Evaluating the environmental profiles of winter wheat rotation systems under different management strategies

Evaluating the environmental profiles of winter wheat rotation systems under different management strategies Sara González-García a,b, ⁎, Fernando Almeida c,d , Maria Teresa Moreira a ,MiguelBrandão b a CRETUS Institute, Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain b Department of Sustainable Development, Environmental Science and Engineering (SEED), KTH - Royal Institute of Technology, Stockholm, Sweden c Grupo Da Cunha, 15175 Carral, Spain d Department of Analytical Chemistry, Faculty of Sciences, Universidade de Santiago de Compostela, 27002 Lugo, Spain HIGHLIGHTS •Nine wheat rotations with alternate crops (potato, maize and rapeseed) were assessed. •The best land management systems per hectare and €were identified. •Arable operations are critical contributors to the environmental profile. •Carbon storage in the soil when returning straw involves environmental credits. •Results are quite sensitive to the delimitation of the system boundary. GRAPHICAL ABSTRACT abstractarticle info Article history: Received 9 December 2020 Received in revised form 13 January 2021 Accepted 14 January 2021 Available online 21 January 2021 Editor: Damia Barcelo Keywords: Attributional LCA Bread Crop rotation Integrated assessment Maize Potato Oilseed rape Climate change poses a remarkable challenge to global food security, for which wheat is one of the main staple agricultural commodities. The cultivation of different varieties of winter wheat in Galicia (commercial and native) under rotation systems with potato, maize and oilseed rape was evaluated from an environmental point of view. The general approach of this study included the gathering of the inventory data of the different crops, the quantification of their environmental impacts and economic benefits, to identify the best land management system. Life Cycle Assessment (LCA) was used as environmental tool. The environmental profiles of each rotation system were reported in terms of nine impact categories. Crop rotations were analysed both per hectare and per €of gross margin, so that the information can be relevant to land-management decisions. Preference ranks were established based on an environmental normalized score for both units. The results suggest that arable operations contribute decisively to the environmental profile of the rotations. The avoided mineral fertilization processes, the carbon storage in the soil when returning straw to the field, as well as the electricity production clearly influence the environmental impact of the rotations. Scenarios that include native wheat under organic management are always the environmentally preferred ones while the preferred alternate crop depends on the reference unit. Concerning the margin gross, scenarios including the native variety report the highest profits, being the potato the preferred alternate crop. Further assessment needs to be undertaken to identify differences in the results of different ways of conducting LCA, i.e. attributional vs consequential approaches. © 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Science of the Total Environment 770 (2021) 145270 ⁎Corresponding author at: CRETUS Institute, Department of Chemical Engineering, School of Engineering, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain. E-mail address: [email protected] (S. González-García). https://doi.org/10.1016/j.scitotenv.2021.145270 0048-9697/© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv 1. Introduction Climate change is already having profound consequences on biodiversity because of the increaseof carbon emissions. The adverse impacts of climate change represent a potentially considerable challenge to global food security (Mäkinen et al., 2018;Li et al., 2020). In this regard, agriculture is arguably the sector most affected by climate change. The relationship between climate change and crop production depends largely on when and what mitigation and adaptation actions are adopted. Cereal grains and tubers are the most common food staples. The world produces about two billion tonnes of cereals annually for human food or livestock feed (Oteros et al., 2015). Cereals provide high levels of carbohydrates, dietary fibre and protein. Among cereals, wheat is the most widely cultivated plant in the world (Le Gouis et al., 2020;Campo de Tejada, 2020) and is considered a key crop in the context of food security (Erice et al., 2019). More than 200 Mha in the world are dedicated to wheat cultivation due to its significant commercial importance (pasta, couscous, bread and bulgur are wheat products) (Câmara-Salim et al., 2020). In addition, wheat grain and its products provide 18% of the food calories ingested by the world population (Erice et al., 2019). In 2018, this crop constituted 43% of the cereal produced in the EU (Eurostat, 2020), which is the largest producer in the world (Xynias et al., 2020). Spain is a major producer of cereals (24.5 Mt and 6 Mha in cereal production in 2018), where wheat and barley are the most produced (SAAFFM, 2018). There are several types of wheat, the most cultivated beingcommon wheat (Triticum aestivum L., ssp. aestivum) and durum wheat (Triticum turgidum ssp. durum Desf.). Common wheat is mainly used to produce flour for bread due to its higher fermentation capacity. On the contrary, durum wheat is dedicated to pasta production due to its higher protein content.The production of common wheat in Spain is much higher than that of durum wheat, which is grown mainly in other Mediterranean countries such as Italy. The average annual production of Spain is 12 Mt for the former and 1 Mt for the latter (Campo de Tejada, 2020). The quality of wheat depends not only on the variety used but also on its ability to accumulate protein reserves in the grain, which is determined by nitrogen fertilization (Hellemans et al., 2018). It is therefore necessary to pay special attention to effective fertilization protocols, mainly in humid Mediterranean areas (Blandino et al., 2020). In many countries, intensive crop production has depleted soil fertility, jeopardizing its long-term productive capacity and consequently its ability to meet the needs of future generations. Intensification has led to many environmental issues, such as high consumption of non-renewable energy resources, loss of biodiversity and pollution of the aquatic environment by leaching. Mineral fertilizers are the main source of nutrients, although the contribution of animal manure remains significant in areas where livestock are present. More than 50% of the nitrogen applied to the soil is not used by the crop plant and may be taken up by the soil microbiome (Liu et al., 2016). Nitrogen is directly lost as nitrous oxide (N 2 O) and through volatilization (ammonia, NH 3 and nitrogen oxides, NO x ) or leaching (nitrate, NO 3 − )(Pan, 2016;Liu et al., 2016; Wowra et al., 2020). The loss of nitrogen in its different forms can have a detrimental impact on living organisms (Habermeyer et al., 2015) and has a negative effect on the environment by causing eutrophication of freshwater and marine ecosystems (Nemecek et al., 2015) gas and global warming (Nemecek et al., 2011a;Goglio et al., 2012), among others. Therefore, nitrogen management is shown to be a key driver of the environmental impacts of agricultural systems. Reducing environmental impacts from agriculture requires an understanding of how alternative agricultural production systems and the efficiency of agricultural inputs drive environmental degradation. Sustainable production relies on an integrated agriculture that optimizes nutrient and pest-and-disease protection through integrated nutrient and pest management. In this context, crop rotation, aligned with practices that enhance the activity of beneficial soil microorganisms, can regulate the biogeochemical soil cycles and affecting soil fertility (Watts-Williams and Cavagnaro, 2018; Mäkinen et al., 2018;Hendrickson and Colazo, 2019). Crop rotation consists of growing different crops (cereals, root crops, rapeseed, legumes) in sequence on a field in 4–6 year cycles that also include cover/catch crops. According to Ghaley et al. (2018),croprotation reportsthegreatestpositiveeffectonbiomassyieldsand,nutrient retention and cycling in comparison with monoculture. The design of environmentally efficient crop rotations requires a comprehensive tool that allows the assessment of the different environmental impacts caused directly by the cropping systems, as well as those arising because of the inputs used. The Life Cycle Assessment (LCA) methodology has been widely applied to quantify and compare the environmental impacts of agricultural systems (González-García et al., 2013, 2016; Nemecek et al., 2011b, 2015;Noya et al., 2015, 2017;Pishgar-Komleh et al., 2019;Salim et al., 2019). This methodology aims at identifying possible reductions of environmental impacts by identifying improvements in the systems analysed. Moreover, by accounting for different life cycle phases, shifts in environmental burdens between life cycle stages can be avoided. The cultivation of different varieties of winter wheat in Galicia (NW Spain) under rotation systems with potato, maize and oilseed rape was environmentally analysed in this study. The interest in the cultivation of wheat in this Spanish region is due to the fact that its production is expected to double in the next few years due to the Protected Geographical Indication 1 granted to Galician bread as a quality reference at national level. This bread presents a distinct flavour and taste due to its differentiated production scheme, based on the use of sourdough and the requirement for longer fermentation times and baking in stone ovens (CâmaraSalim et al., 2020). The general approach consisted in gathering the inventory data of the different crops, which allowed for the quantification of their environmental effect, as well as identifying the environmental hotspots. For the first time, such different crop rotation systems based on wheat have been analysed from both environmental and economic perspectives. Finally, the most favourable land management system will be identified, being the one that reports the greatest economic revenue and the least environmental impact, considering that rotation systems give rise to different co-products (wheat grain, wheat straw, tubers, maize silage and oilseeds). 2. Materials and methods In this study, LCA methodology was used to evaluate the environmental impacts of different cropping systems under rotation regimes to produce winter wheat grain for bread. The international standards ISO 14040 (ISO, 2006a) and 14044 (ISO, 2006b) were followed in detail. Differentways ofperforming LCA can be used to assess the environmental profiles of product systems, i.e., attributional or consequential, and LCA results are highly dependent on the LCA approach taken, which determines the delimitation of thesystem boundaries. In Attributional LCA (ALCA), all inputs and outputs of a production system are attributed to the functional unit by linking and/or partitioning the unit processes of the system according to a normative rule (e.g., allocation factors based on economic, mass or energy values, among others). In Consequential LCA (CLCA), all activities in a production system are linked so that they are included in the production system to the extent that they are expected to change because of a change in demand for the functional unit (Ekvall, 2020). There is a strong connection between the selected methodological approach and the way co-products are handled in multi-output activities. Since average data were available and the focus of this study was really to describe the environmentally relevant physical flows within a time window, but not to describe how environmentally relevant flows will change in the future in response to possible decisions, the ALCA methodology was adapted. 1 https://www.mapa.gob.es/es/alimentacion/temas/calidad-diferenciada/ publicsolicitregistroydudouec2433de19072019_tcm30-524594.pdf. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 2 2.1. Goal and scope definition The main goal of this study was to perform a comprehensive environmental and economic analysis of the different cropping systems destined mainly to the production of winter wheat (Triticum aestivum L.) and considering three different crop rotations. Regarding wheat crops, two varieties were considered: commercial and autochthonous (Galician). Commercial winter wheat under conventional management (C-WW), Galician winter wheat (“trigo del país”,Caaveiro variety) under conventional management (GcWW) and Galician winter wheat under ecological management (Ge-WW) in three different six-year rotation cycles were considered. The crops evaluated were winter wheat with maize (Zea mays L.), winter wheat with oilseed rape or rapeseed (Brassica napus L.) and winter wheat with potato (Solanum tuberosum L.). Cropping systems were arranged in 40 ha plots per whole rotation located in Galicia (NW Spain), covering an area of 450 ha and correspond to 51 farmers. The regions under analysis (Carral, Laracha and Xinxo) represent a population of around 27,000 inhabitants and 300 km 2 of surface area. The nine scenarios differed in terms of soil tillage, use of agrochemicals (including mineral and organic fertilizers and other agrochemicals such as herbicides, fungicides and insecticides), biomass yields and economic revenue. Table 1 details the nine 6-year crop rotation cycles based on winter wheat (C-WW, Gc-WW and Ge-WW) with potato (P), maize (M) or oilseed rape (OSR) as co-products. The croplands under study were dedicated to agriculture in the last 20 years, producing arable crops, mainly wheat. The experimental plots were set in regions where the climate is oceanic with coastal, Mediterranean, inland and mountain variants. The average annual precipitation in the area is 750–1000 mm, concentrated mainly in autumn and winter. Regarding the soil, the clay content is 4.9%, pH is 5 and the soil organic carbon (SOC) content is around 55 tC·ha −1 in the upper 30 cm. As for the scope of the study, it was conducted from a cradle-to-farm gate perspective. For each crop rotation system, the system included the production of all inputs, such as machinery, agrochemicals, seeds and diesel, as well as their use (i.e., the operation of machinery in the field) and the corresponding direct emissions (i.e., combustion emissions from diesel use and direct field emissions from agrochemicals application). Regarding the system boundaries for each rotation system, the rotation began after the harvest of the previous crop and ended with the harvest of the last crop (rotations of 6 years). Furthermore, hotspots identification was performed, which implies the identification of the elements or activities within the agricultural systems that contribute most to a certain impact category. Table 1 Crop rotation cycles of 6 years under study (S i ) and main yields. C-WW: Commercial winter wheat; Gc-WW: Galician winter wheat (native variety) –conventional management; Ge-WW: Galician winter wheat (native variety) –ecological management; P: Potato; M: Maize; OSR: Oilseed rape. Year Main crop (WW) Alternate crop Scenario 123456 t grain·ha−1 t straw·ha−1 t·ha−1 €· ha−1 S1 CWW1 CWW2 P1 CWW1 CWW2 P1 22.00 7.48 70 15,354 S2 CWW3 M1 CWW3 M1 CWW3 M1 15.60 5.30 90 8891 S3 CWW4 OSR1 CWW4 OSR1 CWW4 OSR1 15.00 5.10 10.50 6507 S4 GcWW1 GcWW2 P2 GcWW1 GcWW2 P2 11.20 – 70 14,910 S5 GcWW3 M2 GcWW3 M2 GcWW3 M2 8.10 – 90 8640 S6 GcWW4 OSR2 GcWW4 OSR2 GcWW4 OSR2 7.50 – 10.50 6150 S7 GeWW1 GeWW2 P3 GeWW1 GeWW2 P3 10,00 – 40 14,900 S8 GeWW3 M3 GeWW3 M3 GeWW3 M3 6.60 – 75 9918 S9 GeWW4 OSR3 GeWW4 OSR3 GeWW4 OSR3 6.00 – 7.50 5880 Yellow color - wheat; Orange color - Maize; Green color - Potato; Blue color - Oilseed rape. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 3 2.2. Functional unit and allocation It is important to consider the multifunctionality of each agricultural system under study, which requires an analysis that considers alternativefunctionalunits. The maingoal forthe farmers, andthusthefunction of this study, is to maximize the productionof wheat grain. Nevertheless, each cropping system yields additional products (straw, potatoes, maize silage or rapeseed) with industrial or agricultural uses and thereby provides an additional economic benefit. According to the literature (e.g. Deytieux et al., 2012;Nemecek et al., 2011a, 2011b;Goglio et al., 2012; Pishgar-Komleh et al., 2019), the results and thus, the decision supported by farmers and consumers differs considerably when expressed as a land-based unit, a biomass-based unit or an economic based unit. Therefore, in this study the hectare of land (ha) was used as base functional unit. This unit gives farmers an idea of how to manage their land to minimize environmental impacts. It also provides an answer to the question: What is the best use of land from an environmental perspective, regardless of the crops grown or revenue obtained? In addition, the discussion of the results incorporated the profiles of each rotation system in terms of gross margin. The gross margin is estimated by discounting the total production costs (including costs of activities and inputs) to the total income from the sales of products. This reference unit gives an idea of the environmental burdens on the economic revenue from agricultural activities. Therefore, in this case, the goal is to minimize the impact per €. This unit gives an answer to the question: What is the rotation system that produces the greatest economic benefit for the farmer with the least environmental impact? Since the comparison is made at the crop-rotation level, no allocation is needed. 2.3. Description of the cropping systems under assessment The agricultural systems analysed are dedicated to the production of winter wheat considering the two varieties mentioned: commercial and native. Both varieties are different not only in terms of production capacity and agrochemical requirements, but also in terms of chemical composition. In this regard, the native variety reports a higher protein content and a lower starch content than the commercial variety. Crop rotations with potato,maize and oilseed rape are considered. As a result, nine crop rotation scenarios were designed. The set of crop rotations included those typically practiced in the region (e.g., maize and potatoes), but also new crop rotations that are rarely practiced, but that have potential to be incorporated, such as oilseed rape. As a result, a total of 9 crop combinations were considered: S1: (C-WW1 + C-WW2 + P1) x2; S2: (C-WW3 + M1)x3; S3: (C-WW4 + OSR1)x3; S4: (Gc-WW1 + Gc-WW2 + P)x2; S5: (Gc-WW3 + M2)x3; S6: (Gc-WW4 + OSR2)x3; S7: (Ge-WW1 + Ge-WW2 + P3)x2; S8: (Ge-WW3 + M3)x3; S9: (Ge-WW4 + OSR3)x3 as shown in Table 1. Regardless of the varieties, the activities performed for each crop were classified into three main stages, which are field establishment, crop growth and biomass harvesting. All these stages included different processes which have been identified in detail for each crop. To do so, specific questionnaires were designed to identify not only the operations and machinery involved but also the demand of inputs from farmers. Agricultural activities start with the field establishment stage, where the soil is prepared for sowing. Crop-growth related activities include the application of fertilizers and other agrochemicals (i.e., pesticides, insecticides, fungicides), and mechanical treatment. Finally, the biomass-harvesting stage includes harvesting and additional activities, such as baling and transport to storage in silos, if necessary. To delimit the activities for a specific crop in a rotation system, the interval considered for each crop started after the harvest of theprecedingcrop and endedwiththe harvest of the main crop. Therefore, anyperiod between the harvesting of a crop and soil tillage activities of the next crop was attributed to the latter. Nevertheless, it is important to note that there are some gaps in LCA methodology applied to agricultural systems specifically in crop rotation systems, since there are some interactions between the individual crops of the rotation that could be neglected if the crops are assessed individually. 2.3.1. Winter wheat cropping systems 2.3.1.1. Commercial winter wheat cultivation (C-WW). The cultivation of the commercial variety starts with mouldboard ploughing before the application of a complex mineral fertilizer (8N-15P-15K). Secondly, the soil is tilled, and seeds are sown (200 kg·ha −1 ) in November. During crop growth, there are four applications of agrochemicals: chlortoluron and diflufenican (pre-emergence herbicide treatment), tribenuronmethyl and pinoxaden (post-emergence herbicide treatment), calcium ammonium nitrate (mineral fertilization) and tebuconazole (fungicide treatment). Finally, biomass is harvested in August. The grain is separated from the straw. While 15% of the latter is left in the field, the remaining 85% is sold for bedding and cattle feed, so a baling process is required. 2.3.1.2. Cultivation of native Galician winter wheat in conventional regime (Gc-WW). The cultivation of the Galician variety under conventional conditions is less intensive in terms of agrochemical requirements and agricultural activities. Field establishment requires mouldboard ploughing and milling before sowing (150 kg seeds·ha −1 )inNovember.Aftersowing and before the harvest, three agrochemicals are applied: herbicide (chlortoluron and diflufenican), mineral fertilizer (calcium ammonium nitrate) and fungicide (tebuconazole). In this crop, all the wheat straw is left in the field as nutrients supplier for the next crop in the rotation system. 2.3.1.3. Cultivation of native Galician winter wheat in organic regime (Ge-WW). Following the principles of organic agriculture, cultivation is aimed at minimizing the use of inputs and there is a strict limitation on the use of synthetic pesticides and mineral fertilizers. Thus, the use of mineral fertilizers, herbicides, fungicides or insecticides has not been considered in the cultivation of the Galician variety under the organic regime. The fieldispreparedbeforesowingby chisel ploughing (more superficial than mouldboard ploughing) and organic fertilization is carried out with poultry manure (supplied by ecological farms). Sowing (150 kg seeds·ha −1 ) is combined with soil tillage. Before harvesting (also in November), two treatments are performed: the first one is a mechanical treatment to remove weeds, since there is no pesticide application, and the second one consists of the application of a foliar fertilizer (Nitromyel 30-00) applied directly to the leaves of the plants, which is suitable for ecological regimes. In this crop, all the wheat straw is left in the field and only the grain is obtained as product. In all winter wheat case studies, sun drying is the drying method for reducing the moisture content of the grains (finally the moisture content is around 12%). The dried grains are then stored in silos for one year before being sold to bread producers. The crops are rain-fed so there is no irrigation equipment involved. The agronomic inputs for each crop growth (C-WW, Gc-WW and Ge-WW) are shown in Tables SM1–SM3 in the Supplementary Material, where the features of the specific agricultural machines commonly used for these crops are summarized. The use of crop residues as mulch has numerous benefits for the soil and the environmentdue to their content of nutrients such as N, P and K, as well as C, which can nourish the subsequent crop in the rotation as explained in Section 2.4.1.Table 1 shows the different combinations for WW cultivation. C-WW1, Gc-WW1 and Ge-WW1 were modelled after potato as the preceding crop and did not receive any input of straw. Conversely, C-WW2, Gc-WW2 and GeWW2 were modelled after WW as a preceding crop and received wheat straw (15% in C-WW2 and 100% in the others). Regarding WW crops cultivated under rotation with maize and oilseed rape (C-WW3, C-WW4, Gc-WW3, Gc-WW4, Ge-WW3 and Ge-WW4), they received straw from the preceding crops. As a result, nine different scenarios were defined. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 4 2.3.2. Crop rotation systems As detailed above, nine different rotation systems were formulated based on the combination of winter wheat (WW) with potato, maize or oilseed rape. The C-WW and Gc-WW rotations showed no difference in cultivation practices, as both were under conventional management and, therefore used agrochemicals. Conversely, in the rotations including Ge-WW, specific organic fertilizers were applied. All nine scenarios were cultivated in a six-year rotation cycle. Scenarios S1-S6 were performed under conventional management and S7-S9 under anecological regime. A six-year rotation cycle based on WW and potato (S1, S4 and S7) consisted of two continuous years of WW (year 1, year 2, year 4 and year 5) followed by one year of potato (year 3 and year 6). Regarding the six-year rotation cycles based on WW with maize (S2, S5 and S8) and oilseed rape (S3, S6 and S9), they were alternately cultivated, i.e. one year of WW is followed by one year of the alternate crop (maize or oilseed rape), as detailed in Table 1. 2.3.2.1. Potato under conventional management (P1 and P2). Potato cultivation under conventional management is considerably mechanical, involving multiple soil preparation activities, the application of mineral fertilizers (NPK 9-18-27 and calcium ammonium nitrate) and other agrochemicals (up to seven) as detailed in Table SM4 in the Supplementary Material. Field establishment requires mouldboard and chisel ploughing, as well as a mineral fertilization and milling before sowing (1200–1500 kg seeds·ha −1 ) in May. It is important to note that the cultivation of potatoes receives 15% and 100% of the wheat straw produced in C-WW2 (P1) and Gc-WW2 (P2), respectively. Harvesting is performed in September and the biomass yield is on average 35 t·ha −1 (80% moisture), of which 10% is used for animal feed since it does not meet the quality requirements for human consumption. 2.3.2.2. Maizeunder conventional management (M1 and M2). The production of maize silage under conventional management is detailed in Table SM5 in the Supplementary Material. It requires large amounts of mineral fertilizers (NPK 8-15-15 and calcium ammonium nitrate) and agrochemicals, and numerous agricultural activities such as mouldboard and chisel ploughing and soil tillage. Sowing is performed in May and this activity is combined with the application of an insecticide. The harvest is done in October and the average yield is about 30 t·ha −1 of maize silage (70% moisture content) which is baled. In addition, 5 t·ha −1 (15% moisture content) of the maize straw is left on the field as nutrient supplier for the following crops in the rotation (i.e. C-WW3 and Gc-WW3). However, the cultivation of maize also receives an input of wheat straw from previous crops: 15% from C-WW3 (in M1) and 100% from GcWW3 (in M2). 2.3.2.3. Oilseed rape under conventional management (OSR1 and OSR2). The production of oilseed rape requires fewer agricultural activities than potatoes or maize. Sowing (4 kg seeds·ha −1 ) is performed in September (combined with soil tillage) after chisel ploughing and mineralfertilization withNPK(8-15-15). There isapost-emergence mineral fertilization with calcium ammonium nitrate and application of herbicide. Finally, harvesting is in July and the average yield is 3.5 t oilseeds·ha −1 . The straw produced (9 t·ha −1 , 20% moisture content) is left entirely in the field as a nutrient supplier for the next crop in the rotation system (i.e. winter wheats C-WW4 and Gc-WW4). The crop also receives straw from the previous crop (15% and 100% of the straw produced in C-WW4 (for OSR1) and in Gc-WW4 (OSR2), respectively). A summary of the agricultural activities involved is detailed in Table SM6 in the Supplementary Material. 2.3.2.4. Potato, maize and oilseed rape under ecological management (P3, M3 and OSR3). Changes in soil quality and productivity can provide critical signs of environmental degradation. In this regard, changes in soil structure through conventional agricultural management practices (use of agrochemicals and intensive agricultural activities) intensify surface runoff, loss of nutrients and soil to water bodies. Incorporating ecological management into intensive farming systems can improve soil quality with sustained productivity (Bhardwaj et al., 2011). Organic farming involves the production of a crop without the use of synthetic chemical fertilizers and maximises the use of ecological interactions. Three rotation systems include ecological management which are S7S9, where Ge-WW is combined with P3, M3 and OSR3, respectively. Considerable differences from conventional management can be identified for each alternative crop. In the case of potato (P3, see Table SM7 in the Supplementary Material), the main difference is the application of an organic fertilizer (poultry manure from organic farms) and a mineral fertilizer (PatentKali 30%) which is allowed in organic crop production. Moreover, there are fewer applications of insecticides and fungicides but there is an additional mechanical treatment to remove weeds. The cultivation of potatoes under ecological management (P3) receives an input of wheat straw (100%) from the previous crop Ge-WW2. The yield of the potatoes is considerably reduced to 43% (20 t·ha −1 , 80% moisture where 10% is destined to animal feed). Concerning organic maize (M3, see Table SM8 in the Supplementary Material), mineral fertilizers are substituted by two applications of ecological manure (poultry and cattle) before sowing. Only one mechanical treatment and one insecticide treatment are carried out before harvesting. The cultivation of maize under ecological management (M3) receives an input of wheat straw (100%) from the previous crop Ge-WW3. The maize silage yield is 25 t·ha −1 and 2.5 t·ha −1 of maize straw is left on the field. Finally, the cultivation of ecological oilseed rape (OSR, see Table SM9 in the Supplementary Material) includes two organic fertilizations with ecological manure before sowing, which is combined with soil tillage. After sowing, there is a mechanical treatment, removingthe use of agrochemicals. The cultivation of OSR under ecological management (OSR3) receives an input of wheat straw (100%) from the previous crop GeWW4. The oilseeds yield is 2.5 t·ha −1 . 2.4. Life cycle inventory analysis and assumptions Fig. 1 illustrates the boundary of the agricultural systems at farm gate. The life cycle assessment of each crop in the rotation comprised the extraction of raw materials (e.g. fossil fuels and minerals), manufacture (e.g. seeds, mineral fertilizers, herbicides, insecticides, fungicides and agricultural machinery), use (tailpipe emissions and tyre abrasion emissions), maintenance and final disposal of the machines. Information regarding operation hours, diesel consumption, amounts of agrochemicals applied and yields of products and by-products was provided directly by farmers through surveys and interviews. This information is summarized inTables SM1–SM9 in the Supplementary Material and corresponds to primary data for the foreground systems. The calculation of the machinery used (tractors, trailers and implements) in each agricultural activity was carried out according to the Ecoinvent database® considering the weights, operation hours and lifetimes of the machinery. Although the use of primary data is recommended, it was necessary to consider secondary data to complete the inventory tables. Secondary data were handled for the background system that comprises the activities required to produce all the inputs to the farming systems (i.e. diesel, machinery, agrochemicals), as well as to estimate the tailpipe emissions. The Ecoinvent® database version 3.5 (Wernet et al., 2016) was considered as the main secondary data source. For the application of manure in the organic regime (S7-S9, see Table 1), poultry and cow manure were considered. Both come from farming activities which are multifunctional activities. Bearing in mind the information supplied by farmers, 50% of the manure must be used for energy purposes on poultry and dairy farms, with the remaining 50% derived from fertilization when the organic regime is established and receiving an economic revenue from this procedure. Consequently, the environmental burdens resulting from agricultural activities were S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 5 shared among the co-products (manure, electricity and animal products) according to an economic allocation approach. To this end, the economic data provided by the farmers involved were managed. Consequently, a factor of 1.0% was established for poultry manure considering the inventory data of the poultry farm of Gonzalez-Garcia et al. (2014). Concerning the dairy farm,an allocation factor of 4.1%wasestimatedfor the cow manure considering inventory data from Cortés et al. (2020). 2.4.1. Effect of crop residues and land use Approximately, 9% of global carbon emissions derive from land use changes. Despite the common practice of excluding LUC emissions in the LCA of agricultural products (Schmidt et al., 2015), it is a relevant source of impacts to include when assessing agricultural systems, particularly because the results vary considerably. There are two types of land use change caused by land occupation: direct land use change (dLUC) and indirect land use change (iLUC). The dLUC is associated with changes in the carbon content of biomass and soil and iLUC refers to those carbon changes that occur indirectly elsewhere (Schmidt et al., 2015). Both LUCs have been considered in our system boundaries considering the changes in soil carbon content due to straw being returned into the field, asdetailed above. In our study, a single emission factor has been estimated for iLUC under an attributional LCA approach for agricultural land of 289 kg CO 2 eq·ha −1 of agricultural land used per cropping system over a period of 6 years, which was estimated based on a biophysical seven steps-model developed by Schmidt et al. (2015). During WW in S4-S9 only grain was harvested, while straw was left in the field. In S1-S385% of the strawwas baled and collected for animal feed, while the remaining 15% was left in the field. For rapeseed and potatoes, only seeds and tubers were collected, respectively, while crop residues (straw and leaves) had the same fate as wheat straw in S4S9. In the case of maize, the main product is the silage, so whole maize plants were removed, although a small amount of biomass was left in the field, as described above. The straw returned to the field modifies the soil organic composition, improving its soil quality, since it partially remains at the end of that season. The amount of wheat straw left after the season (i.e., straw decomposition) depends on multiple factors (Jin et al., 2020). In this study, it was assumed that the residual percentage of straw is approximately 16% that will be stored in the soil in the long term (Fang et al., 2019) and a carbon content of straw of 49% of its dry matter (Brandão, 2012;IPCC, 2019).Theincreaseinthesoilcarboncontent was managed as an environmental credit in the results, assuming that the soil is absorbing the carbon. The remaining 84% of the carbon in the straw should be emitted. Nevertheless, this issue was not considered in the evaluation since no sequestration was considered either and both flows occur in the same year. The breakdown of straw in the following years was not considered for the same reason: it is balanced by carbon sequestration. 2.4.2. Direct and indirect field emissions An important issue in LCA applied to agricultural systems is the estimation of field emissions. Accordingly, field emissions due to the application of fertilizers and other agrochemicals were included in the assessment. N 2 O emissions were estimated according to the Intergovernmental Panel on Climate Change (IPCC, 2019). NO 2 and NH 3 emissions were calculated as proposed by the European Environmental Agency and European Monitoring and Evaluation Programme (EMEP/ EEA, 2019). NO 3 − leaching (Faist Emmenegger et al., 2009) and phosphate (PO 4 −3 ) leaching and runoff (Prasuhn, 2006) were also considered. Pesticides, fungicides and insecticides related emissions into air, water and soil were estimated according to PEFCR guidance (2017) and heavy metal emissions were not accounted for. Background information concerning procedure followed for the estimations and emission factors managed is detailed in the Supplementary Material (Section B and Table SM10 respectively). 2.5. Market value of products and by-products and production costs The crops included in the rotation systems yield more than one co-product with market price. This is the case of the commercial WWs (C-WW1-4) that yield WW grain (0.20€·kg −1 )andWW straw (0.07€·kg −1 ). In the case of potatoes, 10% of tuber yield does not meet food quality standards and is sold for animal feed. The price of potatoes for human consumption is 0.12–0.20 €·kg −1 (P1 and P2) and 0.25–0.30 €·kg −1 (P3). When sold for feed consumption, the price is 0.05 €·kg −1 . In the case of maize and oilseed rape, the straw is returned to the field (only partly in the case of maize); only maize silage (0.06 €·kg −1 for M1 and M2 and 0.09 €·kg −1 for M3) and oilseed (0.30 €·kg −1 for OSR1 and OSR2 and 0.40 €·kg −1 for OSR3) are obtained as main products. Regarding the native WWs (Gc-WW and Ge-WW), only grain is obtained as product. The straw is left in the soil as a nutrient supplier. The grain is sold at 0.40 €·kg −1 when it comes from conventional management (Gc-WW1-4) and at 0.48 €·kg −1 when it is from ecological management (Ge-WW1-4). When the straw is incorporated in the soil, it is not a co-product and there is no economic revenue (i.e., in GcWW1-4, Ge-WW1-4, M1-3 and OSR1-3). A summary of the amount Herbicide producon Inseccide producon Fungicide producon Seed producon Mineral ferlizer producon Diesel producon Machinery producon FIELD ESTABLISHMENT CROP GROWTH BIOMASS HARVESTING Foliarferlizer producon Organicferlizer Combuson emissions Agrochemical emissions -air emissions N2O, NO2, NH3 pescide, fungicide and herbicide derived emissions -water emissions NO3-, PO4-3 pescide, fungicide and herbicide derived emissions -soil emissions pescide, fungicide and herbicide derived emissions Agricultural product Agricultural by-product System boundaries Each crop in the rotaon Fig. 1. Main processes considered within the system boundary of each analysed crop with the rotation cropping systems under study. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 6 of co-products and yields per scenario, i.e. per rotation cycle, is shown in Table 1. Activity costs per agricultural operation (including diesel, machinery and personal costs) and input costs (e.g., agrochemicals, seeds and manure) are detailed for each individual crop in the Supplementary Material (Tables SM1–SM9). 2.6. Environmental assessment method Two impact assessment procedures were considered in the analysis. Firstly, the ReCiPe 2016 hierarchist Midpoint method V1.03 World (2010) (Huijbregts et al., 2017) was used for the selection of characterization factors required to estimate the environmental burdens and a set of impact categories at midpoint level commonly used in the environmental analysis of agricultural systems was considered for reporting the environmental profiles: global warming (GW), stratospheric ozone depletion (SOD); terrestrial acidification (TA), freshwater eutrophication (FE), marine eutrophication (ME), terrestrial ecotoxicity (TET), freshwater ecotoxicity (FET), marine ecotoxicity (MET) and fossil resource scarcity (FRS). The choice of these categories allowed the comparison with other related agricultural studies available in the literature. Secondly, the normalization factors from this method have been considered to establish a final ranking of cropping systems. This approach is contemporary, widely used and well recognized (Kalbar et al., 2016). The choice of this normalization approach is because having only one single adimensional score for the overall impacts can help disseminate the message to the audience better. The SimaPro software v9.0 (PRé Consultants, 2020) was used for the computational implementation of the life cycle inventories. 3. Environmental results and discussion The environmental profiles for each rotation system were reported in terms of nine impact categories. Firstly, crop rotations per hectare were analysed to answer the question focused on land management, which allowed for the identification of the crop rotations with the best andthe worst environmental profiles. Inaddition,a detailedassessment was conducted with the aim of identifying the activities or processes that contribute most to theseenvironmental burdens. Secondly, profiles were normalized per €of gross margin to give an answer to the financial question. 3.1. Environmental profile of the rotation cycles 3.1.1. General comparison Fig. 2 displays the comparative profile between the different crop rotations being studied in relation to the different impact categories. The comparison was performed in terms of hectare (ha). It is important to note that the consideration of this functional unit penalizes the crops with higher yields. For example, the commercial WW (crops C-WW1 and C-WW2) with maize (i.e. S2) is the scenario with the worst profile, as it reports the highest burdens in numerous impact categories. Similarly, S1, where the same WW variety is cultivated but in rotation with potato, should be the second worst cultivation option, reporting the worst scores in categories such as GW, TET and MET. The cultivation of this wheat variety requires multiple mechanized applications of mineral fertilizers (400 kg·ha −1 NPK and 200 kg·ha −1 CAN) and other agrochemicals (two herbicide applications and one fungicide dosage) compared to the native variety (see Tables SM1–SM3 in the Supplementary Material), which is one of the reasons behind these profiles. In addition, differences in the profiles of scenarios that include C-WW (S1-S3) are directly associated with the crop included as alternative in the rotation. As shown in Tables SM4–SM6 of the Supplementary Material, for potato, maize and oilseed rape under conventional management, the cultivation practices and thus, the degree of mechanization change considerably between them. Potato cropping requires a considerable level of mechanization and input use, with up to seven agrochemical applications (other than fertilizers) by means of an hydraulic sprayer connected to a tractor, two mineral fertilizations (800 kg·ha −1 NPK and 250 kg·ha −1 CAN), as well as numerous soil conditioning activities (mouldboard and chisel ploughing, and tillage). The number of agrochemical 2 applications is reduced in the case of maize and mainly for oilseed rape, where there is only one application of herbicide; the demand for mineral fertilizers is considerably reduced (350 kg·ha −1 NPK and 200 kg·ha −1 CAN) and fewer soil establishment activities are performed (only chisel ploughing and millingis combinedwithsowing). Thesedifferences justify the lowest environmental burdens per hectare for S3 (rotation with rapeseed) compared to S1 (rotation with potato) and S2 (rotation with maize). 2 From now, the term “agrochemicals”includes all applied chemicals, other than fertilizers. 0 10 20 30 40 50 60 70 80 90 100 GW SOD TA FE ME TET FET MET FRS )%(eliforpevitarapmoC S1 S2 S3 S4 S5 S6 S7 S8 S9 Fig. 2. Comparative profiles between the cycled rotation systems (S i ) per hectare. Acronyms: GW –Global Warming, SOD - Stratospheric Ozone Depletion, TA –Terrestrial Acidification, FE –Freshwater Eutrophication, ME –Marine Eutrophication, TET –Terrestrial Ecotoxicity, MET –Marine Ecotoxicity, FRS –Fossil Resource Scarcity. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 7 As for the S8, where the native WW variety (Ge-WW3) is combined with maize (M3) under the organic regime, this scenario reports the worst profile in terms of TA. The reason is associated with theuse of animal manure as fertilizer, mainly in maize crop. In this scenario, large amounts of manure are required (5 m 3 ·ha −1 of organic poultry manure in Ge-WW3 and, 8 t·ha −1 of ecological poultry manure and 15m 3 ·ha −1 of ecological cow manure in M3), whichimplies outstanding field emissions of ammonia into air (main hotspot in TA, 79% of total contributing emissions), among others. S7, where the autochthonous variety of WW is combined with potato(P3)reports the worse score in ME, mainly due to field emissions from manure use, specifically nitrate leaching. Crop rotations withoilseed rape (S3, S6 and S9) have thebestresults, in which the rotations with the native WW variety (S6 and S9) appear to be the most favourable in various impact categories (such as GW, TA FRS as well as toxicity and eutrophication related categories). In this sense, the cultivation of oilseed rape (OSR1, OSR2 and OSR3) requires fewer mechanical activities (and, therefore, less diesel), fertilizers and agrochemicalsthan maize and potato, resulting in lower environmental burdens. Among them, S9, where rapeseed (OSR3) is combined with the native wheat variety under ecological management (Ge-WW4) appears to be the best choice for land use, i.e. the cropping system that reports the lowest environmental burdens (in four of nine impacts analysed). Regardless the variety of WW cultivated in a rotation with potato (S1, S4 and S7), the cultivation of the latter is in general responsible for the highest environmental burdens from the rotation, i.e. it is responsible forthe largest contributionsto thedifferent impact categories, as detailed in Fig. 3, andespecially in thecategories relatedwith toxicity in S1 and S4. The reason for this result is associated with the extensive requirement of fertilizers and agrochemicals for the cultivation of potato under the non-organic regime. Nevertheless, even under organic management, the cultivation of potato plays a key role in the environmental profile of S7 since this crop demands more inputs and mechanized activities than winter wheat. In addition, and noting the profiles and contributions to the rotation, the WW grew after another previous WW crop (i.e., WW2 regardless of the management regime) reports a slight improvement in GW per hectare in comparison with the preceding one (i.e., WW1), due to the effect of the return of the straw to the field and the corresponding environmental benefits allocated to this issue (the effect from the increment in the soil organic carbon content due to the return of the straw to the field is assigned to the next crop, which implies an environmental credit). The profiles of the scenarios including maize (S2, S5 and S8) and oilseed rape (S3, S6 and S9) are dominated by the contributions from the cultivation of the alternate crops (see Figs. 4 and 5). The effect of maize is significant, as it is a crop with a high demand for agrochemicals (insecticides, fertilizers and fungicides) compared to WW. Therefore, its effect on toxicity-related impact categories TET, MET and TET is notable. The production of the required mineral fertilizers in maize produced under conventional management (S2 and S5) also plays a key role specifically in categories such as GW, OSD, TA, FE and FRS. The behaviour under organic regime (S8) undergoes a slight change mainly in the categories related to toxicity due to the use of organic fertilizers. Consequently, the effect of wheat cultivation on the rotation profile under ecological management is more noticeable in some impacts such as ME, FRS and toxicity related categories than in the other scenarios with maize. Concerning oilseed rape, the cultivation under conventional and organic regimes requires significant applications of fertilizers (mineral and organic) but low requirements for other agrochemicals. Thus, there are large emission rates of field emissions from fertilization, which penalizes their environmental profile in comparison with the corresponding wheat (in special in S6). Special attention should be given to the environmental credits identified in GW due to the return of straw to the field, which contributes to increase the carbon content of the soil. This effect is noticeable at S6 and S9 in the WW cultivation due to the reception of large amounts of rapeseed straw. 3.1.2. Contributing parameters to the environmental profiles The environmental profiles are determined, as displayed in Fig. 6,by field emissions and by the production of fertilizers (especially N-based 0 20 40 60 80 100 120 140 160 180 200 220 240 260 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 S1 S4 S7 GW *100 (kg CO2eq) SOD/500 (kg CFC11eq) TA (kg SO2eq) FE/25 (kg Peq) ME/5 (kg Neq) TET*500 (kg 1,4-DCB) FET*5 (kg 1,4-DCB) MET*10 (kg 1,4-DCB) FRS*25 (kg oil eq) ah·tinuqegk -1 3rd crop P 2nd crop WW 1st crop WW Fig. 3. Distribution of environmental profile of each rotation (6 years) per involved crops: winter wheat (WW) and potato (P). a) S1 –Scenario with commercial WW and conventional management; b) S4 –Scenario with autochthonous WW and conventional management; c) S7 –Scenario with autochthonous WW and ecological management. Acronyms: GW –Global Warming, SOD - Stratospheric Ozone Depletion, TA –Terrestrial Acidification, FE –Freshwater Eutrophication, ME –Marine Eutrophication, TET –Terrestrial Ecotoxicity, MET –Marine Ecotoxicity, FRS –Fossil Resource Scarcity. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 8 fertilizers). Regarding the latter, the effect of organic fertilizers in toxicity-related categories such as FET and MET, is less outstanding than that from mineral fertilizers. The production of the required agrochemicals (insecticides, pesticides and fungicides) has an unremarkable effect on the profile, regardless of the scenario under study. Mechanization activities are not very relevant, except in toxicityrelated categories and FRS due to diesel consumption and corresponding tail pipe emissions. Within the agricultural activities performed in the field, harvesting plays a key role –regardless of the crop - followed by mouldboard ploughing and soil tillage (all activities that require large amounts of diesel due to long hours of operation). When a baling operation is required as in S1-S3, the effect of this activity is also remarkable. Noting the contribution analysis depicted in Fig. 6,field emissions are the largest contributor to the environmental burdens (except in FRS). This contributing factor includes air, water and soil emissions derived from the application of fertilizers, agrochemicals and from the straw decomposition as well as the iLUC (289 kgCO 2 eq per system). Regarding these emissions, N 2 O derived from the application of nitrogen-based fertilizer (organic or inorganic) and straw is the most critical emission, specifically in GW and OSD. Concerning TA, attention should be paid to NH 3 and N 2 O emissions derived from N-fertilization. Consequently, the mechanized operations developed in the field were less important for these impact categories due to the low impact of tail-pipe emissions compared to those from fertilizer application. 0 20 40 60 80 100 120 140 160 180 200 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 S2 S5 S8 GW *100 (kg CO2eq) SOD/500 (kg CFC11eq) TA*2 (kg SO2eq) FE/25 (kg Peq) ME/5 (kg Neq) TET*500 (kg 1,4-DCB) FET*5 (kg 1,4-DCB) MET*10 (kg 1,4-DCB) FRS*25 (kg oil eq) ah·tinuqegk -1 2nd crop M 1st crop WW Fig. 4. Distribution of environmental profile of each rotation (6 years) per involved crops: winter wheat (WW) and maize (M). a) S2 –Scenario with commercial WW and conventional management; b) S5 –Scenario with autochthonous WW and conventional management; c) S8 –Scenario with autochthonous WW and ecological management. Acronyms: GW –Global Warming, SOD - Stratospheric Ozone Depletion, TA –Terrestrial Acidification, FE –Freshwater Eutrophication, ME –Marine Eutrophication, TET –Terrestrial Ecotoxicity, MET –Marine Ecotoxicity, FRS –Fossil Resource Scarcity. -20 0 20 40 60 80 100 120 140 160 180 200 220 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 S3 S6 S9 GW *100 (kg CO2eq) SOD/500 (kg CFC11eq) TA*2 (kg SO2eq) FE/25 (kg Peq) ME/5 (kg Neq) TET*500 (kg 1,4-DCB) FET*5 (kg 1,4-DCB) MET*10 (kg 1,4-DCB) FRS*25 (kg oil eq) ah·tinuqegk -1 2nd crop OSR 1st crop WW Fig. 5. Distribution of environmental profile of each rotation per involved crops: winter wheat (WW) and oilseed rape (OSR). a) S3 –Scenario with commercial WW and conventional management; b) S6 –Scenario with autochthonous WW and conventional management; c) S9 –Scenario with autochthonous WW and ecological management. Acronyms: GW – Global Warming, SOD - Stratospheric Ozone Depletion, TA –Terrestrial Acidification, FE –Freshwater Eutrophication, ME –Marine Eutrophication, TET –Terrestrial Ecotoxicity, MET – Marine Ecotoxicity, FRS –Fossil Resource Scarcity. S. González-García, F. Almeida, M.T. Moreira et al. Science of the Total Environment 770 (2021) 145270 9