Comparing farming systems at crop rotation level by LCA

Transcription

1 In: Geerken, T., Mattson, B., Olsson, P. & Johansson, E., (eds.), Proceedings of the International Conference on LCA in Foods, Gothenburg. SIK, VITO, Gothenburg, Comparing farming systems at crop level by LCA T. Nemecek, C. Frick, D. Dubois, G. Gaillard Swiss Federal Research Station for Agroecology and Agriculture (FAL), CH-8046 Zurich- Reckenholz, Switzerland Abstract Life cycle assessments (LCA) of different farming systems have been mostly carried out at single crop level. However, farmers optimise their production for a whole crop. Moreover, some emissions like nitrate leaching occur mainly during the fallow periods between crops. It is therefore preferable to compare farming systems in the perspective of a crop. Three farming systems (medium intensive, extensified and low input) were assessed by LCA. Their environmental impacts differed by up to several hundred percents for single crops, but only between 1 % and 34 % for the crop, due to mutually compensating effects of the crops and the effect of grass-clover ley. The extensified and low input systems performed slightly better in the categories related to energy use, but worse in the categories influenced by the use of liquid manure. 1. INTRODUCTION The need to compare the environmental impacts of farming systems is increasing. Swiss agricultural policy supports integrated and organic farming systems by subsidies. Hence farming systems must be evaluated in order to show their environmental advantages. LCA has proven to be a valuable tool for the comparison of farming systems at crop level [1-2]. However, farmers usually grow a variety of crops and optimise their production over all these crops. Fertiliser and pesticide applications not only influence the target crop, but may have also effects on the subsequent ones. Some important emissions, like nitrate leaching, are difficult to attribute to a single crop. These problems can be circumvented by extending the system boundary to the whole crop, which has been done rarely [3]. In this paper we compare the evaluation of different farming systems first at the level of a single crop, second at the level of the crop and then the results of both approaches are compared. 2. GOAL AND SCOPE 2.1 Goal and study object Our goal is to compare the environmental impacts of arable crop production systems at different intensity levels. In this study the results from a field experiment in Central Switzerland (Burgrain, canton Lucerne) were used, where three farming systems are compared in a crop since 1991 [4-5]: intensive (IS), extensified (ES) and low input (LI). The intensive system is typical for the region. In comparison with other European countries it is only of medium intensity. In the extensified system the input of pesticides and mineral fertilisers is reduced, in the low input system, no use of mineral fertilisers is made, and pesticides are sprayed only exceptionally. We analysed the following six-year crop ( ): 1 st year: potatoes, followed by green manure in autumn, 2 nd year: winter, followed by a forage catch crop during winter, 3 rd year: grain, 4 th year: spring,

2 5 th and 6 th year: grass-clover ley. The crop is placed on six field plots, so that each crop is grown each year. 2.2 System boundary and allocation The system boundary includes all activities in the fields covered by the crop, plus the production of all inputs, namely: use of machines, including their production, transport, maintenance and the buildings required for their shelter, energy carriers: diesel, fuel for drying and electricity, production and transport of mineral fertilisers, production of pesticides, production of seeds, application of liquid and solid manure in the field. The production and storage of manure was allocated to animal production. Fertilisers and pesticides were fully allocated to the crop to which they were applied. The pesticides used were only active for a limited period and had hardly any effect on the following crops. The uptake of the nutrients N, P and K was higher than the fertilisation in all cases except for P and K in grain. Emissions occurring during fallow periods were not allocated to a single crop, but included in the LCA of the whole crop. For and straw an allocation was performed on the basis of the prices: 10 % of the environmental burdens of the production was allocated to straw and 90 % to the grains. 2.3 Functional units Agriculture has to fulfil multiple functions, which cannot be covered with a single functional unit. Therefore three functional units were used: 1. Area (hectare) represents the function of land use (social function) and shows the level of production intensity. 2. Dry matter yield (kg DM) represents the productive function of agriculture from the farmer s point of view. 3. Human nutritional energy (MJ) expresses the productive function of agriculture from the consumer s point of view. It takes into consideration that some products are directly consumed by humans, while others are used for animal feeding and produce human food as animal products [6]. The conversion of fodder to animal products reduces the energy content by about six times. Since no major differences were found in the results and conclusions based on different functional units, we show only the results per kg dry matter. Table 1: Key characteristics of the production inventories (mean values per year) of the three farming systems intensive (IS), extensified (ES) and low input (LI). Dry matter yield (kg DM/ha) IS ES % of IS LI % of IS Potatoes % % Winter % % % % % % Grass-clover % % Forage catch crop % % Average (crop ) % % Pesticides (kg active ingredients/ha) % % Mineral N fertiliser (kg N/ha) % 0 0% Liquid manure (m 3 /ha) % % Part of liquid manure given to arable crops 1% 34% 49% Solid manure (t/ha) % 9 74% Total available N (kg N/ha) % 71 68%

3 3. INVENTORY ANALYSIS The systems differed mainly in the quantities of fertilisers and pesticides applied (Table 1). Nevertheless, the overall differences in yields were comparatively small. Grass-clover ley (two years) contributed about half to the total dry matter yield and had as a result a big influence. Compared with similar trials, potato yields in the systems ES and LI were high. The soils were fertile and had high nutrient levels. Only mineral N fertilizers (IS and ES), solid and liquid manure were applied. The environmental inventories of agricultural inputs as well as the methods for the estimation of direct field emissions were taken from [6-7]. 4. IMPACT ASSESSMENT We applied the assessment methods listed in [7]. The impact assessment showed great differences between the three farming systems for crops considered individually. In most cases the systems IS and LI had the highest resp. lowest values, ES was intermediate. In some cases ES had the highest or lowest impact, but the differences were small. Hence we show only the values of the system LI relative to IS (Table 1). Table 2: Environmental impacts of the low input system (LI) in percent of those of the intensive system (IS) per kg dry matter. Impact category Potatoes Winter Energy use 90% 77% 95% 97% 99% 93% Greenhouse pot. (100 years) 98% 74% 105% 102% 85% 91% Greenhouse pot. (500 years) 96% 75% 104% 102% 89% 92% Ozone formation 98% 89% 106% 112% 96% 99% Human toxicity 100% 92% 108% 116% 99% 101% Aquatic ecotoxicity 193% 143% 133% 231% 75% 110% Terrestrial ecotoxicity 1456% 1213% 159% 713% 74% 116% Aquatic eutrophication 149% 147% 178% 180% 80% 120% Terrestrial eutrophication 503% 506% 317% 364% 88% 134% Total eutrophication 133% 84% 142% 141% 93% 108% Acidification 363% 415% 294% 328% 88% 132% Large differences in the environmental impacts between farming systems were found for single crops (up to a factor of 15), but only small ones at the crop level (up to 34 %). The two main reasons for these different results were the distribution of liquid manure and the effect of the grass-clover ley. Liquid manure was distributed in a different manner: in the system IS almost all liquid manure was applied to the grass-clover ley and the catch crop, whereas in the system ES one third and in the system LI even one half of the liquid manure was given to the arable crops (Table 1), which partly replaced the mineral fertilisers. Consequently, ecotoxicity, eutrophication and acidification of the arable crops were higher in the LI-system, but were compensated by lower impacts of the grass-clover ley. The contrary was true for the system IS, the system ES being intermediate. The second reason for the small differences at crop level was the equalising effect of the grass-clover ley and the catch crop: they contributed more than 50 % to the total dry matter yield and largely influenced the results. Their yields (Table 1) and most of their environmental impacts (Table 2) were similar for all farming systems. The use of fossil energy largely differed between the crops (Figure 1). However, the differences due to the farming system were comparatively small. Potatoes had a high energy consumption per kg DM, due to an intensive use of machines and to a high energy demand for the seed production. In grain, half of the energy was consumed by the drying process. The cereals and were at a similar level. The grass-clover ley had the lowest

4 energy demand per kg DM of all crops. The results for greenhouse potential, ozone formation and human toxicity were closely related to energy use and similar to those shown in Figure 1. 5 Energy use [MJ eq./kg DM] Pesticides Min. fertiliser prod. Seed Energy carriers Machines Buildings 0 IS ES LI IS ES LI IS ES LI IS ES LI IS ES LI IS ES LI Potatoes Winter Figure 1: Energy use per kg DM of the different crops and the whole crop in the farming systems intensive (IS), extensified (ES) and low input (LI). 0.6 Aquatic ecotoxicity [g Zn eq./kg DM] IS ES LI IS ES LI IS ES LI IS ES LI IS ES LI IS ES LI Pesticides Field emissions Min. fertiliser prod. Seed Energy carriers Machines Buildings Potatoes Winter Figure 2: Aquatic ecotoxicity potentials per kg DM of the different crops and the whole crop in the farming systems intensive (IS), extensified (ES) and low input (LI). Aquatic ecotoxicity potentials (Figure 2) were highest for potatoes and grain. They were dominated by the applications of the fungicides chlorothalonil and copper in potatoes and by the heavy metals contained in solid manure (field emissions in Figure 2) in. In arable crops the system LI showed the highest values. In contrast, the system IS had the highest impact in grass-clover ley. These two effects compensated themselves, so that the overall result at crop level was almost the same. It must be emphasised that the assessment method CST95 [8] applied for toxicity gives a high weight to heavy metals in comparison to pesticides. Nevertheless, the results show that the choice of the active ingredients is very im-

5 portant: chlorothalonil seems to be a critical substance and should therefore be used scarcely. The results for terrestrial ecotoxicity, eutrophication and acidification look similar to Figure 2, except that pesticides played an important role for aquatic ecotoxicity only in potatoes. The results for the functional unit MJ nutritional energy are similar to those shown above. Due to the differences in yields, the impacts related to energy use were more accentuated, when calculated per hectare, but smaller for the impact categories related to the use of liquid manure (ecotoxicity, eutrophication and acidification). 5. INTERPRETATION AND CONCLUSIONS The study shows that the comparison of farming systems may yield misleading results, when performed only at the level of a single crop. The system boundaries should therefore be extended to a whole crop. Differences detected for single crops may be almost fully compensated when the whole crop is considered. The differences in yields between the systems were relevant for single crops, but rather small over the whole crop. The environmental impacts showed the same tendency, sometimes in the opposite direction. In the extensification process the input of fertilisers and pesticides was reduced. In contrast, there was little difference in the use of infrastructure (machines, buildings) and diesel, which largely determined the energy consumption and related impacts. Fertilisers and pesticides had only a limited influence on the LCA compared to manure, which was the key factor for ecotoxicity, eutrophication and acidification. When the aim is to improve agricultural systems ecologically by extensification, we should consider not only pesticides and mineral fertilisers, but also the use of machines and manure. Given the regional specificity of the crop and the high level of nutrients available from the soil (little fertilisation required), care must be taken, when generalising these results to other agricultural systems. 6. REFERENCES 1. E. Audsley, S. Alber, R. Clift, S. Cowell, P. Crettaz, G. Gaillard, J. Hausheer, O. Jolliet, R. Kleijn, B. Mortensen, D. Pearce, E. Roger, H. Teulon, B. Weidema and H. van Zeijts. Harmonisation of life cycle assessment for agriculture. Final Report, Concerted Action AIR3-CT European Commission DG VI Agriculture, G. Gaillard und J. Hausheer. Ökobilanz des Weizenanbaus. Agrarfoschung, 6 (1): 37-40, Th. Alföldi, O. Schmid, G. Gaillard und D. Dubois. IP- und Bio-Produktion: Ökobilanzierung über eine Fruchtfolge. Agrarfoschung, 6 (9): , D. Dubois, U. Zihlmann, P.M. Fried, R. Tschachtli und O. Malitius. Burgrain: Erträge und Wirtschaftlichkeit dreier Anbausysteme. Agrarforschung 6 (5), , C. Frick, D. Dubois, T. Nemecek, G. Gaillard und R. Tschachtli. Burgrain: Vergleichende Ökobilanz dreier Anbausysteme. Agrarfoschung, 8 (4): , D. Rossier: Adaptation de la méthode écobilan pour la gestion environnementale de l exploitation agricole, Rapport SRVA, 49p., D. Rossier et G. Gaillard. Bilan écologique de l exploitation agricole: méthode et application à 50 entreprises. Rapport SRVA, FAL sur mandat de l Office fédérale de l agriculture, O. Jolliet and P. Crettaz. Critical Surface-Time 95 - a life cycle impact assessment methodology including fate and exposure, ETH Lausanne, Institute of Soil and Water Management, Lausanne, 1997.