Sustainable soil management measures: a synthesis of stakeholder recommendations

Soil degradation threatens agricultural production and soil multifunctionality. Efforts for private and public governance are increasingly emerging to leverage sustainable soil management. They require consensus across science, policy, and practice about what sustainable soil management entails. Such agreement does not yet exist to a sufficient extent in agronomic terms; what is lacking is a concise list of soil management measures that enjoy broad support among all stakeholders, and evidence on the question what hampers their implementation by farmers. We therefore screened stakeholder documents from public governance institutions, nongovernmental organizations, the agricultural industry, and conventional and organic farmer associations for recommendations related to agricultural soil management in Germany. Out of 46 recommended measures in total, we compiled a shortlist of the seven most consensual ones: (1) structural landscape elements, (2) organic fertilization, (3) diversified crop rotation, (4) permanent soil cover, (5) conservation tillage, (6) reduced soil loads, and (7) optimized timing of wheeling. Together, these measures support all agricultural soil functions, and address all major soil threats except soil contamination. Implementation barriers were identified with the aid of an online survey among farmers (n = 78). Results showed that a vast majority of farmers (> 80%) approved of all measures. Barriers were mostly considered to be economic and in some cases technological, while missing knowledge or other factors were less relevant. Barriers were stronger for those measures that cannot be implemented in isolation, but require a systemic diversification of the production system. This is especially the case for measures that are simultaneously beneficial to many soil functions (measures 2, 3, and 4). Results confirm the need for a diversification of the agricultural system in order to meet challenges of food security and climate change. The shortlist presents the first integrative compilation of sustainable soil management measures supporting the design of effective public or private governance.


Introduction
Agricultural soils are multifunctional. Beyond food production, they filter and store water, store and recycle nutrients, sequester carbon, and provide habitat for biological activity (Schulte et al. 2014). These functions play a crucial role in the resilience of agricultural production systems and agricultural landscape ecosystems. However, the ability of soils to perform these functions is threatened by degradation processes such as erosion, compaction, biodiversity decline, organic matter decline, or contamination (Glaesner et al. 2014). While the intensification of agriculture has strongly increased productivity, a concurrent rise in soil threats impairs the other soil functions (Techen and Helming 2017;Virto et al. 2015). Since soil fertility depends on the interplay of all functions, this also threatens long-term food security (Kibblewhite et al. 2008;Wagg et al. 2014). Historically, soil degradation resulting from poor soil management has led to the collapse of civilizations (Olson 1981;Snyder 2020). A sustainable management of agricultural soils that preserves or improves soil functions is therefore a pressing challenge, especially in light of a growing world population and climate change (Lal 2009).
There is increasing awareness among stakeholders of the importance of sustainable soil management. The United Nations (UN) declared 2015 as the International Year of Soils, researchers and institutional authorities highlight the importance of soils for the attainment of the UN's Sustainable Development Goals (EEA 2019; Helming et al. 2018;Keesstra et al. 2016), and recent popular documentaries raise public awareness about the need for soil protection (Tickell and Tickell 2020;Uhlig 2019).
However, at the European Union (EU) level, a legal framework specifically addressing soil protection is lacking (Virto et al. 2015). Although multiple EU regulations, such as the Common Agricultural Policy (CAP), the nitrates directive, the water framework directive, or the habitats directive address soil-related aspects, they do not specifically address the functioning of soils and do not account for the soil system in a holistic approach (Frelih-Larsen et al. 2017). Consequently, legislation pertaining to soil protection is inconsistent in the EU and insufficient for ensuring adequate protection of soils (Glaesner et al. 2014). By the end of 2021, the European Commission published a new Soil Strategy after a failed attempt toward a European Soil Framework Directive in 2014 (SIEUSOIL 2020). The new strategy foresees a soil health law by 2023. This is urgent, especially in view of the transnational magnitude and entanglement of challenges, such as climate change mitigation and adaptation or growing food demand, which threaten the achievement of the Sustainable Development Goals by 2030 (Ronchi et al. 2019;Ginzky et al. 2018).
Even in European countries where a national legal framework for soil protection has been in force for many years, such as in Germany, sufficient soil protection is not guaranteed. The German Soil Protection Act only partially prescribes preventive action, and the principles of good agricultural practices stated in the Act are considered too vague to be effective (Gunreben 2005;Prager et al. 2011;Rothstein et al. 2014). Consequently, soil degradation continues to be a serious problem in Germany and is expected to increase significantly by 2050 (Routschek et al. 2014;Wunder & Bodle 2019). Many stakeholders have become aware of this problem, and many recommendations for soil health-improving management measures in arable systems in Germany and Europe have been published (Fig. 1). They differ in terms of purpose, cost, systemic integration, and transformational requirements. They address different soil threats and soil functions, and their suitability varies regarding geophysical setting, soil properties, and farming system. However, there is still no consensus on what exactly sustainable soil management entails, and the multitude of different recommendations makes it difficult to see the forest for the trees. This hampers the adoption of soil governance measures, so that soil conservation management going beyond the legal requirements currently depends primarily on voluntary actions by farmers (Altobelli et al. 2020;FAO and ITPS 2015;Juerges and Hansjürgens 2018).
While agricultural soils are usually private property and their specific management is determined by farmers, management impacts on soil functions also affect public goods such as biodiversity, water regulation, and climate change mitigation (Powlson et al. 2011). Thus, there is a legitimate public interest in establishing mechanisms of public and private governance, such as regulations, subsidies, certification, and land-renting contracts, that promote sustainable soil management practices. To obtain a high degree of acceptance, which is particularly important in private governance, such mechanisms need to build on a consensus around sustainable soil management measures, which includes the perspectives and concerns of different stakeholder groups (Horschig et al. 2020).
Among the stakeholders, farmers are of central importance, as they are responsible for implementing measures and are directly affected by regulations pertaining to soil management. Although they have a vested interest in managing their soils sustainably, diverse obstacles and drivers for choosing unsustainable management options exist (European Commission 2006). Identifying such obstacles is important for designing governance mechanisms that efficiently incentivize sustainable soil management. Other relevant stakeholder groups are policy makers and public institutions, the agriculture and food industry, and environmental and social nongovernmental organizations (NGOs). To our knowledge, no work has yet been published that analyzes the views of these stakeholder groups toward agricultural measures required for sustainable soil management in a comprehensive way. To contribute to addressing this research gap, our objectives are to: i. give an overview of the recommendations for sustainable agricultural soil management from different stakeholder groups (longlist), ii. derive a shortlist of sustainable agricultural soil management measures that meet widespread agreement across all stakeholder groups, iii. analyze which soil threats and soil functions are affected by these management measures and identify possible gaps, and iv. analyze farmer perspectives on these measures and identify barriers to their implementation, including possible requirements for systemic change.
The results of our study provide a basis for designing public and private governance mechanisms. We use Germany as an example for a country in the temperate climate zone with highly industrialized agriculture and low yield gaps. We combine an analysis of stakeholder documents with a farmer survey.

Selection of stakeholders
A screening of stakeholders relevant to the German agricultural sector was performed, focusing on stakeholders active at the national or federal state level but also including relevant European and international institutions. Stakeholders were identified using a keyword-based Google search for documents addressing soil management, soil threats, or soil functions, and followed by a snowball sampling method (i.e., identification of one stakeholder could offer the connection to further stakeholders; cf. Atkinson and Flint 2004). All stakeholders were assigned to one of the following categories: • Public governance and institutions (GOV): ministries, environmental protection agencies, governmental advisory councils; institutions of the European Union and the United Nations; • Non-governmental organizations (NGO): interest groups with a focus on the environment, social issues, sustainability, or agricultural soils; • Agricultural industry (IND): companies and industry associations from the seeding, fertilizer, pesticide, and agricultural technology sectors; • Conventional farming associations (CONV): groups, networks, and associations of conventional farmers in Germany; • Organic farming associations (ORG): groups, networks, associations of organic farmers in Germany, and organic food labels.
We differentiated between conventional and organic farming associations due to different requirements and limitations applying to both farming systems (Crittenden et al. 2015). For GOV, well-known stakeholders such as international institutions and agricultural and environmental ministries of the German federal states were added. For the other categories, additional stakeholders were identified by searching for the German equivalents of the keywords "NGO" + "environment," "agriculture," or "arable" (NGO); for "agric*" + "seeding," "pesticide," "fertilizer," or "agricultural machinery" (IND); and for "agricultural association" or "farmers union" ± "organic" (CONV, ORG).

Selection of documents
Websites of the identified stakeholders were searched for soil-related documents using the keywords "soil," "soil protection," or the German equivalents. The following four criteria had to be met for a document to be selected: 1. Clear link to agricultural soil management in Germany, or valid globally. 2. Addresses specific management options directly applicable by farmers. Only listing desired outcomes, such as "avoid erosion" was not considered sufficient. 3. Applicable to arable cropping. 4. Specifically addresses soil protection, soil health improvement or sustainable soil management.

Analysis of documents
A full-text analysis was performed for all selected documents. For assessing the agricultural measures addressed, we developed an analytical framework (Fig. 2). The categorization of agricultural soil management measures was based on Techen and Helming (2017). However, we added "farming system" as a fifth main category and slightly modified the subcategories. Similar measures were combined under a common name. For example, "use of manure" and "use of compost" were recorded as "organic fertilizer." All measures were assigned to a subcategory, and linkages between the measures and soil threats or soil functions described in the documents were recorded. For each measure, we counted the total number of documents addressing it, as well as the number of documents per stakeholder group. Documents issued by multiple stakeholder groups were counted for the group with the largest number of contributing authors. There was one tie where a document had been issued by one stakeholder each from NGO and CONV. We assigned the document to CONV because this stakeholder group is closer to implementing the measures.
The overall share of documents recommending a measure reflects the agreement among the stakeholders. We created a shortlist of measures that were recommended by at least 1 3 of all stakeholder documents. This share also marks the threshold above which each measure was recommended by at least one stakeholder from each group.

Farmer survey
We conducted an online survey with German farmers using the open source application LimeSurvey® (version 4.3.15, build 200907, LimeSurvey GmbH, Hamburg, Germany). Although the survey was performed in German language, we refer here to English translations. In June/July 2021, an email with the link to the survey was sent to 16 major German agricultural organizations and 62 local farmer associations across all federal states, with a request to forward it to their members. All complete answers submitted by August 9, 2021, were included in the analysis (n = 78).
For all measures on the shortlist, we asked farmers the following questions: • Is the measure reasonable? • What is the most important challenge to implementation?
The responses to choose from included technology, economic constraints, lack of knowledge, and other (with a comment option).
If the comments provided with the option "other" specified technical/economic/knowledge-related barriers, then the answer was assigned to the respective category. All answer fields were mandatory (except for an open comment field at the very end of the survey). However, there was also the option to answer "I don't know/no answer." Inputs into the soil and farming system. Bars display the percentage of the 40 stakeholders that recommended the respective measure (2.5% = 1 stakeholder). Measures recommended by more than one-third of the stakeholders were included in the shortlist.

Sustainable soil management measures recommended by stakeholders
Out of the 85 stakeholders we identified, 40 issued documents that met our selection criteria (Appendix Table 1). The share within each group was 58% for GOV (14/24), 58% for NGO (7/12), 22% for IND (5/23), 33% for CONV (5/15), and 82% for ORG (9/11). Forty-six measures were identified in the document analysis (Fig. 3). Overall, "mechanical pressures" was the category most often addressed by the stakeholders, while "farming system" was the least addressed. The highest number of recommendations was recorded for "inputs into the soil." Of the groups, GOV stakeholders provided the highest number of recommendations.
Seven measures were recommended by more than onethird of the stakeholders and by stakeholders from all groups, namely, "structural landscape elements/biodiversity refuges," "permanent soil cover," "diversified crop rotation," "conservation tillage," "reduced soil loads," "optimized timing of wheeling," and "organic fertilizer" (Fig. 1). These measures formed our shortlist and are discussed further.
The largely differing numbers of documents per stakeholder group implied the risk of overrepresenting recommendations of groups with high numbers of documents (e.g., GOV). However, weighing the groups (i.e., calculating the arithmetic means (x̅ )  for each measure, based on equally weighted shares of agreement within each stakeholder group) caused only minimal changes in the long list and no changes in the shortlist.

Results of the farmer survey
Seventy-eight farmers replied to the survey. Respondents' locations were spread across Germany but mainly eastern states (the western federal states were poorly represented, possibly due to the severe floods in July 2021 that also affected agriculture (He et al. 2021)). Farm sizes were evenly distributed between farms smaller than 100 ha (36%), between 100 and 500 ha (38%) and larger than 500 ha (26%). Most respondents performed mixed arable and livestock farming (63%), while 27% performed only arable farming and 9% only livestock farming (other: 1%). The share of respondents performing organic farming was significantly higher (19%) than the German average (7.5%, cf. Destatis 2021). 78% performed conventional farming, and 3% performed both organic and conventional farming (Appendix Fig. 7) All measures on the shortlist were considered reasonable by a vast majority of the survey respondents (Fig. 4). There were some differences between organic and conventional farming systems for some measures: "structural landscape elements," "permanent soil cover," and "optimized timing of wheeling" were considered more reasonable by organic farmers than conventional farmers (93.3/77.0%, 100.0/78.7%, and 93.3/77.0%, respectively); "Conservation tillage" was considered more reasonable by conventional farmers than by organic farmers (91.8/73.3%). Economics was considered the most important challenge to implementation for five of the seven measures, while for "conservation tillage," it was technology, and for "optimized timing of wheeling," the responses were equally distributed and no prevalent barrier could be identified (Fig. 5).

Discussion of measures
In this section, the shortlisted measures are discussed. For each measure, we first report the benefits that the stakeholder documents associate with it, discuss benefits and challenges in the context of scientific literature, and address suitability and barriers of implementation from farmers' perspective. This also allows us to analyze how well the measures address soil threats and soil functions, and how easily they can be implemented in existing farming systems.

Structural landscape elements/biodiversity refuges
Structural elements in agricultural fields include hedgerows, live fences, shelterbelts, ponds, nonproductive trees, flower strips, buffer strips, perennial wooden structures, or stone or terrace walls. In the stakeholder documents, implementing structural elements was considered a measure that contributes mainly to the soils' habitat function and addresses the threat of biodiversity decline, while it was often not clear from the documents whether this refers exclusively to soil organisms or also to aboveground biodiversity. Many documents also pointed to a link with the production function of soils because biodiversity is a functional element of soil fertility and because structural elements may provide shelter for pollinators and other beneficial species. Structural elements were also frequently linked to the prevention of wind and water erosion, as well as to preventing organic matter decline. To a lesser extent, positive effects of structural elements on water purification and retention and carbon sequestration were mentioned.
Research confirms that structural elements form important soil biodiversity reservoirs (Barthel et al. 2013) and are crucial for habitat connectivity and for the preservation of species that are incompatible with agriculture (Grass et al. 2019;Savić et al. 2021). They provide shelter for pollinators and predators and enhance their diversity and abundance (Dainese et al. 2017;van Vooren et al. 2017). The positive effect on predators may also reduce pesticide demand (Steingröver et al. 2010;Bianchi et al. 2008). Linear elements such as hedgerows, or flower strips can reduce soil erosion (Marshall and Moonen 2002), contribute to soil sediment and nutrient interception (Garratt et al. 2017), and thus benefit water quality (Tamburini et al. 2020). They can also significantly increase organic matter content and carbon stock in adjacent fields (van Vooren et al. 2017;Wojewoda and Russel 2003). Structural landscape elements are important for the intrinsic and functional diversity of agricultural landscapes (van den Berge et al. Grass et al. 2019) and therefore contribute directly and indirectly to soil multifunctionality.
While crop yield has been found to be more stable and more resilient to extreme events on fields with structural elements (Redhead et al. 2020), the overall yield is significantly reduced in close proximity to hedgerows and only slightly increased at farther distances (Raatz et al. 2019;van Vooren et al. 2017). Additionally, structural landscape elements occupy agricultural land, resulting in a trade-off between ecosystem service delivery and crop yield (van Vooren et al. 2017;Redhead et al. 2020). While seminatural habitats provide better pollination in agricultural fields, this cannot counterbalance the higher costs due to increased working time and fuel consumption Kirchweger et al. 2020).
Accordingly, while 81% of the survey respondents deemed the implementation and preservation of structural landscape elements reasonable, economic constraints were perceived as the most important obstacle to their implementation (58%). Comments displayed a rather low motivation 1 3 of farmers to implement and preserve structural elements and highlighted opportunity costs due to the occupied area and increased workload resulting from maintenance tasks. This might be especially relevant for small farms where taking land out of cultivation is more challenging than on larger farms (Wuepper et al. 2020). Several respondents commented that implementing structural landscape elements would only be possible with increased funding, while the application process for existing funding was perceived as complicated. In Europe, implementing landscape elements can be funded if they are registered as Ecological Focus Areas (EFA). However, due to strict requirements (e.g., regarding spatial dimensions) and a difficult administrative registration process, most farmers do not avail of this option (Zinngrebe et al. 2017).
Thus, improved funding schemes for structural elements may improve the adoption of this measure. It could easily be integrated into existing farming schemes, requiring only slight changes to management, such as respecting protective distances to structural elements when applying pesticides and fertilizers. Improved knowledge transfer about the longterm beneficial effects of diversely structured landscapes for yield stability and resilience might also foster a more positive attitude of farmers toward structural elements.

Organic fertilizer
This measure refers to an increased use of organic fertilizer or the addition of organic amendments. This includes the incorporation of straw and other crop residues, green manure, farmyard manure, solid dung, compost, sewage sludge, fermentation residues, horn manure and horn silica, or biochar. While some stakeholders recommended using mineral fertilizer as an additional option, others recommended completely avoiding mineral fertilizers. Several documents contained specifications, e.g., that the addition of organic amendments should be done in a balanced and context-adapted way, that knowledge about the nutrient composition of the organic amendments was required, or that the organic material should be incorporated into the soil (especially slurry). This measure was mostly linked to nutrient supply, humus preservation and formation, soil structure, and soil fertility. Organic fertilizers were considered to contribute to the improvement and maintenance of soil health, enabling good crop performance. Further linkages were made to the habitat function of soils, soil water holding capacity, erosion prevention, pest control, and the closing of nutrient cycles.
The use of organic fertilizer/adding diverse organic amendments to the soil has beneficial effects on soils, including improved biological functions, increased organic carbon, improved soil aggregate stability, more balanced release of N fertilizers, decreased nitrate leaching, pest and pathogen suppression, and improved crop yields; especially when regularly applied over long periods (Bailey and Lazarovits 2003;Crystal-Ornelas et al. 2021;Diacono and Montemurro 2011;Vida et al. 2020). However, the financial profitability of organic inputs is uncertain, especially in the short term Hijbeek et al. 2019), while excessive use of organic fertilizers is associated with nitrate leaching and groundwater pollution (Kühling et al. 2021). Furthermore, the regional concentration of specialized crop farms and livestock farms may cause shortages in the availability of animal manure, as transporting manure over long distances is economically unviable (Biberacher et al. 2009;Wezel et al. 2014) and results in high labor and energy costs (Sanchez et al. 2004). Another obstacle is the varying nutrient content of organic fertilizers which may lead farmers to opt for mineral fertilizer instead (Bert et al. 2009;Biberacher et al. 2009). Additionally, farmers also often lack knowledge of and experience with biobased fertilizers, e.g., regarding the timing of N availability to meet crop demands (Tur-Cardona et al. 2018;Sanchez et al. 2004). Tur-Cardona et al. (2018) found that farmers are more likely to choose organic fertilizers when they are clearly cheaper than mineral fertilizers. With the drastic increase of the energy prices since early 2022, organic fertilizers may become more attractive to farmers. However, solid forms of fertilizers and fertilizers that ensure a fast release of nutrients are typically preferred by farmers. While unprocessed manure is mostly cost-free for them, processed organic fertilizers (e.g., digestates) come in a more convenient form (e.g., pellets, less odorous) and without uncertainties regarding their nutrient content (Case et al. 2017;Tur-Cardona et al. 2018). However, heavily processed organic fertilizers may have reduced to no beneficial effects on soils as compared to mineral fertilizers (Löbmann et al. 2016).
Preferring organic over mineral fertilizer was deemed reasonable by 92% of the respondents, with no difference between conventional and organic farmers, but with a small difference between farms with livestock (96%) and farms without livestock (88%). Thirty-six percent of respondents considered economic constraints to be the most important obstacle to implementing this measure. In the comments, respondents pointed out decreasing livestock numbers in some regions, the low economic value of slurry as opposed to high costs, the effort needed for transportation and application, and high costs for machinery (trailing shoe, slurry injection). Legal requirements, such as the ban on spreading slurry on frozen soil and the amended German Fertilizer Ordinance in general were named as additional obstacles.
The expected positive effect on soil quality and associated co-benefits may function as a driver for implementations of this measure. The decision to increase organic fertilizer use may motivate specialized crop farms to switch to a mixed system that includes livestock, resulting in a complete redesign of the farming system (Wezel et al. 2014). More research is needed, e.g., on the linkage between organic input and pests, diseases, and weeds (Hijbeek et al. 2019), to reduce farmer uncertainty regarding the effects of organic amendments.

Diversified crop rotation
The level of specification for this measure differed between documents. Specific recommendations were to alternate leafy and cereal crops, winter and summer crops, and humus-decreasing and humus-enhancing crops; integrate catch crops, legumes, and deep-rooting crops; not grow corn directly after corn; and integrate rotational fallow land, rotational grazing, or planted set-aside areas for soil regeneration. More general recommendations were to establish crop rotations with at least 3 to 5 elements and pay attention to crop-specific cultivation pauses (NGO). Multiple benefits were associated with diversified crop rotations, such as increased biodiversity in agricultural landscapes and a reduction in pest pressure. This would reduce pesticide use and the associated risks of soil contamination and lead to more resilient crops. Furthermore, this measure was often linked to erosion control. Finally, diversified rotations also come with diversified root systems. This was considered to improve soil structure, increase fertility, reduce the risk of compaction and contribute to carbon sequestration and soil organic matter preservation.
Many studies confirm the positive effects of diverse crop rotations on soil biodiversity, microbial activity, soil structure, and aggregation, and consequently, on long-term fertility, habitat quality, erosion risk mitigation, and water retention (Ayalew et al. 2021;D'Acunto et al. 2018;Kay 1990;Kollas et al. 2015;Munkholm et al. 2013;Tiemann et al. 2015). However, effects depend on the specific management. For example, increases in carbon sequestration depend on crop choices, site-specific factors, and management (FAO and ITPS 2021; Scheffler and Wiegmann 2019). For beneficial effects on soil microbial communities and reduced pesticide use, rotations of 5 or more crops, including different crops and cultivation types such as winter and summer cereals, roots and tubers, legumes, or set-aside, have been recommended (Andert et al. 2016;Tiemann et al. 2015). In Europe, farms must already practice some degree of crop diversification to receive CAP greening payments; on the farm level, farms of a size between 10 and 30 ha need to grow at least 2 different crops, and farms larger than 30 ha need to grow at least 3 different crops, whereby the main crop must not cover more than 75% of the area (EC 2021). Accordingly, the majority of farms in Germany grow only 2 or 3 different crops at a time. Rotations are dominated by large proportions of maize and wheat, and little consideration is given to phytosanitary aspects (suitable precrop, cultivation pauses) (BMEL 2019; Steinmann and Dobers 2013).
Almost all survey respondents (96%) thought it was reasonable to diversify crop rotations. Farmers are aware of the ecological advantages of a more diverse crop rotation (Andert et al. 2016). However, their options are restricted by farm specialization, the availability of machinery on the farm, knowledge, market preferences, agricultural policies, and soil conditions. This results in (regional) preferences for specific crops (FAO and ITPS 2021;Steinmann and Dobers 2013). A majority of respondents (63%) considered economic constraints the most important obstacle to implementing this measure, followed by a lack of knowledge (21%). The comments revealed that farm type and size are also restricting factors: respondents stated that for small farms or farms growing fodder crops, there was little scope for diversifying crop rotations. Further obstacles were seen in uncertainties about revenues and yield stability for some crops.
Overall, implementing more diversified crop rotations would require substantial systemic changes for most farms in Germany. To motivate the implementation of this measure by German farmers, Andert et al. (2016) recommend providing more detailed information on the advantages of crop diversity, as well as a better design of financial and political incentives, rather than using command and control measures.

Permanent soil cover
Stakeholders recommended keeping soils covered as much as possible throughout the year. This can be achieved through catch crops, undersown crops, mulching (e.g., with crop residues), and optimization of the crop rotation (minimizing the time between harvest and sowing of the succeeding crop). More specific recommendations for catch crops were the use of seed mixtures and optimized seeding time to minimize the risk of crop failure due to pests, diseases, or weather extremes (e.g., dry periods). Furthermore, avoiding row crops (e.g., substituting corn with alfalfa or clover grass in biogas production) or performing mulch sowing for row crops, as well as perennial crops or dense sowing (e.g., choosing more dense cereals over winter wheat), was recommended. Possible economic disadvantages were mentioned for some of these management options, but also the possibility of reduced herbicide demand due to the weed suppressing function of soil cover. Continuous soil cover was mostly linked to the prevention of erosion. Furthermore, the increased organic matter input caused by this measure was considered to contribute to carbon sequestration and the prevention of soil organic matter decline, with positive effects on soil fertility and yield stability. Finally, this measure was associated with biodiversity preservation and an improved habitat function for above and belowground organisms.
Soil cover is a key factor in reducing the risk of wind and water erosion (Deumlich et al. 2006). In the universal soil loss equation (USLE), soil cover management is represented by the C-factor, which is the only factor that farmers can control (Auerswald et al. 2021). Cover crops are particularly favorable, since they provide soil cover during winter when soils would otherwise be barren. However, they come with additional costs for farmers (e.g., seeds, additional management) and their implementation may require changes to the established crop rotations (Sattler & Nagel 2010). In this regard, farmers may lack specific knowledge (Werner et al. 2017). Furthermore, continuous vegetation cover increases the overall water demand and reduces groundwater recharge (Lischeid and Natkhin 2011). Nonetheless, cover crops are among the most commonly applied EFA options in Europe (Zinngrebe et al. 2017), indicating a fair level of acceptance and practicability. Cover crops suppress weeds and thus reduce the need for tillage or herbicides (Brust et al. 2014;Gerhards & Schappert 2020). Furthermore, they increase the soil organic matter content (Poeplau & Don 2015), help recycle nitrogen in the upper soil layer (Hooker et al. 2008), improve soil structure and soil hydraulic properties, and have a beneficial effect on the habitat function of soils (Gerhards & Schappert 2020). The use of regional species and seed mixtures may result in more efficient soil cover, due to their adaptation to local conditions and a higher species diversity (Dybzinski et al. 2008;Nabel et al. 2021). Efficient soil cover can also be achieved by undersown crops (i.e., sowing a cover crop into the main crop after its establishment), while yields may be unaffected or even increase (Bergkvist et al. 2011;Johnson et al. 2021). Providing soil cover through mulching with crop residues (e.g., wheat straw) is a common practice in conservation tillage systems. Depending on the quantity and quality of residues, mulching can increase soil fertility, reduce fertilizer need, increase soil organic matter, and contribute to sustaining stable soil ecosystems (Kollas et al. 2015;Tiemann et al. 2015). However, mulching may also add to the persistence of residue-borne pathogens (Koivunen et al. 2018). This problem is likely to worsen with ongoing climate change (Fareed Mohamed Wahdan et al. 2020).
Maintaining soil cover was deemed reasonable by 83% of the respondents. Economic constraints (32%) and lack of knowledge (28%) were perceived as the most important obstacles to implementation. In the comments, farmers pointed to problems of water scarcity, phytosanitary problems, the planned ban on glyphosate in the EU, the need for appropriate machinery, and the incompatibility of this measure with specific crops.
Improved information for farmers on how to achieve continuous soil cover, distributed through, e.g., farm advisory systems, could address specific knowledge deficits and increase the adoption of this measure (Werner et al. 2017). However, implementing the different soil cover management options also requires systemic change. For cover crops, rotations may need to be adapted, while for the integration of undersown crops, compatible crops must be selected and specialized machinery, such as for combined harvesting and sowing, may be required (Sattler and Nagel 2010). Where water is a limiting factor, mulching may be preferable to continuous vegetation cover. In this case, diversified crop rotations may be necessary to avoid increased pest pressure (Buhre et al. 2009). Alternatively, farmers may consider switching to conservation tillage systems, as described in the following section.

Conservation tillage
Conservation tillage practices refer to management where mulch seeding, strip-till, or direct seeding replace conventional plowing to minimize mechanical disturbances of the soil. These practices were considered to improve the soils' carrying capacity; increase carbon sequestration; lower water losses; increase biological activity; prevent erosion, compaction, and capping; and reduce NO 3 losses. Opinions differed on how to manage the increased weed pressure associated with plowless systems. NGO and GOV stakeholders stated that farmers should not use broad-spectrum herbicides, or at least should not increase their herbicide use. Instead, the establishment of diverse plant communities and adapted crop rotations were suggested for countering weed pressure. In contrast, CONV, IND, and other GOV stakeholders considered conservation tillage practices to be inevitably linked with broadspectrum herbicide use, especially where a high degree of soil cover is maintained.
Conservation tillage measures can increase soil carrying capacity and reduce soil compaction, though effects differ depending on soil properties and types of management (Mirzavand and Moradi-Talebbeigi 2021; Pöhlitz et al. 2018). On the other hand, switching from conventional tillage to conservation tillage may also increase compaction, e.g., when crop rotations do not include deep-rooting crops and when the conditions for bioturbation by earthworms are unfavorable . Furthermore, heavy machinery can cause higher compaction in fields under conservation tillage than in plowed fields (Koch et al. 2008). Accordingly, Peigné et al. (2018) found that after 10 years of conservation tillage in an organic farming system on a sandy soil, soil compaction had increased, possibly due to intensive mechanical weed control measures. While it is widely acknowledged that conservation tillage enhances soil organic carbon (SOC) content in the upper soil layer, it is controversial whether this contributes to climate change mitigation, as the soil carbon stock in deeper soil layers can decrease (Lou et al. 2012;Moreno et al. 2006). For the whole soil profile, Dimassi et al. (2014) report a net decrease in the soil organic carbon stock in reduced tillage systems under wet and warm conditions. Even where an increase in carbon stock is achieved, the climate benefits may be offset by higher N 2 O emissions (Guenet et al. 2021;Mei et al. 2018). Conservation tillage practices have also been found to reduce soil erosion (Seitz et al. 2018). Obstacles to implementation mostly arise from trade-offs with weed pressure. As mechanical weed control through plowing is no longer applied, conservation tillage practices typically result in increased herbicide use and the combination of conservation tillage and use of broad-spectrum herbicides reduces labor requirements and working costs (Mal et al. 2015), while effects on soil biodiversity can be positive or negative for different invertebrate, microbial, and fungal taxa (Chávez-Ortiz et al. 2022;Froslev et al. 2022;van Capelle et al. 2012;Zaller et al. 2014). A trade-off with productivity may arise because it usually takes longer for untilled soils to warm up in spring, resulting in later crop growth and reduced mineralization (BLE 2020). The effects of conservation tillage cannot be generalized as they strongly depend on soil properties, climatic conditions, and farm management, such as the type of conservation tillage, cultivated crop, and weed management. Accordingly, the main influencing factors for adoption among European farmers are the biophysical conditions of an area and agricultural specialization (especially the cultivated crop), while the timing of sowing and harvest, as well as the socioeconomic conditions of the area, also plays a role (Bijttebier et al. 2018).
In the farmer survey, 88% of respondents considered conservation tillage a reasonable option, while 6% did not. Technology was considered the main obstacle to implementation (45%), followed by economic constraints (15%). For other reasons, farmers pointed to the planned ban on glyphosate use in Europe, which would limit the availability of broad-spectrum herbicides. Direct seeding was especially considered to depend on the application of these herbicides, although many farmers were aware of negative impacts on the environment. Where farmers cannot use broad-spectrum herbicides, as in organic farming systems, conservation tillage practices are difficult. Accordingly, among the organic farmers, a higher share (18%) rejected the measure.
Conservation tillage practices require specialized machinery and potentially different timing of farming operations, but they can easily be implemented without major systemic changes if broad-spectrum herbicides are used for weed control. For increased herbicide use to be avoided, successful application of conservation tillage requires a high standard of management, including thorough crop choice and rotations tailored to local soil and climatic conditions (Peigné et al. 2007), indicating substantial systemic change. Nabel et al. (2021) suggest that the use of broad-spectrum herbicides can be avoided in mulch seeding and that tillage could be used as a measure for pest control if all other options fail. In this case, they recommend immediately applying organic amendments to offset the carbon losses caused by the tillage and allow for a quick fauna restoration.

Reduced soil loads
A reduction in soil loads was recommended by 19 stakeholders (47.5%). Recommendations were (a) to reduce machinery weight, e.g., by using information and communication technology (ICT) and robotics (also to detect soil compaction), filling bunkers of harvesting machinery only partly, or performing umbilical slurry spreading where the slurry is pumped from the field edge to the tractor via a flexible pipeline, and (b) to ensure a larger contact area and better weight distribution, e.g., by using tire pressure regulation, twin tires, high floatation tires, caterpillar machinery, additional axles, crab-steering (offset track driving), or semimounted or attached devices. Unloading/transfer technology (conveyor belts) and the separation of field and street transport were recommended to facilitate optimal tire pressure for both purposes. Ideally, soil-protective properties should already be taken into account when purchasing machinery. A combination of multiple management options was considered to be most effective. The main benefit was considered to be the prevention of soil compaction, and only a few linkages to soil functions or other soil threats were described. Good soil structure, high earthworm activity, and avoided costs for potential soil loosening were mentioned as potential co-benefits of reduced weight pressure, while low tire pressure was considered to improve traction and thus reduce fuel costs and working time.
Many studies recommend the use of lighter machinery and an increase in the size of the contact area (Frelih-Larsen et al. 2018;Ledermüller et al. 2018;ten Damme et al. 2019), as well as low tire pressure (Brunotte and Lorenz 2015;ten Damme et al. 2019). The use of lightweight agricultural robots is still uncommon in Germany. Although some multifunctional models exist and are considered promising technologies (BMEL 2021;Scholz et al. 2014), farmers are generally skeptical about return on investment (Barnes et al. 2019). Findings by Rübcke von Veltheim and Heise (2020; indicate that the willingness of farmers to adopt robotics correlates with field size rather than with farm size. Reducing soil loads to prevent subsoil compaction is crucial, as the impacts of compaction are not immediately visible (Frelih-Larsen et al. 2018), and compaction can persist for decades or centuries (Berisso et al. 2012;Sharratt et al. 1998). Only in some cases can soils alleviate compaction quickly without human intervention (Badalíková, 2010). Prevention is also less costly than dealing with the consequences of subsoil compaction, such as decreased water infiltration, increased erosion risk, and decreased crop 1 3 performance and farm profitability Jamali et al. 2021).
Since both the weight pressure and frequency of wheeling are factors influencing soil compaction, the use of lighter machinery may not be beneficial if it leads to more frequent wheeling (Seehusen et al. 2019). For better weight distribution, twin tires are useful, but they add to the width of the vehicle. If this exceeds the maximum allowed on public streets, tires need to be mounted and dismounted at the field, which is costly and time consuming (KTBL 2011). Similarly, there is a weight limit for caterpillar machinery on German roads. Attached devices also improve weight distribution but require a larger area for turning maneuvers, making this measure only practicable on large fields. Field enlargement, however, is undesirable from the perspective of sustainable management. Additional axles are another option, although the alleviating effect on soil pressure is negated where manufacturers implement them to enable higher total machine weights . Low tire pressure is beneficial in the field but not feasible for street travel. Regulation systems can be used to adjust the pressure (Volk et al. 2011), although they are still expensive. Furthermore, while lowering the pressure is easy, increasing it requires time and energy, especially when high loads are carried (e.g., after harvest). Pressure regulation is therefore easier for slurry application, where the trailer is lighter when returning from the field, than for harvesting machinery (KTBL 2011). Finally, workers need to be trained and instructed on pressure regulation. Where management steps are executed by external contractors, the farmer's influence on this is limited (KTBL 2011).
In the farmer survey, 96% of respondents deemed a reduction in the weight pressure reasonable (not reasonable: 4%). Obstacles to implementation were considered to be mainly economic constraints (49%) or related to technology (29%). Switching from large machinery to lighter alternatives has economic consequences as it requires investment and may decrease cost and working time efficiency. Survey respondents stated that the high costs for specialized machinery would require the use of large areas to be profitable and pose a problem for smaller farms. Thorsøe et al. (2019) discourage a general weight limit for machinery because it would unnecessarily restrict farmer options at times when the soil is dry and able to carry high loads. The proposed management options for this measure are mostly technical, requiring little systemic change but typically investment in specialized machinery. In this regard, the measure of "filling harvesting bunkers only partly" is an exception as new machinery is not required. However, it is time consuming due to more frequent unloading and therefore costly.

Optimized timing of wheeling
A total of 18 stakeholders (45%) recommended optimized timing of wheeling, meaning that field traffic should be avoided when the soil is too wet to prevent compaction and maintain a good soil structure. For this purpose, it was recommended that soil consistency/soil humidity be measured and machinery and working capacities be reserved to be able to perform agronomic operations only at suitable times. Some stakeholders recommended combining this measure with other management options for optimal compaction prevention, e.g., conservation tillage for better soil carrying capacity, the use of wide tires, and the use of the crab-steering (offset track driving) mode. Others pointed out the importance of this measure for compaction prevention.
Several studies highlight the importance of this measure for preventing subsoil compaction van den Akker and Soane 2005). Since the carrying capacity of soil is strongly influenced by soil moisture, there is a risk of compaction when soils are wet. The weight pressure of machinery may then exceed the soil's carrying capacity, especially for management tasks characterized by high soil loads, such as slurry distribution or harvest (Thorsøe et al. 2019). Preventing compaction can also reduce the risk of water erosion (Fullen 1985). However, tight work schedules may force farmers to use machinery under unfavorable soil moisture conditions, as specialized machinery needs a high degree of utilization to be profitable (Lorenz et al. 2016). Further barriers to sustainably addressing subsoil compaction are a lack of knowledge and problem awareness, the preference of farmers to fulfill short-term contracts over long-term soil fertility management, outsourcing of responsibilities (e.g., farming operations done by contractors), and the complex nature of subsoil compaction (Thorsøe et al. 2019). Marx and Jacobs (2020) also note that the collaboration between scientists and practitioners is still insufficient; furthermore, farmers experience top-down communication of recommendations for compaction prevention that are often generalizing or difficult to understand, which limits the acceptance of recommended measures.
Eighty-one percent of the survey respondents rated the optimization of the wheeling timing as reasonable, while 13% did not. Responses related to the main obstacles to implementation were evenly distributed among knowledge (26%), economic constraints (23%), and technology (22%). Farmers commented that (unpredictable) weather conditions complicate the implementation of this measure. Further problems were seen in the time requirements and organizational challenges, such as outsourcing operations to contractors, or when farming was practiced as a secondary job, which would sometimes make it impossible to take soil conditions into account. Reserving or increasing working capacities was commented to be unrealistic for economic reasons.
To promote the implementation of this measure, Thorsøe et al. (2019) recommend the development of a legal framework that incentivizes and enables sustainable management decisions. They stress the need for systemic solutions that include not only farmers but also other stakeholders such as farming education institutions, machinery manufacturers, contractors and retailers. Technical solutions are also under development. These include decision-support tools and concepts that define the timeframe for the workability of the soil, considering the weather, compaction risk, and machine utilization (Edwards et al. 2016;Ledermüller et al. 2018;Lorenz et al. 2016;Obour et al. 2017). They could help optimize the timing of wheeling as much as possible, without requiring a substantial systemic change for farms. However, for regions where seasonal high soil moisture levels regularly occur, Chamen et al. (2003) recommend rather choosing crops that require little work during this time, which implies greater changes for farms.

Synthesis of measures
Our analysis of the effects, co-benefits, and trade-offs of the proposed management measures shows that benefits for soil functions and reductions in soil threats are highly interlinked. Most of the proposed measures improve multiple soil functions simultaneously, and many of the soil threats and functions are addressed by multiple measures (Fig. 6). Erosion and water purification and retention are addressed by all seven measures. Compaction, biodiversity and organic matter/carbon sequestration are addressed by five to six of the seven measures. The production function was not affected negatively by any of the shortlisted measures. However, economic trade-offs may exist since many of the measures may be less profitable. For example, diversified crop rotations may require more costly seeds and the cultivation of less profitable crops, or land area for production may be reduced if structural landscape elements are established or if green manure is cultivated for organic fertilizers. Soil contamination was the only soil threat that was not addressed by the shortlist of measures. Conversely, some organic fertilizers bear the potential to contribute to the contamination of soils, e.g., through heavy metals in recycled sewage sludge (Tarpani et al. 2020).
While reducing soil loads and optimizing the timing of wheeling are suitable options for preventing soil compaction, these measures do not provide many other benefits to agricultural soils, indicating that technological solutions alone are not sufficient for sustainable soil management. On the other hand, the measures that have multiple beneficial effects on soils, namely, "organic fertilization," "diversified crop rotation," and "permanent soil cover," are also the measures that will involve the greatest systemic changes in the farming system. Organic fertilization requires growing green manure and/or developing ways to obtain animal-based organic fertilizers, i.e., introducing livestock into the farm system or at least establishing a collaboration with livestock farms. Diversifying crop rotations and maintaining continuous soil cover require adaptations of crop rotations and workflows and will affect farm revenues. These examples support the general finding about the importance of diversification for the improvement of ecosystem services in agricultural systems (Tamburini et al. 2020). In the long term, for "structural landscape elements," "organic fertilization," "diversified crop rotation," and "permanent soil cover," a positive impact on the production function is even possible. The soil function "recycling of nutrients" is only supported by "organic fertilization" and "diversified crop rotation." This highlights the importance of these two measures, especially for achieving closed nutrient cycles, which is considered a crucial element of sustainable agriculture but at the same time linked to major systemic changes not only at the farm level, but also for the entire agrifood system (Magdoff et al. 1997).

Methodology discussion
The objectives of this study required several simplifications. All stakeholder documents meeting our selection criteria were treated equally, irrespective of differences in quality, level of detail, or influence of the respective stakeholders. Furthermore, the categorization of stakeholder groups did not account for within-group heterogeneities. Finally, the bundling of recommendations under a common term always implies a loss of information. However, these simplifications allowed the recommendations to be sorted, overlaps between stakeholder opinions to be identified, and widely accepted management measures to be derived.
It is possible that the keyword-based search did not identify all relevant documents. The number of documents found differed greatly between stakeholder groups, which may reflect differences in the awareness of the need for more sustainable soil management, a group's role with regard to promoting or implementing such management, or specific biases and interests. Overall, the number of documents per group was considered too low to allow for a detailed analysis of within-group and between-group differences.

Conclusion
Governance for more sustainable soil management is easiest to implement and most effective where proposed measures meet with approval across a wide set of stakeholder groups. Out of the multitude of measures recommended by stakeholders, we derived a shortlist of seven measures for which there is a high degree of agreement, and which are proposed by stakeholders from all investigated stakeholder groups. The measures address all soil functions and all soil threats except for contamination. For this soil threat, additional measures will be necessary.
Many of the measures address more than one threat or function, and most of the measures have multiple benefits. However, the measures require varying degrees of systemic change in the farm system to be implemented, even more so since the measures should ideally be implemented in combination. Diversification is one of the key principles behind more sustainable soil management. Our findings support the common evidence that a diversification of approaches and cropping systems is the preferable way to maintain and restore soil health and to meet future challenges of food security and climate change.
In our survey, the vast majority of farmers supported the shortlist of measures. Obstacles to implementation were mainly considered to be economic constraints and partly technical, while a lack of knowledge was seen as only a minor obstacle. These results provide valuable information for the formulation of effective governance options.
While this work was able to identify agricultural measures with wide support across all stakeholder groups, the definition of these measures is still too broad for direct implementation in a farming or policy context. Future research should seek to specify these measures and tailor them to varying local conditions and farming contexts.  (2) Uncover the fraudulent labeling: glyphosate is neither soil protective nor climate protective (3) Soil protection in agriculture

Statistical survey data
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