subsequent impacts on the environment (Ruth 1993). Sustainability assessment is undertaken through the analysis of key energy and material flows within the orchard and between the orchard system and the environment. The orchard system consists of the fruit trees, soil system and the atmosphere (Fig. 2). The fruit trees transform the energy–matter inputs into fruit energy output. Simultaneous material flows of CO2-equivalent emissions occur to the atmosphere, when energy inputs are used. Inputs such as fertilisers, affect soil quality and water quality. A part of the CO2-equivalent emissions is offset in plant biomass through photosynthesis. A portion of organic matter that enters the orchard soil stays there, whilst the rest is emitted to the atmosphere as CO2equivalent emissions. All these interactions need to be considered in assessing sustainability using life cycle thinking. As the environment has a limited capacity to provide resources and assimilate impacts, management practices should be based on the reduction in anthropogenic material and energy flows, especially
Fig. 1 Orchard system and the natural environment (adapted from Ruth 1993)
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Fig. 2 An orchard system for sustainability assessment CO2 equiv. emissions
Atmosphere
Energy and material inputs:
Soil
Machinery Equipment Diesel Irrigation system Fertilisers Transport Agrichemicals Tree support system
Fruit trees Fruit energy
Leaching
derived from non-renewable sources, in order to achieve sustainability (Hinterberger et al. 1997; Neumayer 2004). However, absolute preservation of non-renewable resources is not realistic and needs to be replaced by acceptable levels of compromise (Raman 2006; Turner et al. 1994). This is because firstly, human economic systems are very much dependent on primary resources and secondly, humans are a part of nature and therefore they interact with nature through energy and material flows. Also, non-renewable resources (fossil fuels and minerals) are used in less proportions by life forms other than humans and so extracting them can be considered irrelevant to the biosphere, insofar as the environment is not degraded (Haberl et al. 2004). Thus, sustainability at the orchard system level is based on two criteria: efficient use of energy and non-degradation of the environment (Page 2009).
Fruit
Energy efficiency Energy ratio is used as an indicator to estimate efficiency of energy input to fruit energy output. Energy output is the energy in fruit that is physiologically available1 for humans and energy input is the direct and embodied energy, both expressed in thermal equivalents. The direct energy and the embodied energy take into consideration the following: Direct energy—energy used in fuels, lubricants and human labour for carrying out various operations. Embodied energy—energy used in manufacture, packaging and delivery of all inputs such as agrichemicals, machinery and fertilisers to and within New Zealand. The energy output/input ratio should be one or more in order for the orchard production system to be energy efficient (Fakhrul Islam et al. 2003; Reganold et al. 2001; Schlosser et al. 2003).
Methodology Non-degradation of the environment The two high level criteria for sustainability namely energy efficiency and non-degradation of the environment need to be more specifically defined for application at the orchard systems level. Five indicators which are based on the two high level criteria are used in this study: energy efficiency, carbon ratio, change in soil carbon level, soil nutrient balances and leaching.
Organic fruit production systems interact with and impact on the environment in various ways. They use 1 Physiologically available energy is the energy obtained by subtracting energy lost in the excreta from the total energy value of the food.
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non-renewable resources; they affect soil, atmosphere and water quality and they have an impact on biodiversity. As long as these impacts are assimilated by the biophysical limits of the environment, the orchard system will function like a natural ecosystem with minimal environmental degradation (Adams 2006; Kim 2004). Hence, the environmental impacts arising from the energy and matter use by an orchard system have to be within the appropriate ranges of tolerability (Eckert et al. 2000). Towards this end, four key indicators along with the threshold values are described.
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of carbon dioxide and nitrous oxide (which is expressed in CO2 equivalents) (Paustian et al. 2000). In order for an orchard system to be sustainable, the change over time in soil carbon levels should be nonnegative. This means that the carbon input should be at least as great as the carbon loss in the soil indicating soil carbon sequestration. Soil carbon level is an important indicator of soil organic matter, which in turn is an indicator of soil quality. Hence, change in soil carbon level is considered here as a separate indicator, even though the carbon sequestered in and lost from the orchard soil is accounted for in the carbon ratio calculations.
Carbon ratio Soil nutrient balances The carbon ratio considers the impacts on the atmosphere in terms of greenhouse gas emissions. It is the ratio of carbon sequestered to carbon emitted, expressed in CO2-equivalent units. In the orchard system, carbon is sequestered in the vines/trees through the process of photosynthesis and also is temporarily stored in the compost (Kroodsma and Field 2006; Shepherd et al. 2003). Carbon emissions occur during manufacturing, distributing, and the use of management inputs (direct and embodied energy), as well as from decomposition of mulched prunings, leaves, fine roots, compost and other organic material already present in the soil (Di and Cameron 2002; Grogan and Matthews 2002; Mouron et al. 2006). Nitrous oxide from the orchard soil (expressed in CO2 equivalents) also adds to the carbon emissions from the orchard system. The carbon ratio has to be one (the system is carbon neutral) or higher than one (the system is net carbon sink) so that the environment is not degraded and the system is sustainable. Change in soil carbon level Change in soil carbon level is estimated as a balance between carbon input and carbon loss in the orchard soil. Sequestration of carbon in the soil enhances soil quality and occurs when carbon input exceeds carbon loss (Audsley 1997; Johnston 1986). Carbon input to the orchard soil is through the addition of organic matter from prunings (leaves and stems), fine roots and compost (when applied). However, not all the carbon that enters the orchard soil through organic matter stays in the soil. Carbon loss occurs through microbial decomposition of organic matter in the form
Nutrient balances are important indicators of soil quality. For each nutrient, the balance is estimated between the input of nutrients from fertilisers, soil mineralisation, rainfall, and cover crops and the output or withdrawal of nutrients from the soil in fruit, plant, leaching and gaseous losses (Di and Cameron 2002). When nutrient inputs are in balance with nutrient outputs, the crop requirements are met, and losses to the environment are minimised. A negative nutrient balance (nutrient deficit) indicates that the system relies on mining soil nutrient reserves for production and is not sustainable. A positive nutrient balance (nutrient surplus) is generally considered sustainable, especially because poor soil fertility is a constraint to future crop production (Harris 1998). However, a large surplus of a particular nutrient increases the chances of it being lost to the environment, possibly with negative consequences. In this research, a sustainable nutrient balance is nonnegative; unsustainable, large positive nutrient balances (nitrogen in this case) are accounted for in the nitrogen (N)-leaching indicator. Leaching of N Leaching of N from a farming system is an important indicator of the potential threat of eutrophication of waterways (Di and Cameron 2002) as well as a potential threat to human health. While the World Health Organisation’s threshold level for human health is no greater than 11 mg N/L, the exact level of N-leaching that constitutes a threat of eutrophication depends on the particular ecosystem. The
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reference value for N concentrations which might cause eutrophication in New Zealand aquatic ecosystems was not known. In the absence of this reference value, an orchard system was considered to pose a potential threat of eutrophication if the leaching level of N from the orchard system is higher than 0.5 mg N/L2 (Pierzynski et al. 2005). Data collection and computer modelling Two types of data were required to model sustainability of organic orchard systems: primary and secondary. Primary data were gathered from a number of commercial organic kiwifruit and apple orchardists. The orchards had mature crops that were in full production. Primary data included the energy and matter inputs that were brought in by the orchard manager in order to carry out various production practices for a typical production year. The key variation in the intensity of management inputs was addressed by undertaking scenario analysis. Primary data on orchard production practices were gathered through semi-structured interviews with either the growers or the orchard managers. These included the calendar of key operations and the various inputs used in carrying out those operations. The secondary sources of data were the energy–matter coefficients taken from the published literature. These coefficients were used to convert primary data into appropriate energy–matter equivalents and are described elsewhere (Page 2009). The selected orchards ranged from relatively small to relatively large operations. After interviewing five organic kiwifruit orchardists, it was concluded that the key annual production practices and the range of inputs used on a per hectare basis across the orchards were more or less similar, so therefore no further orchardists were interviewed. After interviewing five apple orchardists, it was observed that there are inherent differences between the types of manage2
This may seem overly restrictive, since concentration in leachate does not necessarily translate to similar concentrations in the receiving water-body. It is acknowledged that N concentration in water-bodies depends on several factors such as cumulative effects of nutrient leaching, the number of orchards in the area and the geographical characteristics of the catchment; however, the actual threshold level may be adjusted without affecting the usefulness of the indicator. This does serve to highlight the need for more research on this topic.
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ment inputs used across the orchards, which gave a wide variation in yields. To address these variations, it was decided to develop two separate model apple systems for sustainability analyses. The first system represents the orchards which are semi-intensive, with lower yields and to which relatively lower number of sprays are applied, whilst the other system represents orchards which are intensive, with higher yields and uses a higher number of sprays. A model organic kiwifruit system and apple system, typical of the orchards studied was derived respectively, and sustainability assessment was undertaken for this model system. The key description of the model systems is presented in Tables 1 and 2. It must be noted that it was not the purpose of this research to generalise beyond the studied orchards, in order to answer the question of whether the organic kiwifruit and organic apple systems in New Zealand are sustainable. The purpose, instead, was to apply the proposed assessment to the model systems, in order to identify key factors that influence their sustainability. Two computer modelling software tools (Stella® version 9.0.1 and Overseer® nutrient budget 2, version 5.2.4.0) were used to estimate five sustainability indicators. The same tools were used to identify the effect of key scenarios in management on the values of sustainability indicators. Stella® which is systems dynamic software was used to estimate three sustainability indicators: the energy ratio, the carbon ratio and the changes in soil carbon level. Overseer® nutrient budget programme which is commonly used in New Zealand enabled the estimation of two sustainability indicators: nutrient balances and leaching of N. Overseer® also estimated nitrous oxide (N2O) emissions from the orchard soil which became an input to the total carbon equivalent emissions in the Stella® model. The boundary for modelling sustainability of each orchard system ended when the fruit reached the pack house gate. Embodied energy was included one step backwards as the energy used in manufacturing, packaging and transporting inputs such as machinery and fertilisers to and within New Zealand.
Results The results (Table 3) indicate that the model systems are efficient in the conversion of energy in inputs to
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Table 1 Key description of the model organic orchard systems over a typical year Kiwifruit (500 vines per hectare)
Semi-intensive apple (800 trees per hectare)
Intensive apple (1,250 tress per hectare)
Area (ha)
5
10
65
Tractor power (kW)
45
50
50
Soil type
Volcanic loams
Alluvial loams
Alluvial loams
Irrigation
No
Yes
Yes
Yield (t/ha)
21
37
54
Compost application
8 t/ha/yr
Once in 4 years
Once in 4 years
No. of sprays
7
29
36
Aerial spray
No
No
Yes
Frost protection
No
No
No
Table 2 Specific management inputs of the model organic orchard systems over a typical year Item
Kiwifruit (800 vines per hectare)
Semi-intensive apple (800 trees per hectare)
Intensive apple (1,250 trees per hectare)
Spraying programme per hectare Fish oil (L)
60
NA
Compost tea (L)
200
100
NA NA
Seaweed (L)
30
NA
NA
Bacillus thuringiensis (kg)
1.06
NA
0.3
Mineral oil (L)
30
30
40
Organic bud enhancers (L)
65
NA
NA
Lime sulphur (kg)
NA
127
406
Copper fungicides (kg)
NA
5.2
7.4
Sulphur fungicides (kg)
NA
12
4
Codling moth granulosis virus (g)
NA
660
22
Spinosad (g)
NA
480
240
Liquid magnesium sulphate (kg)
NA
1
NA
Molasses (L)
NA
NA
15
Biomin calcium (L)
NA
NA
1
Fertilisers per hectare (kg) Ag lime
500
300
300
Blood and bone
NA
NA
500
Rock phosphate
250
NA
100
Kieserite
200
NA
300
Biophos
NA
500
NA
Potassium sulphate
200
NA
NA
Spraying
50
189
275
Mowing
43
47
42
Mulching
43
21
26
Forklift
6
8
10
Diesel consumption per hectare (L)
NA not applied
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Table 3 Results from sustainability assessment of the model organic orchard systems over a typical year Kiwifruit system (500 trees per hectare)
Semi-intensive apple (800 trees per hectare)
Intensive apple (1,250 trees per hectare)
Energy ratio
1.57
1.57
1.84
Carbon ratio
1.13
1.24
1.23
a
846
878
980
Soil nutrient balance
No deficiency
K deficiency
K deficiency
N leaching (mg N/L)
1
14
5
Change in soil C level (kg/ha)
C carbon, K potassium a
Soil carbon sequestration
fruit energy in output and therefore meet the first criterion for sustainability as proposed in this paper. The second criterion for sustainability—the nondegradation of the environment—is met partially. The carbon ratio indicates that the model systems offset the carbon equivalent emissions and therefore they are net sinks of these emissions. The output of potassium is higher than the input of potassium and potassium requirement is met by depleting soil potassium reserves in apple systems. The model systems leached N at levels that can potentially cause eutrophication as per the threshold level considered in this research.
Discussion As the threshold level for each indicator is defined, the results from the model can guide in making informed decisions in management practices to enhance sustainability. Three key areas in management to improve sustainability are discussed. First, it was identified that nutrient management on apple orchards is an area of concern. The sustainability assessment indicated that both apple systems relied on soil potassium reserves to satisfy their potassium requirements. Organic orchard systems are usually faced with the challenge of supplying adequate amounts of nutrients to satisfy the crop requirements within the range of fertilisers permitted under organic certification schemes (Canals 2003). Hence, annual application of composts, application of potassium sulphate, and increased use of biophos may alleviate potassium deficiencies in the orchard soil. However, these may have an effect on leaching losses and total energy use. Due to these trade-offs, it is not always possible to recommend concrete areas in
management practices to improve the sustainability of organic orchard systems. Second, the use of smaller tractors can reduce energy consumed in spraying operation. Spraying was the most energy intensive management practice in the three model systems, which was carried out with the help of a sprayer attached to the tractor. The apple growers usually preferred bigger tractors because they are economical (Table 1). Using bigger tractors means greater embodied energy content and higher fuel consumption. This research suggested that the energy saving of up to 2 GJ per hectare per year can be achieved in apple orchards by using a smaller powered tractor (from 50 to 40 kW) even though it took 10% more time to undertake the spraying operation. Simultaneously, there were reductions in associated carbon emissions which increased the carbon ratio. Another logical way to reduce energy use and associated carbon emission in spraying operation is the reduction in the frequency of sprays. However, this scenario was not considered given the fact that the frequency of sprays is usually dictated by weather. Third, site selection for orchard establishment is an important factor for enhancing sustainability. Orchard location can influence sustainability through the requirement of energy consuming inputs such as irrigation and frost protection (wind machines). Irrigation is not normally required for the commercial growing of organic kiwifruit in New Zealand. However, orchards located on the light, free draining pumice soil in the Eastern Bay of Plenty, which are prone to drought, especially during spring and summer, require irrigation. Similarly, the requirement of frost protection system depends on the orchard location. The management scenario analysis sug-
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gested that the irrigation system in kiwifruits and frost protection system in kiwifruits and apples are the most energy intensive inputs when used. Hence, selecting an appropriate site during the establishment phase of the orchard is important in the overall aim to achieve environmental sustainability by reducing non-renewable energy use and associated carbon emissions. Although, the energy ratio (Table 3) provides insights into the efficiency of energy conversion at the orchard systems level, it has to be interpreted with caution. There are two reasons for this. First, the energy ratio only indicates the output of useful food energy per megajoule of energy invested. In reality, the various energy inputs used in orchard production processes are less than perfectly substitutable with each other or with the food energy in fruit (a megajoule of fossil fuel is qualitatively different from a megajoule of fruit energy) (Cutler 2007). Second, dependence on non-renewable energy is, by definition, unsustainable; obviously as a long as any system depends on non-renewable resources, it will not be sustainable (Edwards-Jones and Howells 2001). Limitations in the quantitative approach taken meant that some issues were not considered in the proposed sustainability assessment. First, the use of copper in organic orchard systems is an issue that is important in the discussion of impacts on soil biodiversity. Although none of the growers exceeded the BioGro limit of annual copper application of 3 kg/ha/year (BioGro 2004), it can be expected that year-afteryear sprays of copper might lead to copper build-up in soil which can affect soil biodiversity adversely (Morgan and Taylor 2003). Also, organic orchard production negatively affects biodiversity in general through clearing of the land for orchard establishment (Gudmundsson and Hojer 1996). At the same time, organic growing may have beneficial effects on aboveground biodiversity than their conventional counterparts (Hole et al. 2005). However, these relationships could not be captured in the present framework because of lack of data. Second, sustainability indicators were estimated for a typical production year without considering year to year variability. Ideally, sustainability assessment should consider the entire life cycle of an orchard system from establishment through to the fate of the orchard crops at the end of life cycle (replaced after every 40–50 years). As more data
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become available, it would be possible to estimate the value of sustainability indicators over the life cycle of an orchard system. Sustainability based on the theory of strong sustainability gives primary importance to environmental sustainability, followed by socio-economic concerns (Daly 1991). This research suggests that model organic orchard systems in this study are sustainable environmentally in many respects. However, many argue that organic systems may be less sustainable economically since their yields are often lower than yields in the conventional systems (Blaschke et al. 1991; Daly 1994; Stokstad 2002; Yunlong and Smit 1994). They suggest that the definition of sustainability should consider the three components of sustainability: economic, social and environmental, simultaneously (Gomez et al. 1996; Rasul and Thapa 2004; Smyth and Dumanski 1993). Although social and economic considerations are important, sustainability essentially has an environmental bottom line. This implies, once the two environmental criteria as proposed in this research are met, other indicators that are consistent with socio-economic criteria for sustainability can be considered within the present framework.
Conclusions The proposed model for assessing sustainability is a step forward to identifying when the biophysical limits are approached as a result of key energy and material flows of the organic orchard management practices. Some specific areas in management to move towards sustainability of the studied systems imply that there is a need to change the grower behaviour which currently appears to exploit the natural capital by depleting the soil potassium reserves in organic apple systems and the fact that the growers usually prefer bigger tractors which consume more non-renewable resources. Considering year to year variability will give a more accurate picture of the values of sustainability indicators over any single year. Although the studied orchard systems passed the sustainability criteria for energy efficiency in this research, it has to be interpreted with caution. Since fossil fuels will be exhausted in some future point in time, the challenge remains for research to develop food production systems with higher yields that rely to a lesser extent on non-renewable energies. This means
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identification of strategies that will systematically reduce the dependence on non-renewable resources in order to progress towards the path to sustainability. Acknowledgements The support of participating orchardists, Massey University Doctoral Scholarship and Cecil Elliot Trust Grant is acknowledged.
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