Environmental impact of meat meal fertilizer vs. chemical fertilizer

Environmental impact of meat meal fertilizer vs. chemical fertilizer

Resources, Conservation and Recycling 55 (2011) 1078–1086 Contents lists available at ScienceDirect Resources, Conservation and Recycling journal ho...

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Resources, Conservation and Recycling 55 (2011) 1078–1086

Contents lists available at ScienceDirect

Resources, Conservation and Recycling journal homepage: www.elsevier.com/locate/resconrec

Environmental impact of meat meal fertilizer vs. chemical fertilizer J. Spångberg a,∗ , P.-A. Hansson a , P. Tidåker b , H. Jönsson a a b

Swedish University of Agricultural Sciences, Department of Energy and Technology, Box 7032, 750 07 Uppsala, Sweden Swedish University of Agricultural Sciences, Department of Crop Production Ecology, Box 7043, 750 07 Uppsala, Sweden

a r t i c l e

i n f o

Article history: Received 30 September 2010 Received in revised form 18 April 2011 Accepted 3 June 2011 Keywords: Chemical fertilizer Energy recovery LCA Meat meal Organic fertilizer

a b s t r a c t Animal by-products (ABP) are rich in nutrients and energy. This LCA study assessed and compared the environmental impact of using meat meal as fertilizer with that of using chemical fertilizer. In one system the nutrient content of ABP Category 2 was recovered and used as a meat meal fertilizer on arable land, replacing chemical fertilizers. In the other system a chemical fertilizer was used and the energy content of the ABP material recovered. The functional unit consisted of one kg of harvested spring wheat and treatment of 0.59 kg of ABP Category 2. The system for nutrient recovery and chemical fertilizer replacement had lower emissions of greenhouse gases and acidification than the energy recovery system, but had higher total use of energy and eutrophying emissions. Overall, the results of the study greatly depended on the fuels replaced. © 2011 Elsevier B.V. All rights reserved.

1. Introduction According to the waste hierarchy established by the European Commission, member states are required to promote systems where the waste is re-used, its material recycled or its energy recovered. The treatment with the least negative environmental impact should be used (EC, 2008). Animal by-products (ABP) comprise slaughter waste that is not intended for human consumption. They are divided into three categories according to European regulations. ABP Category 1 is high risk material and has to be incinerated or, rarely, disposed of in an approved landfill. ABP Category 3 present a low risk and can be used for production of pet food. ABP Category 2 includes manure and digestive tract contents, plus animal waste at risk of carrying an infection other than Transmissible Spongiform Encephalopathy (TSE). Both Category 2 and Category 3 materials may be used for production of fertilizer in the form of meat and bone meal, compost or digestate from anaerobic digestion, or may be incinerated (EC, 2002). Use of fertilizers is one of the major environmental issues in agricultural production. Energy used for the production of chemical fertilizers accounts for around 1.2% of total global energy consumption (IFA, 2009). In Swedish agriculture, the production and use of chemical fertilizers account for about 20% of the total energy used (Ahlgren, 2009) and 9% of the greenhouse gas (GHG) emissions (LRF, 2009). The high cadmium content in Swedish agricultural

∗ Corresponding author. Tel.: +46 0 18 671869. E-mail address: [email protected] (J. Spångberg). 0921-3449/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2011.06.002

soils, largely caused by spreading polluted phosphorus fertilizers, is another important environmental aspect, since the cadmium intake with food is close to the recommended tolerable intake (EFSA, 2009). One of the challenges for organic farms without access to manure is to find sustainable sources of plant nutrients, since only natural, renewable and regenerative resources may be used (IFOAM, 2006). Urban organic wastes might represent such a renewable source for both organic and conventional farming. Several ABP fertilizers are allowed in organic production and the N and P use efficiency of meat and bone meal fertilizers has been studied. In addition, field trials on the effects of this type of fertilizer have been conducted in Norway (Jeng et al., 2006) and Sweden (Gruvaeus, 2001, 2002, 2003). The aim of the present study was to assess and compare the environmental impact of two different systems for handling and disposing of ABP Category 2 waste: (i) System MM recovered the nutrient content of ABP by using it as a fertilizer on arable land, replacing chemical fertilizer; while (ii) System CF recovered the energy content of the ABP. In System MM, a meat meal fertilizer (Biofer) made from the ABP material was applied to a spring wheat crop, while animal fat, a by-product from the meat meal production, replaced fuel oil of fossil origin. In System CF, a chemical fertilizer was used to fertilize the spring wheat and the ABP material was combusted in the form of a slurry (Biomal), replacing biofuel. Note that this study did not compare farming systems. Instead, it compared and assessed the environmental impact of plant nutrient recovery from ABP Category 2 with the environmental impact of energy recovery. Location of the farm and slaughterhouse was set to Sweden.

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System MM Agriculture

Animal by-product treatment

Avoided activities

Energy Animal by-products

Resources Chemicals

Agricultural activities

Production meat meal

Production animal fat

Production Biofer 10-3-0

Incineration (1.9 MJ)

1 kg spring wheat

Production fuel oil

Treatment of 0.59 kg ABP category 2

Fig. 1. System boundaries for System MM. Agricultural activities included were ploughing, harrowing twice, combo-drilling, spraying and harvest. The functional unit of the study consisted of 1 kg of spring wheat and the treatment of 0.59 kg of ABP Category 2.

2. Methodology Life Cycle Assessment (LCA) methodology was used, covering all relevant aspects of environmental impact. ISO standards were followed (ISO, 2006a, 2006b). 2.1. Impact categories The impact categories included were: use of total energy and use of renewable energy; greenhouse gas emissions; acidification; eutrophication; main non-renewable resources; and use of land. Energy was included as the total primary energy used and was divided into renewable and non-renewable primary energy carriers. Greenhouse gas emissions were expressed in CO2 -equivalents with the time horizon of 100 years according to Guinée (2002). Acidification was expressed in SO2 -equivalents and eutrophication in O2 -equivalents, both also in accordance with Guinée (2002) and Lindfors et al. (1995). Main non-renewable resources were expressed as a list of all major non-renewable resources that had been used in all phases of the processes included. In addition, the flow of cadmium to the soil was quantified.

the production processes to the use and disposal of by-products and wastes produced. All production sites in the study (production of meat meal, animal fat, Biomal, Biofer, chemical fertilizer and spring wheat) were assumed to be within the Nordic countries. Electricity used at these sites was assumed to be a Nordic average mix, since the electricity market of the Nordic countries is integrated. The farm site was assumed to be located in Vreta, Östergötland, southern Sweden, and the farming system was conventional. 3.1. System MM – meat meal used as fertilizer

System expansion was used in such a way that avoided activities were included in the systems studied (ISO, 2006b; Guinée, 2002). This meant that impacts from avoided activities were subtracted from impacts of included activities, which occasionally led to negative results.

In Sweden there is no processing plant for meat and bone meal. ABP Category 2 waste produced in the south of Sweden was therefore assumed to be sent to Denmark for production of meat and bone meal. The slaughterhouse selected was Team Ugglarp AB in Hörby, which is situated about 70 km from the Danish border. In System MM (Fig. 1), the ABP Category 2 waste was sent from the slaughterhouse to Ortved, Denmark, where a meat meal product was produced (Virta, 2009). At the production site, the ABP was sanitized, animal fat was extracted and the residue dried and milled. The animal fat was assumed to be used directly as fuel in the vicinity of Ortved, often replacing fuel oil (Virta, 2009). Gyllebo Gödning AB in Malmö produces fertilizer products, trade name Biofer, using meat meal from the Ortved plant. The Biofer products are mainly delivered directly to farms when the company has a sufficiently large order to send a full truck to a certain area (Lööf, 2009). In this study, the Biofer was assumed to be taken directly from the production site in Malmö to the farm in Östergötland. At the farm, 80 kg of total nitrogen per hectare were applied to the spring wheat crop. Biofer was spread with a combo seed drill, which is the most common spreading technique in Sweden for this kind of fertilizer. Other field operations included in the study were ploughing, harrowing, application of herbicides and harvest (for further information see Section 4.3.2).

3. System description and system boundaries

3.2. System CF – chemical fertilizer used and ABP incinerated

The study covered environmental impacts from the transport of the ABP from the slaughterhouse via the meat meal production plant to the harvest of the spring wheat. Slaughter was considered the cradle of the ABP Category 2, and thus production of the livestock and the slaughter itself were not included in the study. Products and activities were studied from the raw materials used in

In System CF (Fig. 2) chemical fertilizer (NPK 21-4-7) was used in spring wheat production. The NPK 21-4-7 fertilizer was produced in Uusikaupuuki, Finland, from where it was transported by ship to Åhus in Sweden for packaging (Yara, 2009). From Åhus it was transported to the central supply in Norrköping, and from there the farmer transported it to the farm at Vreta in Östergötland.

2.2. Functional unit The functional unit (FU) of this study consisted of the production of one kg of spring wheat with a dry matter content of 85%, combined with the treatment of 0.59 kg of ABP Category 2. 2.3. System expansion

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System CF Agriculture

Animal by-product treatment

Avoided activities

Energy Animal by-products Resources Chemicals

Production NPK 21-4-7

Production Biomal

Agricultural activities

Incineration (4.5 MJ)

1 kg spring wheat

Production biofuels

Treatment of 0.59 kg ABP Category 2

Fig. 2. System boundaries for System CF. For agricultural activities and functional unit see system boundaries for System MM.

The application rate in the study was 80 kg of total nitrogen per hectare. Spreading and all other field operations were the same as in System MM. In both systems, treatment of 0.59 kg of ABP Category 2 was studied. In System CF, this was done by crushing and grinding the ABP and mixing it with 20 kg of formic acid per 1000 kg of material to form the product Biomal. This process was assumed to take place in Krutmöllan, southern Sweden. From here the Biomal was transported to an industrial park in Perstorp, where it was cocombusted with a base fuel (peat and wood material) in a fluidized bed boiler. Biomal normally replaces some other biofuel or municipal waste. In this study, the Biomal was assumed to replace wood chips produced from a mix of returned chips and forest fuels (Virta, 2009). 3.3. Activities not included Construction of buildings and machinery manufacture were not included for any of the production sites. Similarly, the impact from the production of the ABP was not included, as this was seen as material that would be produced in the same amount and way whatever its future treatment, and thus the burden of this production was allocated to meat production. Both the Biofer and the NPK 21-4-7 fertilizer were packaged in big bags. Only the production of the material for the big bag, and not the sewing or the disposal (mainly recycling) of the bag, was included in this study. Furthermore, use of a few chemicals in minor amounts (less than 1 kg per ton of ABP waste) at the treatment plant at Ortved was neglected. All these activities were assumed to have a negligible impact on the final results. Of the agricultural activities, drying the spring wheat grain was not included, as this was the same for both systems. 4. Data on included main activities 4.1. Treatment and combustion of animal by-products Studies on combustion of Biomal carried out by Scandinavian Energy Project in partnership with Konvex AB have demonstrated that when Biomal is added to combustors, there is no significant increase in emissions (unpublished data). The Swedish Ministry of Agriculture (2001) has also reported that the changes in nitrous oxide (NOx ) and sulphur dioxide (SO2 ) emissions are insignificant when Biomal is incinerated in fluidized bed combustors. In this study it was thus assumed that the use of Biomal did not change

the incinerator emissions at all, even though Svärd et al. (2003) reported that NOx emissions decreased often, but not always, when Biomal replaced up to 35%, by energy, of ordinary fuels. A similar assumption was made for the use of the animal fat replacing fuel oil. This was based on studies showing no change in emissions, except for an occasional tendency for increased NOx emissions that was too inconsistent to be quantified (Wyatt et al., 2005). In this assessment carbon dioxide (CO2 ) emissions of fossil origin were included as a greenhouse gas, while emissions of biogenic origin were not included. 4.2. Data and location for the field studied A farm at Vreta Kloster in Östergötland (58◦ 28.973 N, 15◦ 30.304 E) was used as the location for wheat production and fertilizer use. This was one of the locations of Swedish three-year field trials on the effect of organic fertilizers, including pelletized Biofer 10-3-0, 11-3-0 and 9-4-0, on spring wheat. The crop yield used in this study was the mean yield from these three years of trials (Table 1). The soil is a loam with a relatively high phosphorus and potassium content (Gruvaeus, 2009). 4.3. Transport, field operations and further data sources 4.3.1. Transport steps For the ABP Category 2 material, all transport stages from the slaughterhouse to the farm or the fluidized bed incinerator were included. For chemical fertilizer production, all transport stages from the production site to the farm were included (Table 2). Energy use and emissions were calculated based on data and methods of NTM (2011). 4.3.2. Field operations and fuel consumption Field operations and associated fuel consumption (Table 3) were based on data from the Food and Agriculture Organization of the United Nations (FAO, 1989), which were verified against current practices in the region. Emissions were calculated based on this fuel consumption using emission data from Lindgren et al. (2002). 4.3.3. Further data Primary energy from electricity use was calculated using LCA data covering all steps in the production of the fuel (Uppenberg et al., 2001) and a conversion factor based on production efficiency of the fuel. For nuclear power the factor used was 3.0 (IEA, 2008), for oil 1.8, for natural gas 1.7 and for coal, peat and biofuels 2.3

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Table 1 Results of three-year field trials in central Sweden on the use of Biofera in spring wheat. Year

Amount of total N spread (kg/ha) Number of trials Harvestc Bioferd (kg/ha) -Nitrogen yield (kg/ha) Harvestc NPK 21-4-7 (kg/ha) -Nitrogen yield (kg/ha) a b c d

Value used in studyb

2001

2002

2003

80 5 4390 76 4830 82

80 5 4560 79 4760 85

80 4 4210 76 4730 87

– – 4387 – 4773 –

Data from Gruvaeus (2001, 2002, 2003). Mean value of harvest year 2001–2003. Kernel (pure weight, kg/ha, dry matter content 85%). Biofer 10-3-0 year 2001, Biofer 9-4-0 year 2002 and Biofer 11-3-0 year 2003, all in pelletized form.

Table 2 Transport stages included, distance (km), transported mass (per FU) and means of transport. For all road transports the loading factor was 50% (i.e. the return transport was empty) and 80% for the sea transport. Transport stage

Distance (km)

Transport mass (kg)

Means of transport

ABP Cat. 2 from slaughterhouse to meat meal prod. plant ABP Cat. 2 from slaughterhouse to Biomal prod. plant Meat meal from meat meal prod. plant to Biofer prod. plant Animal fat from meat meal prod. plant to incineration site Meat meal fertilizer from Biofer prod. plant to farm NPK 21-4-7 fertilizer from prod. plant to packaging site NPK 21-4-7 fertilizer from packaging site to central depot NPK 21-4-7 fertilizer central depot to farm Biomal from prod. plant to incineration site

140 30 100 30 420 700 300 50 45

0.59 0.59 0.18 0.07 0.18 0.08 0.08 0.08 0.59

Truck + trailer (max 22 t) Truck + trailer (max 22 t) Truck + trailer (max 22 t) Truck + trailer (max 22 t) Heavy truck (max 15 t) Container shipa Heavy truck (max 15 t) Small truck (max 5 t) Truck + trailer (max 22 t)

a

1400 TEU (TEU = twenty-foot equivalent unit).

(Uppenberg et al., 2001). For wind and hydro power the factor used was 1.0 (IEA, 2008). Further data sources used on production processes, cadmium content of fertilizers, emissions to air and water from soil, fuels and electricity are given in Table 4. 5. Results

5.2. Emissions

5.1. Energy use System MM was a net user of total primary energy, but the animal fat by-product also replaced the use of non-renewable primary energy in the form of fuel oil (Fig. 3). System CF, on the other hand, delivered primary energy, due to utilizing the high energy content of the raw ABP Category 2 material efficiently in the form of the biofuel Biomal, which replaced other non-renewable primary energy. For System MM the main use of energy was for the production of meat meal, and the animal fat by-product almost replaced enough fossil oil to compensate for the energy use of all the other processes in the system (Fig. 3). For System CF, the Biomal replaced sufficient amounts of other biofuels for the system to give a net delivery of primary energy. Of the total primary energy use, energy that derived

Table 3 Field operations, number of passes and fuel consumption. Field operationa

Passes

Fuel consumption (l/ha)b

Ploughing Harrowing Combo-drilling Field spraying Harvest including transportd

1 2 1 1 1

20.2 3.8 and 3.1c 3.7 0.5 20.0

a

from non-renewable sources was −0.13 MJ per FU for System MM and 2.06 MJ per FU for System CF. In System CF, the N production represented 98% of the energy used in fertilizer production and around 24% of the total primary energy use by the system (primary energy for substituted biofuels excluded).

FAO (1989), supplemented by advice from Rydberg (2010) that ploughing plus harrowing twice is typical nowadays for this area and type of farm. b FAO (1989). c Fuel consumption for harrowing in the first and the second pass, respectively. d Transport included was 1 km from field to farm (FAO, 1989).

5.2.1. Greenhouse gases The most important factor affecting the emissions of the greenhouse gases included in the study (CO2 , CH4 and N2 O) was the avoided emissions due to replacing fuel oil with animal fat in System MM, which outweighed the emissions from the production of Table 4 Further data sources used in the study. Process/parameter

Reference

Pelletizing process Production NPK 21-4-7 -Global warming potential, GWP -Energy use

Green (2009)

-Other emissions LCA data for big bag material Generic emission equivalents Soil N2 O emissions Leakage of N and P from soil

Cadmium content of NPK 21-4-7 Cadmium content of Biofer LCA data for fuels Electricity – Nordic average mix and grid losses (7%)

Yara (2010) Jenssen and Kongshaug (2003) (with data for modern technology) Davis and Haglund (1999) EuroPlastics (2009) Kärrman and Jönsson (2001), Guinée (2002) IPCC (2006) (using default values for Tier 1 equation) Stjernman Forsberg et al. (2009) (using values for area E23) Yara (2009) Swedish Board of Agriculture (2009) Uppenberg et al. (2001) Nordel (2008)

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Fig. 3. Use of primary energy, MJ per FU, divided between different activities in Systems MM and CF.

the meat meal and animal fat, but not from the remaining parts of the system (Fig. 4). In total, System CF had about three times higher emissions of greenhouse gases than System MM. 5.2.2. Potential acidification The potentially acidifying emissions of SO2 , HCl, HF, NOx and NH3 were included in the study. In total, the potentially acidifying emissions from both systems were similar, 0.70 g SO2 -equivalents

per FU for System MM and 0.71 g SO2 -equivalents for System CF (Fig. 5). In System CF, production of NPK 21-4-7 gave a relatively high contribution to the acidification impact, but was largely counter-balanced by a low acidification impact from the ABP Category 2 treatment and the avoided acidifying emissions due to the avoided biofuels of forestry origin. The total potentially acidifying emissions due to ABP Category 2 treatment and fertilizer production in System CF were 70% higher than the corresponding total for

Fig. 4. Greenhouse gas emissions, g CO2 -equivalents per FU, for Systems MM and CF.

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Fig. 5. Potentially acidifying emissions, g SO2 -equivalents per FU, for Systems MM and CF.

System MM, but the avoided acidifying emissions were also higher for System CF. This meant that while the total potentially acidifying emissions were about the same, their main location changed.

5.2.3. Potential eutrophication Eutrophying emissions included in the study were PO4 3− , H3 PO4 , P, NOx , NO2 , NH3 , NH4 + , NO3 − , HNO3 , N and COD and eutrophication was evaluated for water (Fig. 6). For both systems, the leakage of N and P from soil totally dominated potential eutrophication, with a contribution of 94% to the category “soil and field operations”, and 95% and 98% to the total potentially eutrophying contributions of the System MM and System CF, respectively. The soil emissions per hectare were assumed to be the same for both systems and this meant that also the total eutrophying emissions per hectare were also almost the same for the two systems. Per FU however, the potentially eutrophying emissions were larger for System MM as the field area per FU was 2.25 m2 for this system compared with 2.10 m2 for System CF. As in previous sections, negative values were due to avoided use of fuel.

5.3. Use of non-renewable resources System CF used more of all non-renewable energy carriers studied. It also used much more dolomite, phosphorus and sulphur, due to the production of NPK 21-4-7 fertilizer. The animal fat replacing fuel oil in System MM led to avoided use of oil, and thus much less fossil oil was used in System MM than in System CF (Table 5).

5.4. Land use The lower yield of spring wheat in System MM led to this system requiring acreage of 2.25 m2 per FU, while System CF required 2.10 m2 per FU.

5.5. Cadmium added to soil System MM added a slightly larger amount of cadmium to the arable soil than System CF. Cadmium is a naturally occurring impurity in most phosphorus sources, and occurs both in NPK 21-4-7 fertilizer and in Biofer. Biofer contains less cadmium per kg of phosphorus than NPK 21-4-7, but as Biofer added much more phosphorus per FU, in total a slightly larger amount of cadmium was added to the soil for System MM (16 ␮g per FU) than for System CF (14 ␮g). 5.6. Sensitivity analyses 5.6.1. Use of NPK 21-4-0 instead of NPK 21-4-7 Biofer does not contain any potassium while NPK 21-4-7 contains 7% of potassium. It is therefore interesting to investigate the impact of the potassium included in NPK 21-4-7. Calculations based on Jenssen and Kongshaug (2003) showed that the use of energy and the emissions of greenhouse gases would have been

Table 5 Non-renewable resources (>0.1 g per FU) used by the systems (g). Resource Energy carriers Fossil oil Natural gas Coal Peat Uranium Other resources Dolomite Sulphur Phosphorus Iron Copper

System MM −32 16 2 0.02 0.09 0.02 0.001 0 0.04 0.3

System CF 17 22 6 1.3 0.12 9.10 9.547 3.0 0.02 0.2

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Fig. 6. Potentially eutrophying emissions, g O2 -equivalents per FU, for Systems MM and CF.

about 2% lower for NPK 21-4-0 than for NPK 21-4-7. The same would be true per FU provided that the yield did not change, which is a good assumption for this combination of soil and crop. 5.6.2. Biomal replacing coal instead of biofuels Year 2008, coal consumption represented 30% of the fuels used in conventional thermal power plants within the EU countries (Eurostat, 2010). If Biomal, in a European scenario, had replaced coal instead of biofuels, GHG emissions would have decreased from 162 to 55 g CO2 -equivalents per FU for System CF. Eutrophication and acidification impact would both have increased (by 2 and 6%, respectively), but eutrophication impact would still have been lower for System CF than for System MM. Acidification impact would have remained larger for System CF than for System MM. Total use of primary energy of non-renewable origin would have decreased by 5.3 MJ per FU for System CF, resulting in a use of −3.2 MJ per FU compared with −0.1 MJ per FU in System MM. 5.6.3. Average European 2003 data for chemical fertilizer production In this study, the data for energy use in NPK production were for modern technology (Jenssen and Kongshaug, 2003) while site-specific data (Yara, 2010) were used for the greenhouse gas emissions. In Europe, there are still many production sites producing chemical fertilizers using old technology. When average, instead of modern, European production data (Jenssen and Kongshaug, 2003) were used, the energy use for System CF increased by about 9%, with a value for the system total of −2.0 instead of −2.2 MJ per FU. GHG emissions for System CF increased by 44%, making it 4.6 times that of System MM.

6. Discussion 6.1. Replaced fuels The type of fuel replaced by the animal fat and the Biomal had a major impact on the results, which agrees well with findings by Finnveden et al. (2000) in a study on solid waste treatment. If and when the use of fuel oil of non-renewable origin is phased out, the results will change significantly. In Europe, incineration of ABP is a common disposal route in most Member States (EC, 2001). A sensitivity analysis in the present study demonstrated that if the Biomal in System CF replaced coal, a fuel of non-renewable origin, System CF would give lower GHG emissions than System MM instead of the other way around (see Section 5.6.2).

6.2. Plant nutrients and non-renewable resources Production of chemical NPK 21-4-7 fertilizer uses large amounts of non-renewable resources such as phosphorus, sulphur and dolomite. Phosphorus and sulphur are non-renewable resources with economic reserves estimated to last 23–100 years at the present level of use and with present technology (USGS, 2002; Cordell, 2010). Nitrogen is not a non-renewable resource, but the production of plant-available N is energy demanding and depends on non-renewable energy resources. This large use of non-renewable energy resources, as well as the large use of other non-renewable resources, e.g. coal, raw phosphorus, dolomite, sulphur etc., by System CF is not sustainable, especially since the demand for food is steadily increasing in the world. The need for non-renewable resources can be decreased by recycling wastes rich in plant nutrients as a fertilizer, as demonstrated by System MM,

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and by using renewable energy for producing chemical nitrogen fertilizer (Ahlgren, 2009).

6.3. Differences in fertilizer composition Biofer added significantly higher amounts of phosphorus per hectare than the chemical fertilizer (24 kg of P/ha added with Biofer 10-3-0 compared with 15 kg/ha of P added with NPK 21-4-7). Due to the high phosphorus content of the soil (Table 1), this was estimated not to affect the yield but should still be taken into consideration, as it means that System MM increased soil stores of phosphorus, which can be used by subsequent crops. Potassium was added with the chemical fertilizer, but not with the Biofer. Natural mineralization of potassium in the soil at Vreta (see Section 4.2) should suffice for cereal crops and it is thus not expected that the amount of potassium added had any effect on the yield of spring wheat (Gruvaeus, 2009). Biofer 10-3-0 contains organic carbon and micronutrients such as manganese, iron, copper, nickel and zinc, whereas the NPK 214-7 fertilizer does not. Other comparable meat and bone meal fertilizers have a carbon content of around 30% (Jeng et al., 2006). Assuming this also for Biofer, it would imply that about 50 grams of organic carbon were added per FU, or about 200 kg per ha. This can be compared with the amount of organic carbon in the crop residues (roots and straw), which for the wheat in System MM and System CF can be estimated at 4220 and 4520 kg/ha, respectively (Bolinder et al., 2007). Thus, the meat meal fertilizer might increase the flow of organic C to the soil by about 5% or, if the straw is removed, by 16%. Most chemical phosphorus fertilizers sold in Sweden contain about 4.5 mg Cd per kg P, while Biofer 10-3-0 contains about 3 mg Cd per kg P. This is an important aspect, since the European Food Safety Agency (EFSA) (2009) assessed the mean European intake of cadmium to be 2.3 ␮g/kg b.w. per week, while the tolerable level is estimated at 2.5 ␮g/kg b.w. per week. About half of the cadmium intake comes from food and originates from agricultural soil, the content of which depends on geological parent material, chemical fertilizers used and atmospheric deposition (Eriksson, 2009). The total amount of cadmium added to the soil in the two systems studied here ended up being fairly similar, due to the larger addition of phosphorus in System MM (see Section 5.5).

6.4. Mineralization of nitrogen and phosphorus The relative P use efficiency of meat and bone meal relative to P in chemical fertilizer is around 50% in the first crop, with residual effects in the following year (Jeng et al., 2006). In this study the N use efficiency of Biofer relative to chemical fertilizers was about 90% (Gruvaeus, 2001, 2002, 2003). These facts indicate that the risk of increased nitrogen leaching was low, but due to the higher application of phosphorus when meat meal was added, the risk of emissions of particulate phosphorus, through runoff and internal erosion, might be somewhat increased. This could be decreased by lower addition of phosphorus in the following year.

6.5. Relevance for organic and conventional agriculture Meat meal fertilizers are interesting sources of nutrients, especially in organic agriculture where farms without access to manure are short of alternative P sources. In conventional farming, these fertilizers can contribute to decreasing the GHG emissions compared with using chemical fertilizers, as shown in this study, and thus give lower impact agricultural systems.

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7. Conclusions Using meat meal from ABP Category 2 as fertilizer in Sweden, to replace chemical nitrogen fertilizer, decreased greenhouse gas emissions and use of non-renewable energy, but increased the use of total energy. Acidifying emissions were slightly decreased, while potentially eutrophying emissions to water were increased. The use of many non-renewable resources decreased, while the flow of cadmium to soil stayed approximately the same. Whether it is better to recover the plant nutrients or the energy in ABP Category 2 materials depends on the infrastructure and the environmental priorities of society.

Acknowledgements The financial support provided by the Swedish Research Council Formas for this study is gratefully acknowledged.

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