1 Introduction
Demand for apatite mining for phosphorus (P) and for conversion of nitrogen (N) into its reactive form for use in fertilisers has increased the use of P and N. Even though nutrient balances and emissions of N and P have been monitored extensively, particularly in farming, an indication of nutrient use efficiency (NutUE) through the entire food chain has been lacking.
In this study, our aim was to develop further the basic nutrient footprint method introduced recently by Grönman et al. (
2016) by applying it to an animal food product—beef. The nutrient footprint describes the efficiency of nutrient use in a specific production chain and distinguishes virgin from recycled nutrients. The method was originally tested on oat flakes and oat porridge. Beef was chosen because previous Life Cycle Assessment (LCA) studies show it to have larger environmental impacts than those of plant and other animal products (Reijnders and Soret
2003; Williams et al.
2006; Carlsson-Kanyama and González
2009; Audsley and Wilkinson
2012; Leip et al.
2014). Most LCA studies compare different kinds of production systems and, therefore, stop at the farm gate. Some exceptions for beef exist (Carlsson-Kanyama and González
2009; Mieleitner et al.
2012; Opio et al.
2013; Rivera et al.
2014; Uwizeye et al. (
2016)), but to our knowledge, no studies exist on nutrient issues of animal products “from cradle-to-grave”, i.e. until waste management.
The nutrient footprint method developed by Grönman et al. (
2016) combines the amounts of nutrients captured [kg of N and P] for use in the production chain with the percentage of nutrients used [%], either in the primary product or in both the primary + secondary products. The captured nutrients are further divided into virgin and recycled nutrients. Virgin nutrients are extracted from nature and converted into a reactive form for the production chain studied (e.g. inorganic fertilisers), while recycled nutrients (e.g. manure, sewage sludge, secondary products of food processing industry), already captured in a previous production process, are recycled to the production chain studied. All phases of the production and consumption chain are included: from fertiliser production to human food product to wastewater treatment. The method offers information about nutrient use efficiency in a simple and comparable form. Thus, the nutrient footprint complements typical LCA studies on global warming, eutrophication and acidification potential.
Uwizeye et al. (
2016) developed a method similar to that of Grönman et al. (
2016) for NutUE which takes into account both N and P but stops at the end of the processing stage. In addition, it does not distinguish virgin from recycled nutrients or whether nutrients are captured for the primary product or for primary + secondary products. Erisman et al. (
2018) also developed a method for NutUE, but it considers only N. It also has a broader system boundary, not specifying different chains. A different concept of the nutrient footprint was presented by Leach et al. (
2012), who developed an N footprint tool which calculates annual per capita N losses to the environment caused by food consumption. For each food category, they defined a Virtual N factor which equals total N loss in the production chain divided by the N that remains in the consumed product. Similarly, Leip et al. (
2014) calculated N footprints of food products as direct N losses to the environment per unit of product; however, they excluded production chain phases beyond livestock slaughtering. Leip et al. (
2014) also developed an N investment factor, representing the total external N required to produce the N in one unit of product. These approaches, however, include only N and do not consider the recycling of nutrients from the latter life cycle phases of food consumption and wastewater treatment. Our approach, in contrast, gives a more holistic view of nutrient circulation in the food chain by combining nutrient use and emission data in all phases of the production chain until the treatment of human wastewater.
Annual beef production in Finland was 81 million kg in 2013, representing ca. 26% of total meat production (Luke statistics
2015a). Beef production has decreased 15% since 2003, while at the same time, total meat production has increased 4%. Annual beef consumption in 2013 was 18 kg per capita, corresponding to 100 million kg for the total population (Eurostat
2015; Luke Statistics
2015b). The share of beef in total meat consumption was 24% in 2013. From 2003 to 2013, beef consumption increased less than total meat consumption (4 and 11%, respectively). There are no statistics on the share of meat production originating from beef cattle, but the share of suckler cows in all cows (including suckler cows and dairy cows) was 17% in 2014 (Luke Statistics
2015c). Beef cattle production is relatively evenly distributed across Finland, although animal numbers are highest in Ostrobothnia and northern Savo, where dairy production is also concentrated. The case study was quantified using average data for a male calf originating from the Finnish suckler cow-calf system.
4 Discussion
The results show hotspots in the NutUEs of the beef production and consumption chain. For both N and P, NutUEs are lowest in the wastewater treatment phase. However, improvement in this phase is difficult to reach because the use of nutrients originating from wastewater sludge as fertilisers for crop production creates fears of contaminants ending up in food products. NutUE (N) was also relatively low during feed crop cultivation, indicating that N fertilisation was non-optimum. Precision farming and other measures to optimise N fertilisation to the level of plant requirements could improve NutUE (N).
Compared to oat flakes (Grönman et al.
2016), beef has lower NutUEs in the phases of crop production, food processing, supply and trade and consumption, as well as in the entire chain (Table
3). Beef’s lower NutUEs during crop cultivation are likely to be caused at least in part by the larger percentage of manure used as fertiliser. When manure is used, the farmers may not consider that some of the nutrients will be released after the current growing season (in subsequent years), and therefore, more nutrients are applied than what the crops need. Also, farmers normally estimate fertilisation rates based on optimal growing conditions and optimised yield potential, but these often do not occur, increasing the risk that excessive nutrients will be released to the air or water. Beef has lower NutUE than oat flakes in the consumption phase because energy consumption (and related nutrient losses during energy production) during oat flake preparation was excluded (Grönman et al.
2016). Likewise, beef has lower NutUE in the supply and trade phase because it is refrigerated, while oat flakes can be stored at room temperature, requiring no additional energy.
Table 3
NutUEs of nitrogen and phosphorus of beef (the present study) compared to that of oat flakes (Grönman et al.
2016), percentage use in the primary + secondary products
Crop production | 57 | 74 | 89 | 100 |
Food processing | 87 | 92 | 57 | 94 |
Supply and trade | 95 | 100 | 75 | 100 |
Consumption | 91 | 95 | 44 | 95 |
Entire chain | 47 | 71 | 75 | 99 |
The NutUEs of dairy cattle of Uwizeye et al. (
2016) (27–48% for N and 46–85% for P) lie in the same ranges as those in the present study (47% for N and 74% for P for primary + secondary products), despite the significant differences in the methods. Uwizeye et al. (
2016) consider NutUEs until the end of primary processing and include soil nutrient stocks, while the present study considers the entire chain and excludes soil nutrient stocks. Although their method may be more motivating for chain actors up to the end of primary processing, consideration of the entire chain provides a wider perspective for authorities as well as for actors beyond primary processing, such as operators of wastewater treatment plants and processors of recycled nutrients.
In the literature, few authors have estimated N use. Leip et al. (
2014) calculated an N footprint (direct N losses to the environment per kg carcass weight) and N investment factor of beef production systems in the European Union (EU) 27, using a farm gate system boundary, including slaughtering. In their study, the N footprint was ca. 500 g N/kg carcass weight, and N investment was 15–20 kg N/kg N in carcass weight. These values are relatively similar to those in the present study: 436 g N/kg carcass weight and 35 kg N/kg N in carcass weight.
According to Chatzimpiros and Barles (
2013), the N use efficiency (NUE) of cultivating feed crops on French beef farms was 76%. Their overall NUE of the livestock system (7.2%), calculated as total N in retail products divided by total N inputs, is higher than that in the present study (1.2% when the same phases of the food production chain—from production of agricultural inputs to food supply and trade—are considered). Chatzimpiros and Barles (
2013), however, averaged national beef production systems, while the present study considers only the suckler cow-calf system. According to Nguyen et al. (
2010), NUEs are generally higher in dairy bull-calf systems than in suckler cow-calf systems.
Leach et al. (
2012) and Pierer et al. (
2014) calculated Virtual N factors for beef. When calculated for only the slaughtered animal, the Virtual N factor for beef in the present study is about twice as high (12.9 vs. 8.5 in Leach et al. (
2012) and 5.4 in Pierer et al. (
2014)). When including the inputs and emissions allocated from the suckler cow as well, the Virtual N factor of the present study is ca. 5–8 times as high (45.6). The previous studies, however, averaged national beef production systems, while the present study considers only the suckler cow-calf system. Also, they did not include nutrient losses during fertiliser production.
In the literature, even fewer have estimated P use. Nguyen et al. (
2010) calculated N and P farm gate balances and efficiencies of typical beef production systems in the EU, including a suckler cow-calf system resembling the system in the present study (Table
4). They report slightly larger N and P balances (calculated as nutrients in imported fertiliser and feed inputs minus nutrients in live animals sold)—437.7 kg N and 12.4 kg P per 1000 kg slaughter weight—than those in the present study (401.9 kg N and 10.6 kg P per 100 kg slaughter weight). However, their NutUEs are higher than those in the present study as well (NutUE (N) 0.09 vs. 0.05, respectively, and NutUE (P) 0.5 vs. 0.34, respectively).
Table 4
Nitrogen and phosphorus inputs, outputs, balances and efficiencies in the present study and typical suckler cow-calf system in the European Union (Nguyen et al.
2010) presented as kg N and P 1000 kg slaughter weight
Slaughter weight, kg | 394 | 348 |
Age at slaughter, months | 19 | 16 |
N balance, kg | 401.9 | 437.7 |
N use efficiency | 5% | 9% |
P balance, kg | 10.6 | 12.4 |
P use efficiency | 34% | 50% |
The nutrient footprint offers information about the amount and efficiency of nutrient use in a simple and comparable form. In this sense, it is similar to the water footprint (Hoekstra et al.
2011), even though it does not consider relative access to the resource(s) in the same manner as the water footprint. Unlike water, however, nutrients are directly traded globally, and few regions are self-sufficient in nutrients.
Based on these calculations, the nutrient footprint seems to be a useful method for assessing nutrient use and its efficiency alongside other categories of potential impact, such as climate change and eutrophication potential. Current EC (European Commission) (
2013) LCA guidelines already recommend assessing depletion of resources such as water, minerals and fossil fuels alongside categories of potential environmental impact. One can expect to obtain a much clearer overall image of the ecological impacts of products and their flows by combining the nutrient footprint and other resource depletion methods with assessments of potential environmental impacts.
In mainstream LCA, only potential mid-point impacts on the environment are commonly considered, and there is no link to the overall sustainability and carrying capacity of ecosystems (Bjørn and Hauschild
2015). Recent discussion, however, has focused on whether limits of planetary boundaries should be taken into account (Steffen et al.
2015) to address such impacts (Sandin et al.
2015; Bjørn and Hauschild
2015). Steffen et al. (
2015) considered both N and P flows at current levels at high risk of substantially altering the resilience of Earth systems. Therefore, closer attention needs to be paid to nutrient use.