Contents

1 Introduction

The sustainable management of agricultural soils is a global concern. Soils are the basis for producing the greatest quantity of food and feed and contribute an increasing share of biomass for energetic and industrial purposes. Agricultural soils also fulfill fundamental functions for ecosystem services, such as water and nutrient regulation and carbon storage, and they contribute essentially to biodiversity. But at the same time, soil functions are threatened by degradation processes, and approximately one quarter of global cropland may already be degrading due to human pressures (Le et al. 2016).

While intensive agriculture is generally associated with promoting soil degradation, the reality is more complex (FAO and ITPS 2015). The occurrence and rate of soil degradation depend on the combination of soil management decisions and their interrelations with local geo-biophysical, socio-economic, and climatic conditions. The terms “sustainable intensification” (Garnett et al. 2013) and “ecological intensification” (Tittonell 2014) initiated the challenge for agricultural management to increase the production while minimizing the resource use, intensifying ecological interaction, exploiting the inherent capacity of the soils to produce, and maintaining all other soil functions and ecosystem services. This indicates that the multifunctionality of soils (Schulte et al. 2014) must be managed and improved.

Taking appropriate actions for sustainable intensification requires the analysis of drivers of soil management and the challenges and opportunities they entail. This is especially true for research; being an important driver, it has the potential to reinforce positive and mitigate negative developments regarding soil management. As research often takes many years before the results may become applicable in the field (Colinet et al. 2014, similar Alston et al. 2008), foresight on the drivers of soil management is important to inform research directions.

For Europe, a number of foresight studies on agriculture exist. Important examples include Last et al. (2015) with a foresight study on the Swiss food system, Teagasc (2016) on the Irish agri-food sector, and Foresight (2011) and Alexandratos and Bruinsma (2012) on the future of food and farming on a global scale. Schindler et al. (2014) and EU SCAR (2016) addressed information and communication technologies (ICT) and robotics in European agriculture in their broader foresight studies. Other types of studies, such as forecasts and projections (cited in Section 3.1), address the demand side of products from agricultural soils. None of these studies directly addresses soil management, but together, they anticipate an intensification of agricultural production at the global level, which poses threats to soil functions. But the studies also imply opportunities for improved soil management. However, to date, no foresight or similar study has focused directly and comprehensively on the management of agricultural soils. Nevertheless, soil management is the key pressure shaping soil multifunctionality.

This paper presents a review of the drivers of soil management for the exemplary case of Germany as one of the highly industrialized countries with very low yield gaps. The aim was to analyze the existing evidence of emerging trends in soil management practices (Fig. 1) and to identify upcoming and future opportunities and challenges for soil functions that are relevant to be addressed, among others, in experimental research and scenario modeling. This study was conducted in the frame of the German research program “BonaRes—soil as a sustainable resource for the bioeconomy” (www.bonares.de/en/) to inform research and modeling activities. Its implications are also relevant for the wider research community.

Fig. 1
figure 1

Technological development is a key driver of change in soil management. The example is one of the first agricultural robots being close to commercialization, which are small and lightweight, so that they can reduce weight and contact stresses and facilitate smaller-scaled field patterns. As its main task, this robot can make weed control much more efficient. It identifies the weeds with a sensor and sprays each plant individually. The developers are also working on an implement for organic farming. (photo credits: Ecorobotix autonomous robot weeder, 2016)

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2 Materials and methods

2.1 Analytical framework

The conceptual starting point of the analysis was the DPSIR (Driver-Pressure-State-Impact-Response) framework introduced by the European Environment Agency (Smeets and Weterings 1999). “Drivers” are defined as social, economic, or environmental developments that lead to “pressures” being exerted on the environment (Tscherning et al. 2012). In our case, “pressures” are exerted by soil management leading to changes in the “states” of soils regarding their processes and functions. These changes, in turn, lead to different social, economic, or environmental “impacts,” such as climate change mitigation, and may lead to different societal “responses,” e.g., mitigation policies. It is important to note that “pressure” in this context is not necessarily connected to negative outcomes but to any activity that causes changes in soil functions, negatively or positively.

The analytical framework of this study (Fig. 2) builds upon the DPS part of DPSIR. We identified the type of soil management changes (pressures) that may emerge in response to the identified drivers. The drivers were clustered into socio-economic, biophysical, and technological categories. Drivers acted upon pressures (soil management) in two ways, quantitatively and qualitatively:

  1. 1)

    Quantitative changes affect soil management in terms of decreased or increased biomass production. Ceteris paribus, the quantities of production factors are changed, e.g., adding less/more of the same fertilizer with the same application technology as before.

  2. 2)

    Qualitative changes affect specific aspects of soil management qualitatively, for example, by making the crop rotation more diverse.

Fig. 2
figure 2

Analytical framework: Drivers of soil management trigger quantitative and/or qualitative changes in soil management (pressure). Quantitative changes refer to in-/extensification without qualitative changes in the system (more or less of the same input factors such as fertilizers). The changed soil management may lead to changes in soil functions (state)

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We reviewed whether such soil management categories affect soil functions. We refer to the five key soil functions relevant to agricultural soils: (1) the production of food, fiber, and biofuel; (2) water purification and retention; (3) carbon sequestration; (4) habitat for biodiversity; and (5) recycling of nutrients and (agro)chemicals (Schulte et al. 2014, complemented by the item water retention). For quantitative changes (Section 3), we contrasted the extensification and intensification of the production with intensification prioritizing the production function of soils and thus potentially threatening other soil functions. For qualitative changes (Section 4), we contrasted improving and threatening influences on soil functions.

2.2 Literature and document analysis

The material analysis was conducted between January and November 2016 and included a total of 267 sources that were analyzed in the following three steps:

  1. 1)

    The first step was to analyze existing foresight studies, projections, and forecasts for their relevance for agricultural soil management. In this process, we identified drivers of soil management, how they are developing and how they affect soil management. This analysis was based on scientific literature. We preferred peer-reviewed meta-studies and systematic reviews over peer-reviewed reviews over peer-reviewed research studies over gray literature (Table 1). The latter was also included in the analysis because foresight studies have mostly been published as such and not as peer-reviewed literature. The literature search was initially performed with Google Scholar and Web of Science. Because Google Scholar returned more useful results, this search engine was ultimately used.

  2. 2)

    The second step was to identify further drivers of agricultural soil management beyond the future-oriented literature. Important examples are studies that identify correlations between farmers’ attributes and soil conservation behavior and studies that identify correlations between exogenous factors such as dietary changes and global land use changes. This step was fundamental, as documents analyzed in step one addressed agricultural production in general, but none addressed soil management in particular. The literature search followed the same process as step one.

  3. 3)

    The third step was to assess what role the drivers of agricultural soil management, identified in steps one and two, play in Germany, i.e., what the characteristics of drivers in Germany are, and what kind of changes in soil management they may lead to. Sources included scientific evidence, governmental sources, and other sources (Table 1). Governmental sources were used to analyze, if available, statistics and forecasts of some drivers, for example, the changes in farmers’ attributes such as age and education. For public debate on a driver or pressure, the three most relevant German magazines for this analysis (Top Agrar, DLG-Mitteilungen, Agra-Europe), directed at different stakeholder groups, were sighted and selected according to the analytics of the readers of several magazines (Schleyerbach 2009), their own descriptions of their target groups (DLG-Mitteilungen 2016; Agra-Europe 2016e), and the authors’ experiences. Other online information for different stakeholders was taken into account to analyze either the public debate (e.g., a statement of an important lobby group) or to analyze the market and industry trends when there was no current scientific analysis available.

Table 1 Sources of the analyzed material and hierarchy of their selection
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Most sources were analyzed qualitatively with a mixture of an inductive and a deductive approach. For example, the process started out with some knowledge and ideas of drivers. So we looked for evidence of those drivers but also openly for additional drivers. We extended or rearranged our categorization (Fig. 3) of drivers when finding new drivers. Some official statistics were evaluated quantitatively by, for example, calculating percentages of farmers’ attributes in clusters of age.

Fig. 3
figure 3

Overview of the identified drivers of soil management, categories of soil management (pressures) changes, and soil functions (state) that are affected by soil management. Socio-economic, biophysical, and technological drivers affect soil management in terms of changing intensity (quantitative changes) and in five categories of qualitative changes. The pressures together affect soil processes, which in turn affect the interaction between the soil productivity function and the other soil functions

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The approach was influenced by the fact that there is very little literature available that specifically addresses the drivers of soil management. The exception is literature on the adoption of conservation behavior, but this is only a small part in this overall analysis. This is one reason why the study had to be explorative, taking very broad and diverse material into account. Also, the foresight character of the study made it necessary to capture media discussion and to view sources that have not yet been scientifically analyzed or been published in peer-reviewed articles.

Important to note is that prices of agricultural products and market dynamics are, with exceptions, not regarded as the main drivers. Prices are in the medium and long term mainly a translation of the increased or decreased demand for products into financial terms, while the demand in terms of the amount of biomass is the driver of interest here. Several studies, cited in Section 3, have assessed the commodity demand with economic models; thus, market dynamics underlie some of the results.

3 Quantitative changes in pressures on soil functions

A complex net of the drivers and trends of soil management was identified, shown simplified in Fig. 3. Drivers evoking quantitative changes in soil management (intensification and/or extensification by using more or less of the same inputs in the same manner) are listed in Table 2 and further outlined with short narratives in this section. Ceteris paribus, intensification, i.e., producing more biomass from the same land, is connected to higher nutrient, pesticide, and water input and higher harvest frequencies (FAO and ITPS 2015: 60ff.).

Table 2 Drivers and trends of quantitative pressures on soil functions (intensity of soil management) at the global level and for Germany
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Drivers were analyzed at the global and national levels because, in a world of globalized trade, the worldwide demand for agricultural products is relevant for overall production intensities, while national characteristics shape the national reactions to global drivers, i.e., the translation into soil management.

The need for intensification is often asserted by different stakeholders simply due to the growing world population. Many studies have attempted to assess the growing demand for agricultural products. In particular, the studies aiming to quantify future demand are faced with having to make simplifications, such as considering only the most obvious and strong drivers, making assumptions about selected factors or using selected model approaches. In contrast, we abstained from quantification in favor of drawing a multifaceted picture of the drivers.

Globally, current projections of food demand suggest a massive increase derived from population growth and changing diets towards more animal products, which require more inputs from cropland and grassland per calorie than plant products. Changing diets may even surpass the driver of increasing calorie needs (Alexander et al. 2015, Kastner et al. 2012). These two drivers are the greatest in terms of quantitative changes. For example, Godfray and Robinson (2015) found that a range of different studies suggests increases in food demand from approximately 2010 to 2050 of between 50 and 100%, involving a high degree of uncertainty. It is possible that developing countries will start campaigning for healthy diets earlier in their development stages than industrial countries, seeing for example how improving diets and promoting sustainable lifestyles is a global endeavor with the Sustainable Development Goals (United Nations 2015). The digitalization of the world may support this by passing over health and animal welfare trends to parts of the developing world via non-governmental channels. Biomass demand for energy is projected to increase over the long term. At the same time, other energy sources and ways to use solar and wind energy more effectively are likely to be developed, thereby mitigating the increasing demand for biomass-based energy. Demand for biomass for industrial purposes is still low, but some segments grow fast. If the bioeconomy strategies in place in many countries move the trend forward, this is likely to significantly increase biomass demand. Food losses and waste are accounting for the production on approximately one third of agricultural land (FAO 2013b). This proportion may increase with the increased adoption of “Western lifestyles,” but there are movements and policies aiming to reduce food waste; thus, there may be waste reductions that relieve the pressure on agricultural soils. Closing yield gaps means, on the one hand, that production is intensified in some parts of the world. On the other hand, in places in which this intensification starts from a very low level, it must not be associated with soil degradation, but it may be more relevant that it relieves pressure on soils elsewhere. Still, pressure on soils is also likely to increase because less land will be available due to competing land uses, and some land will have reduced production capacities due to soil degradation, climate change, or other factors accounting for yield stagnation. These reduced capacities will place more pressure on the rest of the agricultural soils. There are varying assessments of how much land could be additionally converted to agricultural soils. However, there is convincing evidence that this area is not large, and such conversion should generally be avoided due to negative environmental outcomes.

Overall, it seems that a strong force to increase the production on agricultural land is occurring globally, with only little indication that policymakers and civil societies will succeed to relax biomass demand by addressing, for example, food losses and nutrition habits.

Whether and how this demand to produce more biomass is realized is differentiated locally. Europe on the whole, and Germany in particular, have very low yield gaps (van Grinsven et al. 2015), and thus, very low potential biomass production increases (Mauser et al. 2015: 4) compared to many other world regions. Because of the low yield gap and the yield stagnation in Central and Northern European countries (Wiesmeier et al. 2015), marginal utilities of additional inputs are much lower than in other areas of the world, so the economic incentives to intensify are low. Price relations between inputs and outputs are expected to decrease between 2015 and 2025 in the EU despite increased demand for agricultural products due to higher resource prices (European Commission 2015b). In addition, European agricultural policies include measures promoting extensification (agri-environmental measures, “greening” of the Common Agricultural Policy (CAP) of the EU). Such policies have a mildly increasing trend, which may continue for the foreseeable future (see Section 4.1). In conclusion, for Europe and particularly for Germany, one of the countries with the most industrialized and intensive agriculture, the trends for intensification may have less strength than in many other parts of the world, at least in the coming years. In the long term, the further promotion of the bioeconomy and the longer vegetation periods (climate change) may reinforce the trend towards intensification after all.

4 Qualitative changes in pressures on soil functions (changes in soil management)

This section is organized according to the categories of soil management that were identified as being affected by drivers and trends. Five categories of soil management pressures can be differentiated: (i) general behavior concerning soil functions, (ii) spatial patterns, (iii) crops and rotations, (iv) mechanical pressures, and (v) inputs into the soil (Fig. 3). The last three categories are in line with what Haddaway et al. (2015) identified as relevant soil management pressures leading to different soil organic carbon (SOC) contents of soil (crop rotations, tillage, amendments, and nitrogen fertilizer). “Spatial patterns” were identified as another category, as they are important for some soil functions (biodiversity), and they affect soil degradation processes such as soil erosion. This category supports the argument of Duru et al. (2015) regarding the importance of the spatial organization of cropping systems for ensuring the delivery and resilience of ecosystem services. The first category was identified as an explicit superordinate category because some drivers trigger changes in that direction irrespective of the specific measures taken. Drivers affecting qualitative changes to soil management are listed in the tables together with their sources from the literature, and an indication of whether these trends are expected to increase or decrease soil multifunctionality is included. Short narratives on the more complex interrelationships are given in the subsections; drivers are written in bold italics.

4.1 Behavior concerning soil functions

There are drivers that generally influence whether the soil is managed in favor of maintaining soil functions (Table 3). This means that these drivers motivate or enable farmers to consider taking actions to maintain soil functions in general (often referred to as “conservation behavior”) or to neglect it. Which specific soil management practices are considered is subject to different circumstances.

Table 3 Drivers and trends of behavioral aspects concerning soil functions in Germany
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Consumer demand in Germany and other European countries has trended towards increasing awareness of environmental issues of food production (Table 3). This change is reflected in the increasing demand for organic (Bund Ökologische Lebensmittelwirtschaft 2012, 2016) and local food products (Hempel and Hamm 2016) and the sustained resistance against genetically modified organisms (Emberger-Klein et al. 2016). Foresight studies predict that this trend and the demand for more diverse and specialized food as well as for the traceability and transparency in production will persist (Schindler et al. 2014; Teagasc 2016; Last et al. 2015). At the same time, new information and communication technologies will enable more traceability and information on the impacts of soil management on soil functions. This may feed back towards more explicit demands from consumers. Fountas et al. (2015a) found that emerging farm management information systems may become commercialized in the coming decades that respond to the increasing demand for environmental integration. This improves the technical basis for certification schemes that include aspects of soil management. As a consequence, improved soil management schemes are expected in the future by Teagasc (2016: 63).

Soil management schemes may be realized as part of the Common Agricultural Policy of the European Union (policies) (Table 3), which already includes regulations and funding measures with relevance to soil management. A further “greening” of the CAP is to be expected but with unclear impact. At the European level, better soil governance is not directly underway after the proposal for the Soil Framework Directive failed in 2014. However, soil protection is still a goal of the EU (European Commission 2013), and there are a number of EU policy instruments relevant for soils (Vrebos et al. 2017; Glæsner et al. 2014). Prominently, under pressure of the European Commission, the German government improved the implementation of the Nitrates Directive in 2017 by amending the fertilization law (Agra-Europe 2017)—a several-year-long process showing that policy is going into the direction of protecting natural resources, but with a strong opposing lobby. For Germany, some signals of a movement towards sustainable soil management are evident at national and international policy levels. Most prominently, the UN 2030 Agenda with its Sustainable Development Goals (SDGs) has recently given greater political attention to sustainable soil use (United Nations 2015). The SDGs have been integrated into the German sustainability strategy (Deutsche Bundesregierung 2017) that now acknowledges a stronger role of soils than before (Deutsche Bundesregierung 2002). With the first and revised World Soil Charter, all members of the FAO endorsed the aim to manage soils sustainably, along with some principles and guidelines for action (FAO 1982, 2015b). However, its uptake in concrete policy action remains uncertain (Montanarella 2015: 33). In the sections about climate change and biodiversity loss, more relevant policies are mentioned in association with more specific soil management categories.

There are some attributes of farms and farmers (farm ( er ) s’ attributes) that have been identified as influencing the acknowledgment of soil functions in soil management (Table 3). For Germany, a trend towards a higher education level of farmers, together with the age structure, seems to be the strongest identifiable trend of farms’ and farmers’ characteristics that, together with technological advancements, may lead to an improved consideration of soil multifunctionality. The role of tenure issues, such as whether farmers manage own or rented land, is not well investigated in the German context. These issues may be relevant especially because of the trend in some regions for large farms to be built up by (domestic or foreign) financial investors with weak or short-term bonds to the land.

Soil degradation threats may also drive farmers towards an improved recognition of soil multifunctionality (Table 3). This may be triggered by improved knowledge and information about the extent of soil erosion, compaction, organic matter decline, and soil biodiversity loss and its feedback on yields at specific sites (research, ICT) (Table 3). Especially in the field of soil biodiversity, new insights from research and monitoring are to be expected (Griffiths et al. 2016; Stone et al. 2016).

Climate change (Buth et al. 2015; Gömann et al. 2015) directly drives adaptation to higher temperatures, longer vegetation periods, and more extreme weather events, while mitigation measures, e.g., carbon sequestration, are primarily driven by policies (Paris Agreement 2015; Deutsche Bundesregierung 2016; Bundesministerium für Ernährung und Landwirtschaft 2015b; Ministère de l’Agriculture 2015/2016), which, in turn, incentivize farmers to change management, affecting all categories of soil management described in the following subsections.

In summary, consumer demand in combination with new technologies, research, and the change in farmers’ attributes are the strongest drivers towards improved recognition of soil multifunctionality in soil management that have the potential to counteract the intensification pressure driven by increasing global biomass demands. Policies are not irrelevant, but they do not seem to show strong trends towards or against sustainable soil management. The role of tenure issues is not addressed in the literature for the case of Germany but may be worth investigating further given the fact that the share of rented land was already 60% in Germany in 2013 (Statistisches Bundesamt 2014a).

4.2 Spatial patterns

Spatial patterns of cropping systems determine the spatial extent and distribution of fields and crops as well as the quality of field transition zones, e.g., between different crops, fields, or land use types, including forests and grassland. Field transition zones affect erosion; agricultural biodiversity, likely including soil biodiversity; and biological pest control, allowing reduced pesticide application (Van Oost et al. 2000; Heißenhuber et al. 2014; FAO 2016b; Médiène et al. 2011; Haenke et al. 2014).

4.2.1 Field sizes, field patterns, and transition zones

The trend towards larger machinery for economic reasons (factor costs, especially labor costs) has led to increased field sizes (Björklund et al. 1999; Baessler and Klotz 2006) (Table 4). This situation has destroyed field margins and landscape elements such as hedgerows or small transition zones between crops. Although a trend reversal cannot be identified yet, certainly not for labor costs (European Commission 2015b), field transition zones may increase again due to increased knowledge and awareness about their positive impacts on soil functions (soil degradation threats, research) (Table 4). Due to the adverse short-term cost-benefit relation for farmers, this alone will hardly suffice to motivate farmers to introduce field margins. However, in the coming decades, small, autonomous machines, for which the technology is currently being developed, may become implemented, among others, because the cost of machine work would be decoupled from labor costs (ICT and robotics, see Section 4.3). This would open opportunities for more small-scaled field patterns, especially if politicians create incentives to realize the possibilities. Currently, the green direct payments of CAP (policies) encourage landscape elements, although not very effectively (Pe’er et al. 2016; Zander et al. 2016b), and many, if not all, agri-environmental programs have been and are subsidizing landscape elements, flower strips, or other biotopes (Freese and Keelan 2016) (Table 4). Thus, drivers for smaller-scaled field patterns are evolving but to what degree the chances for this will be realized remains insecure.

Table 4 Drivers and trends regarding spatial patterns of soil management in Germany
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4.2.2 Intercropping and agroforestry

Intercropping uses the positive effects of transition zones within the field by growing at least two crops simultaneously on one field. Similar to intercropping, agroforestry combines conventional agricultural crops or grassland with woody plants. Meta-studies show that intercropping has the potential for sustainable intensification by increasing both total yields in terms of land equivalent ratios and other ecosystem services, among others in temperate regions, including Europe (Pelzer et al. 2014; Yu et al. 2015). This relates to the increasing consumer demand for food and land availability constraints (Table 4). More research is needed to further substantiate this finding, especially for cereal/cereal combinations (Yu et al. 2015). In the case of agroforestry, a similar potential has been detected in review studies and a meta-analysis for Europe (Torralba et al. 2016; Nerlich et al. 2013) and for temperate regions in general (Smith et al. 2013).

Research itself is a driver in this field, increasingly uncovering the potential impacts of intercropping and agroforestry in temperate zones, including Germany (Fagerholm et al. 2016 for agroforestry) (Table 4). Adoption of these practices will depend on their impact on farm income. This will more easily become positive for intercropping than for agroforestry because the latter is connected to higher investment costs (factor costs) and longer return rates (Table 4).

Because of the potential for sustainable intensification and ecosystem services, these systems may get promoted in the future by policies (Table 4). Since 2015, the CAP has recognized agroforestry fields as agricultural land eligible for basic payment from the first pillar, and it allows the financial promotion of agroforestry via the second pillar, recognizing it as an ecological focus area, which is currently not the case in Germany (Bundesministerium für Ernährung und Landwirtschaft 2015b). This shows an actual trend towards these systems, not just in the research arena. Climate change may also contribute to the adoption of both systems (Table 4). Studies reported increased carbon sequestration by intercropping (Yu et al. 2015) and agroforestry (Lorenz and Lal 2014; Smith et al. 2013; Torralba et al. 2016; Nerlich et al. 2013; Upson et al. 2016; Cardinael et al. 2017). Diversification, including measures such as intercropping and agroforestry, is generally associated with making agricultural systems more resilient to biophysical drivers such as climate change (potential for climate change adaptation) (Altieri et al. 2015; Lin 2011).

One of the strongest drivers for adopting intercropping and agroforestry may be technological development in the use of biomass for energy and industry (biomass technology) towards lignocellulosic feedstocks (see Section 4.3.1).

Finally, ICT and robotics may contribute as enabling drivers to the adoption of intercropping and agroforestry (Table 4). These drivers will enable much more precise and small-scaled management with small agricultural robots (see Section 4.4.3).

In summary, it is still very uncertain whether intercropping and agroforestry will become widespread practices in the coming decades. Still, there is a significant trend towards these systems, propelled by several drivers, and upcoming drivers may reinforce this trend.

4.3 Crops and rotations

The choice of crops and crop rotations affect soil functions because crops differ, for example, in their root systems, their interacting biological soil processes, their potential to dissolve nutrients, the degree and duration to which they cover the soil, and the residues they leave after harvest. Thus, they affect, for example, soil organic matter, soil stability and erosion, and soil biota.

4.3.1 Integration of lignocellulosic crops

There are technological and political advancements triggering the increase in lignocellulosic feedstocks for second-generation bioenergy (biomass technology) (Allwright and Taylor 2016; Stolarski et al. 2015; Chum et al. 2015) (Table 5). Aside from integrating these feedstocks directly with traditional crops such as grains or grass in agroforestry, short-rotation coppices (SRCs) with trees and Miscanthus monocultures are discussed and already implemented to a small degree. In addition, the potential of paludiculture for protecting organic soils from drainage and degradation is being discussed (Wissenschaftlicher Beirat Agrarpolitik et al. 2016; Wichmann 2016).

Table 5 Drivers and trends regarding crops and crop rotations in Germany
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These systems are also considered to have some benefits for soil functions (driver soil degradation threats), including carbon sequestration (climate change mitigation) (Voigt 2015 for Miscanthus, Musshoff 2012 for SRC, Wichmann 2016 for paludiculture) (Table 5). The stress tolerance of some second-generation feedstocks such as Miscanthus (Quinn et al. 2015) makes them also of interest for climate change adaptation (Table 5). Responding to the potential for societal benefits, SRC can be acknowledged as an ecological focus area in Germany since the greening of the CAP, if certain specifications are implemented (Bundesministerium für Ernährung und Landwirtschaft 2015b). Some German federal states subsidize the establishment of SRC with up to 45% of investment costs (Fachagentur Nachwachsende Rohstoffe e.V. 2016). Thus, policies currently seem to be a driver for SRC though investment costs (factor costs), and the long payback periods are still barriers (Musshoff 2012).

Thus, the widespread integration of woody crops into agricultural systems is more likely a long-term option rather than a present trend.

4.3.2 Crop varieties

Farmers are expected to adapt to climate change-induced developments such as longer vegetation periods in the long term (past 2040) (Olesen et al. 2011; Mitter et al. 2015) and changed weed systems (Peters and Gerowitt 2014) by using different plant varieties (climate change adaptation) (Table 5). Developing plant varieties in terms of their pathogen tolerance and their defense mechanisms below ground is a research topic that may also become more practically relevant in the future once research has advanced (Johnson et al. 2016; Rasmann et al. 2017) (Table 5). New breeding technologies, such as CRISPR/cas9, can also lead to organisms, including varieties of annual agricultural crops, which can bring risks, such as harming ecosystems (Science for Environment Policy 2016) which could also have an impact on agricultural soils.

4.3.3 Crop rotations: diversity, cover crops, and legumes

For crop rotations, there are drivers in opposite directions: On the one hand, diversifying crop rotations and/or including non-harvested cover crops and legumes induce improved soil functions in terms of nutrient cycling, soil microbial biomass, and soil biota with relevance for plant health, soil carbon content (meta-studies by McDaniel et al. 2014; Poeplau and Don 2015; review by Johnson et al. 2016), and soil structure with relevance for soil erosion (Bronick and Lal 2005). As such, these measures are useful for counteracting soil degradation threats, including soil biodiversity loss, and mitigating climate change (Table 5). These positive aspects for soil functions are the reason they are already subsidized by the CAP green direct payment (Bundesministerium für Ernährung und Landwirtschaft 2015b) and by agri-environmental measures in some German states (Freese and Keelan 2016). The effectiveness of these policy measures is contested, but the further development of agricultural policy may bring more relevant policy incentives (policies) (Table 5). In addition, the German government’s “protein crops strategy,” including influences on the CAP towards the support of grain legumes (Bundesministerium für Ernährung, Landwirtschaft und Verbraucherschutz 2012), seems to be leading to higher shares of legumes on cropland, though currently affecting less than 1% of cropland (Statistisches Bundesamt 2016b; Reckling 2016; Zander et al. 2016a). The positive effects of enhanced crop rotations on soil functions can also be driven by adaptations to climate change because higher carbon contents of soils and better soil structure make agricultural systems more resilient to climate change (Olesen et al. 2011) (Table 5). These circumstances are met by farmers with a general awareness of the relevance of crop rotation for soil fertility (Friedrichsen 2016; Techen 2015).

On the other hand, the economics related to climate change with longer vegetation periods and higher temperatures, if not mitigated by policies, are expected to lead to less diverse/narrower crop rotations in some areas in Germany (Gutzler et al. 2015; Troost and Berger 2015; Peters and Gerowitt 2014) and double cropping, e.g., growing a summer barley after a winter barley, will become possible in some regions (Nendel et al. 2014).

A key driver of crop rotations is demand from consumers, which determines which crops are economically feasible (Table 5). In that respect, the potentially increasing demand for lignocellulosic plants for second-generation bioenergy (biomass technology) seems to be the main driver (see Section 4.3.1). From 2000 until recently, the promotion of bioenergy with the Renewable Energy Sources Act (EEG) (policies) was a driver of less sustainable crop rotations, and presumably also of turning grassland into cropland (Laggner et al. 2014), due to the incentives for high shares of maize in the rotations. Meanwhile, the EU has put a measure into place to stop grassland loss in the context of cross-compliance, and the reforms of the EEG in 2012 and 2014 have reduced incentives to produce maize as feedstock for biogas—and biogas at all—while the 2016 reform (EEG 2017) will likely lead to a stabilization of the policy incentives (Bioenergie e.V. et al. 2016a, b). Additionally, if the demand of consumers is significantly changing towards more organic, more local, and more diverse food (see Section 4.1), then this might already have a small but increasing impact on crop diversity and crop rotations.

Most of these drivers are rather long term. A policy change towards diversified crop rotations may be the fastest but not the strongest driver.

4.4 Mechanical pressures on soil

Mechanical pressures on soil can damage soil structure, lead to compaction and erosion, and disturb soil biota, all severely damaging soil functions, including the production function (Schjønning et al. 2015).

4.4.1 Tillage

Reduced tillage is a widespread practice in Germany with 38% of cropland having been under reduced tillage and 1% under zero tillage in 2009/2010 (Statistisches Bundesamt 2010). More innovative and not yet widespread forms are strip-tillage and controlled traffic farming (CTF) as well as innovative methods of subsoil management, some of which go beyond tillage (see Section 4.4.2).

High costs of labor and fossil fuels (factor costs) are drivers of reduced tillage (Flessa et al. 2012; Techen 2015) (Table 6). Factor costs are likely to increase (European Commission 2015b). In addition, awareness of soil degradation threats (farmers’ attributes) is an incentive for farmers to reduce tillage (Techen 2015) (Table 6). Both are likely established factors rather than trends, but they may be drivers for the diffusion of new (strip-till, CTF) or future technologies (ICT and robotics) (Table 6). In addition, climate change adaptation is expected to drive reduced tillage because it is an important water-saving practice in some European countries, including the eastern half of Germany (Olesen et al. 2011). Reduced tillage is also discussed in the context of climate change mitigation because of its beneficial effect on carbon sequestration in the upper soil layer (e.g., Zandersen et al. 2016), although this effect is strongly contested (Powlson et al. 2014; Baker et al. 2007; Blanco-Canqui and Lal 2008; VandenBygaart 2016). Reduced tillage had been subsidized in some German states in the past (Grajewski and Schmidt 2015). Currently, there are still agri-environmental measures (policies) for reduced tillage in 4 out of the 16 German states, all but one specifically for strip-tillage and zero tillage (Freese and Keelan 2016).

Table 6 Drivers and trends regarding mechanical pressures on soil management in Germany
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One trend may potentially reduce the share of reduced tillage. There are political debates on pesticide use reflecting consumers’ concerns (consumers’ demand) (Table 6). The near ban of glyphosate and the ban of neonicotinoids in neighboring France (policies) are examples. A ban of glyphosate would not just mean less pesticide input, it would very likely lead to more frequent tillage and an increased share of tillage with the plow, at least until new pesticides will substitute glyphosate (Kehlenbeck et al. 2015, Section 4.5.2).

Additionally, site-specific tillage (technology , ICT) (Fig. 4), which determines the tillage depth according to factors such as soil type and moisture, has the potential to make tillage more beneficial for the soils, especially once better on-the-go soil moisture sensors are available (Auernhammer and Demmel 2015: 314 f., similarly, Jørgensen 2014; Stoorvogel et al. 2015: 53).

Fig. 4
figure 4

In front of the tractor, a sensor detects soil texture via the conductivity. Sandy soil with low conductivity is being tilled at a deeper working depth than a clayey soil with high conductivity. Data acquisition and implementation are done in real time. (photo credits: Hans-Heinrich Voßhenrich)

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The bottom line is that the existing drivers in favor of the adoption of improved and new tillage technologies may be counteracted in the short to medium term by pesticide restrictive policies and investment costs of new technologies.

4.4.2 Subsoil management

The management of subsoil has different facets. One is subsoiling, that is deep plowing to break the plow layer and traffic-induced compaction, and in some cases, adding organic material to the subsoil. This approach can be used in combination with subsequent no-till to improve water storage and availability for plants (Kassam et al. 2013). The other aspect of subsoiling is to breed and cultivate suitable plants, manipulating soil fauna and microorganisms, also in combination with reduced tillage (Lorenz and Lal 2005; Kell 2012).

Subsoil compaction from heavy machinery and plowing is a soil degradation threat in Europe, including Germany (Jones et al. 2012) (Table 6). At the same time, it is very difficult to recognize and is thus not sufficiently addressed by farmers (Jones et al. 2012). Research is a key driver here because potential new measures of and additional arguments for subsoil management seem to be primarily discussed within the scientific community. Therein, subsoil management is discussed in terms of sequestering carbon (climate change mitigation) (Kell 2012; Alcantara et al. 2016; Lorenz and Lal 2005), water conserving tillage (climate change adaptation) (Sang et al. 2016), and phosphorous efficiency (resource scarcity) (Ekelöf et al. 2015; Zhang et al. 2016). Thus, research is now providing more arguments for subsoil management in relation to current societal challenges, thereby potentially creating a meaningful impact. Especially in terms of C sequestration, the subsoil is understood to be a long-term sink because of the physical protection of the overlying topsoil. Differences in the subsoil texture compared to the topsoil may as well affect the carbon sequestration potential (Alcantara et al. 2016). The research fits well with current policies of the UNFCCC’s Paris Agreement (Paris Agreement 2015) and the “4 per 1000” initiative (Ministère de l’Agriculture 2015/2016), of which Germany is part. However, Germany’s “National Climate Action Plan for 2050” (Deutsche Bundesregierung 2016) does not entail carbon sequestration in mineral arable soils, nor is it identified as a relevant measure in the recent national experts’ report on climate change mitigation in the agricultural and neighboring sectors (Wissenschaftlicher Beirat Agrarpolitik et al. 2016). In addition, the costs (factor costs) of deep tillage (Chamen et al. 2015) are a natural opponent of that aspect of this trend, and factor costs are likely to increase (European Commission 2015b).

Overall, with research in an early stage still being the main driver of modern subsoil management that supports soil functions, while policy drivers are undetermined, and factor costs are hampering, the development of subsoil management is uncertain.

4.4.3 Weight and contact stresses

High labor costs (factor costs) and the development of agricultural technology have been driving an increase in the weight of machinery for decades in Europe (Schjønning et al. 2015) (Table 6). Some measures to address compaction have offset part of the increasing pressure but not sufficient to reverse the trend of increasing compaction (Jones et al. 2012). Similarly, high labor costs seem to hamper the adoption of such measures because they require more working and/or waiting time, for example, to adjust tire pressure between the field and the road and avoiding driving in the fields when the soil is too wet (Chamen et al. 2003). A trend reversal cannot be identified currently, certainly not for labor costs (European Commission 2015b) and not for the weight of machines (Jones et al. 2012).

Still, in the medium to long term, soil compaction can decrease yields (Chamen et al. 2015; Schjønning et al. 2015). Based on spot tests, Marahrens et al. (2015) estimated that compaction has already led to soil functions being impaired on 20% of the German cropland. Approximately 50% of German soils are estimated to be vulnerable to compaction (Marahrens et al. 2015). Thus, compaction as a soil degradation threat is a driver of research and maybe a driver of developing and adopting less compacting technologies.

One option is “controlled traffic farming” (CTF) (technology), which has been investigated and adopted mostly in other parts of the world, especially in Australia (Antille et al. 2015; Demmel et al. 2012) (Table 6). For European conditions, no unequivocal knowledge of the impacts of the approach is available (Chamen et al. 2015). Practitioners seem to be skeptical about the usefulness of CTF in Germany (Preuße 2016). Research on CTF is occurring in some European countries, including Germany, and may drive its adoption in the long term (Demmel et al. 2012) (Table 6).

A further option for reducing mechanical stress is decision support systems (DSSs) that optimize field traffic more individually (research and technology) (Table 6). The first step is calculating fieldwork patterns and guiding the tractors so that minimal overlap occurs. This practice also saves labor costs (factor costs) due to time savings (Auernhammer and Demmel 2015), which may drive its adoption. Automatic tire pressure regulation is currently being developed (Brunotte and Lorenz 2015). Further, DSSs are being developed that can integrate more soil data from different sources and optimize routes, loads, and tire pressure in terms of soil compaction (Bochtis et al. 2012; Lorenz et al. 2016). Such technologies still have challenges in the areas of on-the-go sensing of soil characteristics, sensor/data fusion, and generating practical decision support (Bechar and Vigneault 2016; Han et al. 2015; Weltzien and Gebbers 2016). In addition, improved DSSs are being developed to determine the days of trafficability and workability for the specific field operations (Edwards et al. 2016; Lorenz et al. 2016).

In the long term, ICT and robotics development may lead to much lighter machines. For some purposes, small, lightweight robots are being developed, and few first variants are already on the market or shortly before commercialization (ecoRobotix Ltd. 2016 (Fig. 1); Naïo Technologies 2016a, b; Rowbot Systems 2016). Their further adoption still faces technological and organizational challenges as well as legal issues (Auernhammer and Demmel 2015). Nonetheless, broad implementation of small robot fleets is envisioned (Auernhammer and Demmel 2015; Blackmore 2015) and prepared by researchers (e.g., Chevalier et al. 2015; Conesa-Muñoz et al. 2015; Liebisch et al. 2016) and agricultural technologies companies (AGCO GmbH and Fendt-Marketing 2015). The fact that those agricultural robots are unmanned vehicles that are envisioned to operate as fleets will disconnect the weight of the machines from labor costs. Their large-scale adoption could relieve much pressure from the soils, while there is no scientific evidence yet that shows where there is an optimal balance between stress from machine size/weight and stress from the frequency of running over the field.

Thus, research and technological development ( technology, ICT and robotics), together with factor costs of the farms, drive measures that are likely to bring some relief to the weight and contact stresses of soils in the short and long term if the evolving opportunities are realized.

4.5 Inputs into the soil

Inputs into the soil comprise fertilizers, pesticides, organic input, biotic components, and water. On the one hand, inputs into the soil can enhance soil functions. For example, manure delivers organic material and nutrients to the soil. On the other hand, inputs can harm soil functions, such as when pesticides disturb the soil biological system.

4.5.1 Precise application

The efficiency of resource use, such as fertilizers and pesticides, can be improved with new technologies. Factor costs (Schindler et al. 2014), increasing with resource scarcity, and consumer demand concerning environmental issues (see Section 4.1) are drivers for this (Table 7). Examples are the use of small robots for precise herbicide application on or mechanical destruction of weeds identified with sensors (Meuli 2016) (Fig. 1). Needed technologies, including robots, drones, (on-the-go) sensors for soil characteristics, data fusion algorithms, translation into decision-support systems, infrastructure with GNSS (global navigation satellite system), and mobile networks, are under development (ICT and robotics). Thus, a more precise application can be expected in the long term.

Table 7 Drivers and trends regarding the use of soil inputs in Germany
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4.5.2 Pesticides

Aside from the precision of pesticide application (Section 4.5.1), the authorization of pesticides may become more strict. As outlined in Section 4.4.1, consumer demand is establishing a trend towards more pesticide restrictive policies (Table 7). The outcome of this ongoing debate is still uncertain. The primary effects of a ban of glyphosate would likely be decreased chemical disturbances of soil biota and decreased emissions of pesticides and their metabolites to other environmental media. This is because for arable land, there are currently almost no appropriate chemical alternatives (Kehlenbeck et al. 2015). Instead, more physical disturbances of soils because of increased tillage with the plow would most likely occur in the short-term (Section 4.4.1). In the medium or long term, a ban could result in increased use of other pesticides, which may be more or less harmful to the environment than glyphosate (Kehlenbeck et al. 2015). New pesticides may become available with yet unknown properties regarding persistence, mobility, and interference with soil biodiversity.

Climate change is likely to alter and partially increase weed pressures (Peters and Gerowitt 2014) and other pests in Germany and Central Europe (Richerzhagen et al. 2011; Juroszek and von Tiedemann 2013; Lamichhane et al. 2016) (Table 7). This factor must affect plant protection strategies, including pesticide application. The trends are still uncertain (Juroszek and von Tiedemann 2013; Peters et al. 2014).

Enhancing soil biodiversity can strengthen soil resilience towards pathogens. In their review, Johnson et al. (2016) find significant long-term potential of applying, for example, biocontrol agents such as entomopathogenic nematodes to the soil, affecting soil biota while considerable research still seems to be required to effectively reduce pesticide application, making research a driver (Table 7).

With highly insecure policy development and climate change impacts and new technologies still being in the research stage, no clear trend can be identified for utilization of pesticides (aside from more precise application).

4.5.3 Organic input

Farmers have long been aware of the important role of organic matter in soil fertility. For example, approximately half of 694 Hessian farmers who grow cover crops named the humus balance as one of their motivations (Techen et al. 2015: 75). Maintaining the soil organic matter level was relevant for cross-compliance from 2005 to 2014 as an alternative to some crop rotation standards (DirektZahlVerpflV § 3).

There is no sign that organic matter decline (soil degradation threats) is a singular driver for changes in soil management even though in combination with other drivers, it does play a role in changing soil management (Table 7). Orgiazzi et al. (2016) found that organic matter decline in agricultural soils was one of the two highest threats to soil biodiversity (soil degradation threats). Soil biodiversity loss may induce a trend towards an increased organic input into the soil, as research brings new insights along with better monitoring in the EU (Griffiths et al. 2016; Stone et al. 2016) and societal goals and policies are in place (COP to the CBD 2010a, b; Bundesministerium für Umwelt, Naturschutz, Bau und Reaktorsicherheit 2007). Reviews showed that the effects of long-term organic amendments such as compost had very positive effects on soil microbial biomass, enzymatic activity (Diacono and Montemurro 2010), and biodiversity (Larkin 2015). Another review showed that amendments such as biochar can enhance soil biodiversity, but there is still much need for further research (Thies et al. 2015). A related measure, also increasing organic input and microbial biomass, is growing cover crops as green manure (see Section 4.3.3). Agroforestry and other systems, including perennials, discussed in Sections 4.2 and 4.3.1, also increase organic matter input and improve soil invertebrate communities and soil biodiversity as a whole (Smith et al. 2013; Berndes et al. 2015).

In addition, by increasing SOC, organic inputs are strongly linked to climate change mitigation and adaptation, e.g., by putting organic matter into the subsoil (Alcantara et al. 2016).

Although biomass production for energy and industry (biomass technology) offers potential opportunities for increased organic input from cultivating lignocellulosic perennials in the future (see Section 4.3.1), it has opposite effects as well. The use of plant residues for energy production and industry has been identified as a method to avoid directly losing acreage for food production (Long et al. 2015). This class of feedstock may be strengthened to some degree by breeding dual-purpose crops (Caicedo et al. 2016). Withholding plant residues can put considerable pressure on soils by preventing the maintenance of soil organic matter with all its functions and ecosystem services (Berndes et al. 2015). Considering this circumstance, Weiser et al. (2014) still estimate that between 53 and 89% of the technical potential of straw in Germany could be sustainably used for bioenergy. In the short run, it is likely that only a small share of this potential will be used because of technical constraints such as low energy density and long transport distances due to dispersed cultivation (Hennig et al. 2016). In the long run, technical circumstances may improve, for example, through further development and by removing institutional barriers of market uptake of the torrefaction technology (Hennig et al. 2016; Thrän et al. 2016). Thus, in the future, the usage of plant residues may become a pressure on agricultural soils depending on technological and political developments.

Even though there are drivers pointing to opposing directions, it does seem like the relevance of organic input is gaining broader awareness, and this may lead to actions counteracting organic matter decline in places where it is relevant.

4.5.4 New fertilizers from recycled nutrients

The recycling of substances such as sludge and slurry in fertilizer production, such as phosphate, is a topic of research and technology development and discussion in academia, industry, and politics. This process may have different influences on soils, including its contamination with substances like heavy metals, depending on the original material and its treatment (Desmidt et al. 2015; Montag et al. 2015).

The drivers for such recycling are factor costs and especially resource scarcity. In Germany, some agricultural soils are oversupplied with phosphorous (P) to the extent that it is a threat to other ecosystems (Marahrens et al. 2015: 19) (Table 7). Other agricultural soils are rather poorly supplied. An analysis of the data from most German federal states showed that 28% of cropland and 51% of grassland are undersupplied with P (Trott 2010). Processes like improved slurry separation may contribute to better distributing P and N (nitrogen) between regions by making the nutrients more worthy of transport (Hjorth et al. 2010). The necessity for efficient P use is a topic at the interface of research and the political agenda in Germany (Kommission Bodenschutz beim Umweltbundesamt 2015; Wissenschaftlicher Beirat für Düngungsfragen beim BMELV 2011), and the European Commission is paving the way for adjusted fertilizer regulations (European Commission 2016c) in the context of the Action Plan for the Circular Economy (European Commission 2015a) and the Raw Materials Strategy (Ekardt et al. 2015) (policies). In addition, part of the fertilizer industry is working towards recycling nutrients while emphasizing that the framework conditions are not yet fully developed (Fertilizers Europe 2016a, b) (research).

Thus, there is a clear trend towards recycling nutrients for fertilizers while it is still unsure when and what kind of change exactly will occur.

4.5.5 Inoculation of soil and seeds with, and management of, mutualists of crops and natural enemies of pests

Biotic inoculation of soils and seeds is seen by some authors (Johnson et al. 2016, Kergunteuil et al. 2016) as an evolving, promising method for plant performance and protection.

Important below ground mutualists for crops that can improve crop productivity and promote indirect plant defenses, among others when added by inoculation, are bacteria and fungi (Rasmann et al. 2017). Positive effects on plant growth by soil inoculation with bacteria or fungi were found, for example, in wheat in Sicily (Saia et al. 2015a), China (Zhang et al. 2014), and Egypt (El-Sirafy et al. 2006), whereas findings of negative effects (Verbruggen et al. 2012) underline that the interdependencies are not well understood yet (Saia et al. 2015b) (Table 7).

Natural enemies of belowground pests are manifold. They include viruses, bacteria, fungi, nematodes, and arthropods (Kergunteuil et al. 2016). High potential for inoculation with such organisms is seen for several types of natural enemies, such as entomopathogenic nematodes (EPNs) (Johnson et al. 2016 and Kergunteuil et al. 2016) and mixes, such as EPNs with Bacillus thuringiensis (Kergunteuil et al. 2016). For some organisms, effects on non-targeted organisms are not sufficiently studied yet. But in general, negative effects are much less expected than from chemical pesticides (Kergunteuil et al. 2016). Wide application of inoculation with natural enemies is still hindered by technical and economic obstacles, including factor costs (Johnson et al. 2016 and Kergunteuil et al. 2016), so that currently, research, including industrial research, seems to be the decisive driver towards inoculation of soil with natural enemies.

While inoculation is an innovative method that may evolve and gain adoption, there are more conventional ways to promote local mutualists of crops and natural enemies of pests, such as crop rotations, cover crops and intercropping (Johnson et al. 2016, Larkin 2015), organic amendments, especially compost (Larkin 2015), and breeding plants to attract mutualists (Rasmann et al. 2017).

Inoculation of soil with, and management of, soil biota is the pressure most explicitly associated with soil biodiversity loss as a driver (soil degradation threats) (Section 4.5.3). Inoculation may still be a rather expensive measure for compensating for soil biodiversity loss, carrying also the risk of damaging non-targeted organisms if measures are not studied and regulated enough (policies). In the long run, it is likely to become cheaper. Farmers may perceive this practice as an easy option that does not require as substantial changes to the production systems as other measures, even though the effectiveness of the inoculation may strongly depend on supporting measures (Johnson et al. 2016). Teagasc (2016) expects that by 2035, it will be routine in agriculture to collect genetic data from soil biota (technology) and use the information together with available data from other sources for management decisions, including isolating and utilizing endophytes to enhance the soil biome. There are still significant challenges to overcome to reach this goal, such as to develop sensors and algorithms (Section 4.5.1).

Pesticides will likely be the cheapest version for fighting plant diseases in the near future. But upcoming research and technology together with increased awareness of the relevance of soil biota may pave the way towards the wide-spread adoption of inoculation with crop mutualists and natural enemies of pests in the future and potentially also towards agricultural management which promotes the local soil biotic communities.

4.5.6 Irrigation

Irrigation is not widespread in Germany. In 2012, only 4% of German agricultural areas had the infrastructure for irrigation and only 2% were actually irrigated (Statistisches Bundesamt 2014c).

Several studies found economic potential for irrigation in some areas in Germany at present and increasingly in the future, towards 2070, due to climate change, with high variabilities among regions and soil types (Nendel et al. 2014; Münch et al. 2014; Riediger et al. 2016) (Table 7). Conflicts with other water uses can occur in drier years in northeastern Germany (Steidl et al. 2015), restricted water extraction rights may hamper irrigation, and investments in irrigation infrastructure are less likely on rented land (Münch et al. 2014). At the same time, even in one of the German states with the lowest annual rainfall, Brandenburg, Gutzler et al. (2015) found that water availability would likely be a problem in only 2 out of 14 districts.

Thus, there is a clear trend towards an increased introduction of irrigation in Germany as a reaction to climate change in the long run.

5 Conclusions

The analysis of the drivers and trends of soil management in Germany present challenges as well as opportunities for maintaining or improving soil functions presently and in the coming decades. Challenges stem largely from agricultural intensification, which will likely have less impact in Germany than worldwide. More challenges stem mainly from factor costs and risks associated with new practices. Factor costs are projected to remain stable or even increase in relation to the product prices and are an obstacle to the adoption of some beneficial practices, more so in short than in the long term. Risks usually come along with emerging practices because their impacts are not sufficiently understood. There are, however, also great opportunities for agricultural soils posed especially by the technological development towards including smaller and lighter machines and more precise management, by research that is increasingly uncovering positive effects of some soil improving production methods on soil quality and yield development, and by a societal will to support sustainable production methods or subsidiary aspects such as the SOC content of agricultural soils.

Some solutions for the challenges will be developed and opportunities seized by farmers and the farming industry; some changes will be initiated by policy measures. However, the realization of opportunities is not self-evident. Soil and agricultural research can play a vital role in developing sustainable and effective methods of soil management in this framework of drivers, for example, to incorporate lignocellulosic crops in agricultural productions systems to seize the opportunities stemming from improved biomass technologies and policy strategies. It is also crucial for researchers to cooperate in analyzing the unfolding management changes, their alternatives, and their impacts on soil processes so that they can provide evidence for sound suggestions to farmers, authorities, politicians, and society. Basic and applied research must interact in a systemic approach to better understand the soil reaction to changing management and to understand the value of soil functions for societal value systems, particularly in terms of ecosystem services, resource efficiency, and ethical and equity considerations. Only then appropriate governance systems can be developed that integrate bioeconomy with sustainable development targets.

The analysis showed that for many upcoming management practices, little scientific evidence about their effect on soil processes and functions exists, especially on the habitat for biodiversity function. Researchers will need to further develop knowledge about the interaction between soil management and soil functions. To capture the long-term impacts of potentially drastic changes under semi-controlled conditions, long-term field experiments are very valuable. For example, new fertilizers added over a long period potentially accumulate substances, which do not seem relevant in the short-term observation. The analysis particularly requires a systemic view on the soil processes and an interdisciplinary approach involving soil scientists, agricultural scientists, natural scientists, and socio-economic scientists, and the latter to also conduct sustainability assessments of soil management trends that bring a wider understanding of intended and unintended impacts of soil management on sustainability targets. Cooperation with practitioners may improve research results to be well-founded and accepted by farmers.

This review showed that there are a number of changes that might occur in agricultural soil management depending on how different drivers develop. On this basis, future soil management scenarios can be built in the frame of different driver configurations to further determine crucial research topics and needs for action.

The conclusions are not just true for Germany but can be transferred generally to other countries. Many drivers presented here are global, such as food demand and aspects of technological development, or European, such as many of the policies. In addition, for each country, there are distinctions such as the climate, infrastructure, and educational level of the farmers. Our driver-pressures framework for soil management (Fig. 2) can be useful for researchers analyzing soil management and trends in other countries. With additional case studies, a more robust, generic framework may be developed.