On the effects that motivate pesticide use in perspective of designing a cropping system without pesticides but with mineral fertilizer—a review

In the future, a cropping system that guarantees food security by delivering high yields and, simultaneously, protects our environment is desperately needed. This can be achieved through a cropping system that waives chemical synthetic plant protection products, which endanger, for example, biodiversity and water resources. However, such a system, referred to here as the mineral-ecological cropping system (MECS), should still allow for the usage of mineral fertilizers to ensure high yields. It can be thought of as a compromise between the current conventional and organic cropping systems. This article presents a comprehensive literature review on the economic, social, and environmental effects of pesticides and the resulting reasons farmers have to use (or not use) them. Hereby, regarding future pesticide reduction, we identify hindrances and potential benefits that could be mobilized to design the MECS. The major points are the following: in a MECS, (1) it is expected that yields and temporal stability of yields will be higher than in organic farming, but lower than in conventional farming; (2) profitability might suffer due to high input costs and energy consumption; (3) it is expected that soil fertility and biodiversity protection will increase along with the promotion of alternative disease and pest control measures; (4) crop rotations will be wider and more diverse than in conventional farming; (5) mineral fertilizer cannot be optimally used by the crops unless a balanced supply of nitrogen is achieved. Farmers who want to switch to MECS should be compensated as they are likely to experience higher costs and lower yield and yield stability. The lessons learned from this review will help to progress toward an innovative and sustainable cropping system. Further research should focus on rational farmers’ adaptation possibilities when abandoning pesticides while still using mineral fertilizers.


Introduction
In the recent past, the use of pesticides in agriculture has been repeatedly criticized due to their effects on the environment and on human health. A recent report, for instance, by the German Ministry for the Environment (Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit) and Bundesamt für Naturschutz states that for approximately one third of the brood-bird species that require the agriculturally used area for breeding the populations have decreased in the past 12 years (BMU 2020). Essential causes of this development are especially high nutrient and pesticide inputs and the intensification or abandonment of land use, including traditional forms of land use. This concern has resulted in strict government regulation of pesticides and increased demand for organic agriculture (Sexton 2007).
However, this stands in contrast to the insufficient food supply in some regions of the world. In addition, agricultural land is also used for purposes other than growing food crops, for example, for the production of biofuels. This puts more pressure on agriculture and makes increased productivity necessary (Sexton 2007). Several scholars express the need for a practical farming system that simultaneously ensures livelihoods for farmers, food security, and reduced environmental impact (Foley et al. 2011;Seufert et al. 2012;Sexton 2007;Worzewski 2022). Hence, even though this topic is highly relevant, to our knowledge, there is no existing comprehensive review of the literature on it.
Against this backdrop, researchers are currently developing the concept of a mineral-ecological cropping system (MECS) (see Fig. 1). MECS aims at a possible solution to the above-outlined dilemma by abandoning pesticides, using the latest automated and digitalized technologies, and following most principles of organic agriculture, however, without banning mineral fertilizer (Zimmermann et al. 2021). Therefore, MECS can be thought of as a middle ground between conventional and organic cropping systems. With regard to implementing such a cropping system, it is important to thoroughly assess and summarize all economic, social, and environmental effects and motivations related to pesticide usage or bans. As this has not yet been done in a systematic way and as the corresponding knowledge is dispersed over many publications, a comprehensive literature review of the corresponding effects and reasons is provided here. Our focus is mostly on the main field crops grown in the temperate climate zone. Based on this review, one can draw conclusions that could later be mobilized to design a MECS.
At first glance, farmers use pesticides because of their positive effects on crop yields and crop qualities. However, these positive effects may be accompanied by some negative side effects. By "effect," we understand a perceived or an expected impact, which (being either positive or negative) has a certain direction and a certain magnitude. In addition to the (physical) effects of pesticides, we are particularly interested in the related (economic and social) reasons farmers have to use pesticides, as well as in the (environmental and social) reasons against using them. These reasons are important to understand current cultivation practices. They determine the motivation for pesticide use and need to be accounted for when designing an innovative cropping system that is accepted by farmers. Hence, answering the question of why farmers use pesticides is necessary. Only if the needs of farmers are satisfied will they accept an innovative farming system (Moss 2019). In this context, this work also investigates whether there is a relationship between pesticide and mineral fertilizer usage and whether there is a so-called insurance aspect when applying pesticides. On this ground, assumptions will be made on how MECS may alter conventional cropping system techniques to be economically feasible and environmentally sustainable. Thus, the following research questions are raised: (1) What are the main reasons that determine pesticide usage? (2) How important are mineral fertilizers for high and stable yields, and is there a correlation between fertilizer use and pesticide input (e.g., resulting from an interaction between nitrogen input and pests)? (3) What are the main recommendations that can be distilled from the literature to design the MECS?
This literature review is structured as follows: In Section 2, we explain the material and methods used. In Section 3, the results of the literature review about crop losses and pesticide usage in general with a focus on the questions of why (or why not) farmers do use pesticides are presented and discussed. In Section 4, we summarize the answers to the above research questions and give recommendations for designing the MECS.

Material and methods
This review builds on researched literature in order to provide an overview of the latest knowledge. The overall goal is to review the literature with the aim of drawing economically, socially, and ecologically motivated conclusions for designing MECSs.
First, this work concentrates on pesticide usage. The approach includes a systematic literature review of mostly peer-reviewed scientific papers. Academic search databases were searched using the keywords given in Table 1. For example, reports on the use of innovative plant protection methods and trials of no pesticide usage were screened. In addition, attention was also paid to articles dealing with sustainable crop protection practices such as integrated pest management (IPM), as one may derive important insights from cropping systems similar to MECS. Information was also obtained from public institutions such as the German Federal Ministry for the Environment (BMU), that deal with this topic. For a better overview, the reviewed literature is classified into economic, social, and environmental categories, (see the tables below). However, it needs to be recognized that certain pesticide effects are relevant for two categories.
In this work, the term pesticides refer to chemical synthetic plant protection products and cover the following categories: herbicides, fungicides, bactericides, insecticides and acaricides, haulm destructors and moss killers, molluscicides, plant growth regulators, and other plant protection products. Furthermore, the term "cropping system" denotes the way a particular field is managed over time with certain crops, crop rotations, and management techniques (Lamichhane et al. 2016). It should be noted that the main concern was about open-field crops (i.e., excluding horticulture in greenhouses, etc.).
Our screening generated a list of 58 articles about the effects and reasons for pesticide usage or rejection, which is the basis for this work (see Tables 2 and 3). It should be noted that some articles gave both reasons for and reasons against pesticide usage. In total, 33 articles gave reasons for pesticide use, and 37 gave reasons for rejection. To reflect the current knowledge, mainly papers published after 2000 were considered. Although this keeps the number of articles within limits, we are confident to address all relevant aspects. Figure 2 shows the categorization (economic, social, and environmental according to the three dimensions of sustainability) of the literature, illustrating that some articles give more than one reason in various categories. Therefore, the figures of the categories overlap. There is a lot of research that focuses on the economic effects of and reasons for pesticide use, and less literature that addresses environmental aspects (see Fig. 2a). In contrast, Fig. 2b shows that among the articles with arguments against pesticide use, most address environmental concerns.
Our second focus is on cropping systems with mineral fertilizer and its interaction with plant pests, as the usage of mineral fertilizers is allowed in MECS whereas pesticides are forbidden. Thus, a literature review of recent  Crissman et al. (1994) Case study about pesticide usage in potato production Pesticides are necessary for potato production, but there is a tradeoff between farmer's health and high yields Economic Social Wilson and Tisdell (2001) One reason for pesticide usage is higher yields due to pesticides, also farmers are locked into using unsustainable techniques (pesticides) because switching is very costly, it takes extension services, and an industry that provides resistant varieties Economic Oerke (2006) Analysis of crop losses due to pests of main crops (wheat, rice, maize, potatoes, soy, cotton) grown in the world and definition of quantitative and qualitative losses, estimations of how much of the yields are saved due to pesticides (yield loss in %) Economic Social Environment Cooper and Dobson (2007) Analysis of the benefits of pesticides identifies a number of primary and secondary benefits, including higher yield, better crop quality, and higher efficiency, which contributes to food security and food safety Reduced soil erosion due to less tillage Economic Deike et al. (2008) Case study of two experiments in Germany and Denmark about crop rotations, soil tillage, and pesticide usage: They find that yield is more influenced by crop rotation than by pesticides or tillage; pesticides can increase yield, energy and nitrogen use efficiency Social Chikowo et al. (2009) Data from 6 years of integrated weed management experiment with 4 cropping systems: higher complexity of the systems when no fungicides were used Social Lamine et al. (2010) Analysis of decreasing pesticide dependency in several countries in Europe All stakeholders along the chain have to support a transition toward sustainable farming in order to break the lock-in effect Social Meissle et al. (2010) Data from eleven regions in Europe where maize is grown in order to understand the use of pesticide alternatives Farmer would switch to alternative methods if there was more trained labor and if they had suitable equipment and extension services that provide knowledge Social Lamine (2011) Paper about prerequisites of changing to integrated pest management or organic agriculture Escaping the lock-in effect by getting involved with extension services, support from public policies, and changing consumption of costumers Economic Social Jacquet et al. (2011) Analysis of the effects of decreasing pesticide usage by farmers in France and the possibility of reducing pesticides by 30% without compromising the income of the farmers; but farmers are reluctant to decrease pesticide use due to their risk-averse attitude and using pesticides is more convenient; another reason for pesticide usage is the lock-in effect Economic Bürger et al. (2012) Analysis of winter wheat grown in 2001-2007 in Germany; the amount of pesticides used is influenced by agronomic conditions (weather, soil), as well as by the farmer's risk attitude Economic Ponti et al. (2012) Literature review that compares datasets of conventional and organic yield On average, organic yield is 20% lower than conventional yield, but this varies strongly among crops and regions Economic Seufert et al. (2012) Analysis of yield data: in some cases, organic yield can nearly be as high as conventional depending on crop types and regional and management conditions, but in general, organic yield is up to 34% lower than conventional yield Economic Social Nave et al. (2013) Interview of 71 farmers in France about their reluctance to switch to farming with less pesticides The authors found that farmers who use high amounts of pesticides want to achieve high profitability, but low-input-and medium-input farmers achieve higher profitability; the study shows that extension services and knowledge have an important role in converting to low-pesticide agriculture Economic Social Environment Noleppa and von Witzke (2013) Analysis of two scenarios: first, farming with fungicide compared to a situation where no fungicide is used, and second, conventional arable agriculture compared to organic: the authors conclude that pesticides in general and especially fungicides are important for high yield and higher (energy) efficiency for the main crops grown in Germany; this also plays a role for food security and lower greenhouse gas emissions Economic Hossard et al. (2014) Analysis of yield loss due to reduced pesticide use in winter wheat in France; 5-13% yield losses due to a pesticide reduction of 50%, zero pesticide usage results in 24.3-33% yield loss Economic Skevas et al. (2014) Analysis of the performance of farms from 2003-2007 in the Netherlands with a focus on pesticide use and its negative effects on the environment: Results show that many farms overuse inputs (fertilizer and pesticides), farmers overuse risk-reducing inputs in order to manage risks experiments is presented, but some older literature was also reviewed (see Table 4). We found and screened 17 sources. Again, academic search databases were searched using different keywords (see Table 5). Of particular interest in this context is the impact of mineral fertilizer on yield and yield stability, its effects on pests, and its possible correlation to pesticide usage. The amount of literature found on this topic was less than the literature dealing with pesticide use in general. Astonishingly, we did not find many recent research results on the interaction between mineral fertilizer input and pest occurrence/pesticide use.

Results and discussion
From the 1950s on, the green revolution caused a tremendous increase in food production, mainly in the yield of grains such as wheat, rice, and maize (Tilman 1999). This  Bail et al. (2014) French paper about the lock in effect on diversifying crops Consistent and organized action from all stakeholders in the agricultural sector is needed in order to break out of the lock in effect Economic Social Lechenet et al. (2014) Assessment of different cropping systems in France: organic farming is less energy efficient and has lower productivity than agriculture with pesticides, farming with pesticides is less work intensive Economic Environment Colnenne-David and Doré (2015) Analysis of the design of three arable farming systems: (1) no pesticides, but with mineral fertilizer; (2) reduced fossil energy or greenhouse gas emission by 50%; (3) maximizing yields, the systems with pesticide usage have higher yields and better soil health Environment Colnenne-David et al. (2017) Continued analysis of Colnenne-David and Doré (2015) Find that not using pesticides causes lower carbon sequestration due to high usage of tillage (soil health) Economic Carpentier and Reboud (2018) Analyzed a simple choice situation to assess farmers' attitudes toward pest risk Farmers use pesticides in order to achieve high profits when pesticide prices are low Economic Tamm et al. (2018) Scenario analysis: what would happen if Swiss agriculture switched to 100% organic farming In arable farming, 98.5% of pesticides would be waived, but yields would decrease and some crops, such as sugar beet, could not be grown Economic Social Environment Cellier et al. (2018) Evaluation of the Rés0Pest project: the energy efficiency without pesticides is evaluated as low, some farmers complain about the higher work load of farming without pesticides, and frequent tillage is decreasing soil macro fauna Social Schwarz et al. (2018) Long-term experiment of the Julius-Kühn Institute about integrated plant protection Reducing pesticides is possible but needs a high workload; using no pesticides results in high-yield losses Economic Knapp and van der Heijden (2018) Meta-analysis about temporal yield stability Organic yields are less stable than conventional yields, but the gap in yield stability can be decreased by enhanced fertilization Economic Social Environment Moss (2019) Investigates through literature research why farmers are reluctant to waive herbicides: in a box, the reasons are listed, like higher, immediate profitability; however, also risk aversion is mentioned as one reason, another is a lack of information and trained labor Environmental effects such as soil erosion as a consequence of non-chemical weed control Economic Seufert (2019) Literature review that compares organic and conventional farming; states that there is evidence for higher yield stability in conventional farming Social Möhring et al. (2020) Analysis of the relationship between crop insurance and pesticide input; results suggest that without insurance pesticide input would be lower Social Wuepper et al. (2021) Analysis of Swiss fruit farmers; the results suggest that farmers who receive advice from public extension services, are more likely to use preventive measures; farmers who receive advice from private extension services are more likely to use insecticides Economic Kaiser and Burger (2022) Analysis of interviews with farmers and plant protection experts about farmers' usual pesticide usage Identification of reasons why farmers use pesticides and which policies for reduction would be feasible Social Jacquet et al. (2022) Explanation of why a new research paradigm for pesticide-free agriculture is needed and which strategies should be followed Economic Möhring and Finger (2022) Analysis of a new cropping system (no pesticides in wheat production); results suggest that risk-averse farmers are less likely to adopt it  Pimentel et al. (1992) Study from the USA that assesses the direct and indirect costs of pesticide usage There are health risks, threats to biodiversity and food safety, also water quality suffering, and pests developing resistances that cause indirect costs Social Antle and Pingali (1994) Case study from the Philippines shows that pesticides can have negative impact on farmers' health Social Crissman et al. (1994) Analyses of pesticide usage in potato production in Ecuador, which is bad for farmer's health but crucial for potato production, hence there is a tradeoff between both aspects Social Environment de Souza Filho et al. (1999) Study from Brazil about the determining factors that are necessary for farmers to switch to arable farming; farmers are more likely to adopt sustainable agriculture when they have knowledge of the negative effects of pesticides, are part of a farmer's organization, employ family members, or have a farm with good soil Environment Wood et al. (2000) Analysis of global ecosystems; states that pesticides can have a negative impact on the environment Economic Environment Mäder et al. (2002) Report of an experiment that lasted for 21 years and compared organic and conventional agriculture; in organic agriculture, similar yields to conventional farming are possible depending on the crop; profits are similar in both systems; soils in organic agriculture show higher biological activity Economic Social Environment Pimentel et al. (2005) Comparison of different farming types (two organic and one conventional), data from an experiment that lasted over 22 years; yields were similar in all farming systems, but organic farming is more drought resistant and shows lower economic risk and savings in costs, better environmental effects, the results depend on crops, region, and technology Environment Kolbe (2006) Summarizes effects of crop rotations and highlights the importance of diverse crops in order to reduce pesticides Social Environment Economic Sexton (2007) Assessment of effects of pesticide usage, some effects are resistance development of pests toward pesticides, health risks, and loss of biodiversity Environment Bright et al. (2008) Review of negative effects that pesticides have on birds Social Environment Abhilash and Singh (2009) Review of risks (health and environment) due to pesticide application and recommendations to mitigate those in India Economic Bürger and Gerowitt (2009) Analyze pesticide usage in winter wheat and oilseed rape in northeast Germany between 2000 and 2004; they find that pesticide usage can be reduced by applying pesticides less frequently, using fewer mixtures of various pesticides, or using lower application rates Environment Chikowo et al. (2009) Experiment that lasted for 6 years in order to analyze integrated weed management practices and highlights the importance of a wide crop rotation; less environmental impact of integrated weed management Social Pardo et al. (2010) Analysis of the implementation of integrated weed management, which then shows a lower workload  Boussemart et al. (2011) Data from 600 farms in France over a period of 12 years are analyzed in order to estimate the impact of using different amounts of pesticides; reduction in pesticide usage is possible in most cases and would reduce the production cost Economic Jacquet et al. (2011) Study about the effects of decreasing pesticide use in French agriculture: reducing pesticides results in increasing gross margin (moving from high input to medium input farming); pesticides reduction of 10 to 30% is feasible Economic Bürger et al. (2012) Study of data from German wheat fields in 2001-2007 to analyze arable farming measures of integrated pest management; some farmers use integrated pest management in order to save production costs Economic Delbridge et al. (2013) Comparison of profitability of conventional and organic agriculture in the USA Similar yields and high profitability in organic agriculture are possible (highly dependent on management and region) Environment Melander et al. (2013) Review on how agriculture can be less dependent on herbicides, for example, by applying strategies like wide and diverse crop rotations; additionally, innovative measures are introduced, such as thermal control Social Environment Nave et al. (2013) Survey of wheat farmers in France; pesticide usage is high when farmers do not employ family labor and when farmers do not participate in advisory groups; pesticide usage is lower when farmers care for health risks and the environment Economic Social Environment Lechenet et al. (2014) French study that analyses different arable farming systems and their sustainability; using less pesticide results in better water quality, less energy consumption, and cost savings; it does not result in a higher workload and has no impact on profitability or productivity; crop rotations support financial stability through a more diverse rotation Economic Le Bail et al. (2014) Review states that the absence of pesticides for certain crops (minor crops) hinders a transition toward a more diverse rotation Economic Lamichhane et al. (2015) There is a lack of pesticides for minor crops, so-called minor use; one solution to fight pests in minor uses is integrated pest management practices Economic Lechenet et al. (2017) Assessment of data from 946 farms in France shows that high yields are possible with low levels of pesticide use Reduction of 42% is possible without compromising yields, hence, yields similar to conventional farming are feasible Economic Colnenne-David et al. (2017) Four agricultural farming systems are designed and tested in one rotation; one system tests cropping without pesticides The no-pest system shows high gross margins and the same energy use efficiency compared to the other systems success is essentially due to three characteristics of modern farming: the development of cultivars through modifying their genetics, enhanced fertility due to artificial fertilizers and irrigation, and control of diseases, weeds, and insects by means of pesticides (Tilman 1999). These three features were developed to protect the crops from losses and, therefore, increase production (Tilman 1999). Artificial fertilizer and irrigation have yield-increasing effects, while pesticides have mainly yield-securing effects (Claupein 1993). Some pesticides, such as fungicides, also have an indirect yieldincreasing effect (Priestley 1981). Yield increases due to fungicide treatment can be credited not only to disease reduction alone but also to delayed senescence (Priestley 1981). Crop loss is divided into two terms: loss potential is the no-control scenario in which there is no biological, chemical, or physical protection, at the same time, holding all other things (irrigation, crop species, fertilization, etc.) constant, and actual loss, which describes the loss of yield although crop protection measures are in place (Oerke and Dehne 2004). Oerke and Dehne (2004) calculated that from 1996 to 1998, the overall loss potential was approximately 67% worldwide. This is reduced to 32% actual losses of attainable yield due to plant protection measures. The losses vary among cultivars and regions (Oerke and Dehne 2004). Furthermore, crop losses are categorized into quantitative and/or qualitative losses (Oerke 2006). Oerke (2006) describes qualitative losses as characteristics such as reduced content of valued ingredients, increased content of toxic substances, less appealing external appearances, or reduced suitability for storage. Quantitative loss is defined as a yield below the yield potential.
In general, it can be said that farmers depend on pesticides to safeguard their crops from damage caused by insects,  Cellier et al. (2018) Evaluation of the Rés0Pest project shows that farming without pesticides meets farmers' expectations to not handle dangerous products (pesticides) Economic Moss (2019) Review of reasons why farmers do not want to apply integrated weed management practices; an action plan is introduced to improve uptakes of integrated weed management measures Social Environment Sharma et al. (2019) Literature research on pesticide usage in the world, which can harm ecosystems and is a risk to health Environment BMU (Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit) and Bundesamt für Naturschutz (2020) Assessment of the state of nature in Germany; land use change and agricultural intensification are the main drivers for biodiversity loss and decreasing water quality Environment Sud (2020) OECD paper about managing the effects of pesticides and fertilizer and corresponding costs that arise through damage to the environment and human health; policy instruments are reviewed and case studies are presented Environment Chèze et al. (2020) Choice experiment in order to understand why farmers are not switching to decreased pesticide usage Farmers who believe that pesticides are bad for the environment and for their health are more likely to reduce pesticides input Economic Dachbrodt-Saaydeh et al. (2021) Analyzed German farm network, and concluded that there is still potential to reduce pesticide applications, especially for insecticide use Social Jacquet et al. (2022) Explanation of why a new research paradigm for pesticide-free agriculture is needed and which strategies should be followed Environment Möhring and Finger (2022) Analysis of a new cropping system (no pesticides in wheat production); results suggest that farmers who believe the new system is more sustainable are more likely to adopt it weeds, and diseases that reduce yield and crop quality (Lamichhane et al. 2016). Increasing or sustaining profitability is a major reason for using pesticides (see Table 6). However, also positive impacts of nonchemical plant protection measures and reasons why farmers avoid using pesticides are identified (see Table 7 and Fig. 3). There is, for example, evidence that systems without pesticides have beneficial environmental effects, such as increased water quality and higher biodiversity (Sanders and Heß 2019;Stein-Bachinger et al. 2021). Reasons for pesticide use and reasons for their rejection are presented in the following.

Economic reasons
The literature review reveals some more positive effects beyond higher yield and crop quality that give farmers reasons to use pesticides (see Table 6). In their analysis, Carpentier and Reboud (2018) point out that economic factors are determinants of today's levels of pesticide applications. This means, on the one hand, that farmers use pesticides because it is a cheap way to protect their crops and to achieve high profits. On the other hand, farmers would reduce pesticide applications if these pesticides were too costly and accept resulting losses due to insects, weeds, and diseases instead.

Risk aversion
Farmers are considered to behave in a risk-averse manner (Iyer et al. 2020). For farmers, pesticides represent a way to reduce the risk of qualitative or quantitative losses (Kaiser and Burger 2022). Hence, there is a relationship between risk aversion and the usage of pesticides (Carpentier and Reboud 2018). Weather, pests, and diseases, as well as policies and market conditions, determine the production risk (Iyer et al. 2020). Farmers cannot influence most of these risks. Therefore, they protect their yield by using pesticides (Cooper and Dobson 2007). The risk aversion of farmers leads to the assumption that there is an insurance aspect due to which farmers use (i) pesticides at all, (ii) more pesticides than necessary, or (iii) various mixtures of pesticides to insure themselves against higher or extreme yield losses. This means that, in practice, farmers sometimes do not act according to damage thresholds but rather are motivated by securing a certain yield level (Carpentier and Reboud 2018). They have an aversion against increased risk of production losses and believe that high yields cannot be achieved while reducing pesticides (Chèze et al. 2020). In this way, they want to achieve high profits and attain a psychologically comfortable level of crop protection (Carpentier and Reboud 2018;Iyer et al. 2020). This means that farmers are likely to perceive the risk of increased yield losses as a psychological cost, no matter the actual financial outcome (Chèze et al. 2020). Möhring and Finger (2022) suggest that for adopting a new cropping system, such as farming without pesticides, farmers' perception of risk is crucial. If they expect high reductions in yield, then the probability increases that they will not participate in this new cropping system. In this regard, Chèze et al. (2020) advise implementing a production-risk therefore bubbles overlap. Note: economic = articles give reasons for pesticide use that concern the economic situation of the farmer, a country, or in general. Environment = articles give effects or reasons that concern nature. Social = articles treat aspects of pesticide use that concern the general well-being of farmers and society. premium to compensate for the increased risk of yield losses due to pesticide reduction and to secure farmers' income.

The optimal pesticide input level
Testing the hypothesis that farmers behave according to the insurance aspect is not an easy task due to the lack of literature and observation on this subject. For the past 11 years, the German Julius Kühn-Institute (JKI) has been collecting data on the use of crop protection from the network of reference farms for plant protection (Dachbrodt-Saaydeh et al. 2021).
This network contains approximately 90 representative farms in Germany (Dachbrodt-Saaydeh et al. 2021). Germany's National Action Plan (NAP) target to reduce applications of pesticides is the quota of "95% conformity with the necessary-minimum requirement" (Federal Ministry of Food, Agriculture, and Consumer Protection 2013). The "necessary-minimum requirement" describes the amount of pesticides that are necessary to achieve a yield that makes farming economically feasible, given that all alternative Table 4 Detailed literature overview of fertilizer usage and its correlation with pesticides in chronological order. Source: own compilation.

Category
Literature Content Economic Büschbell and Hoffmann (1992) Experiment with the effects of various nitrogen inputs on pathogens in winter wheat; they find that at low N rates, pesticide usage is not economically sensible (low yield) Economic Claupein (1993) Long-term experiment about N fertilization and pesticide input; the results suggest that growth factors have to be combined in optimal amounts in order to reach maximal resource use efficiency; without pesticides, N fertilizer cannot be used in an optimal way by the crops Economic Mäder et al. (2002) Analysis of a 21-year-old experiment that compares cropping systems the results show that lower yields are mainly caused by lower N inputs Economic Olesen et al. (2003a) A total of 3 years of experiments were to investigate the optimal rate of N fertilization and fungicide input timing in winter wheat; estimations show that early-applied N fertilizer increases demand for pest control; furthermore, the optimal fungicide rate increases linearly with applied N fertilizer Economic Olesen et al. (2003b) Same experiment as in Olesen et al. (2003a); the analysis suggests that disease severities of septoria leaf spot and powdery mildew are increased by higher N fertilizer application Social Environment Sheriff (2005) This review shows that farmers oversupply fertilizer due to uncertainty of agricultural production; this over application might have adverse effects on the environment Economic Walters and Bingham (2007) Review on mineral fertilizer that supports diseases in crops; the results show that oversupplying nutrients, especially N can cause severe diseases and reduce yield and quality Economic Social Meyer-Aurich et al. (2009) An analysis of tillage effects and fertilizer use shows that risk aversion is a determinant of high fertilizer input Economic Roberts (2009) Review on the importance of mineral fertilizers in agricultural production; especially cereal yields depend on N fertilizer increasing the crop yield by 30 to 50% Environment Savci (2012) Review of adverse effects of chemical fertilizer on soil, water, and air Economic Social Stewart and Roberts (2012) Analysis of yield gap and how mineral fertilizer can close this gap; the authors stress the importance of mineral fertilizer for world food security Economic Huber et al. (2012) Paper on the interaction of fertilizer and pests; undersupply and oversupply can have adverse effects; it should be aimed at a balanced supply of nutrients Economic Social Environment Lechenet et al. (2014) The authors assess the sustainability of various cropping systems; their results show that cropping systems without pesticides rely less on N fertilization than agriculture with pesticide input due to a more diversified crop rotation Economic Knapp and van der Heijden (2018) Meta-analysis that assesses temporal yield in organic and conventional agriculture; the results show that organic agriculture has lower yield stability, but this stability gap can be reduced by enhanced fertilization Economic Social Meyer-Aurich and Karatay (2019) Analysis of optimal N fertilizer levels and its impact on production risk in wheat production farmers aim at high grain quality and, therefore, increase N input Economic Macholdt et al. (2019) A total of 60 years of experiments on production risk and yield stability; the authors highlight that mineral fertilization is crucial for plants to compensate for environmental stress Economic Zhang et al. (2020) Study on determinants of corn yield; the amount of pesticide input has the biggest impact on corn yield; mineral fertilization is also important but not as crucial as pesticides options for plant protection have been considered and the protection of operators, the environment, and consumers is assured (Federal Ministry of Food, Agriculture, and Consumer Protection 2013). The analyses show that the application of pesticides is determined by regional characteristics of pest occurrence and that the use of pesticides was mostly appropriate and moderate over the past 11 years (Dachbrodt-Saaydeh et al. 2021). In winter wheat, 88% of pesticide applications are within the necessary level; in winter barley, it is 90%; and in winter rapeseed, it is 87% (Dachbrodt-Saaydeh et al. 2021). This means that there is still potential to reduce pesticide applications in these crops, especially for insecticide use (Dachbrodt-Saaydeh et al. 2021).
There are several economic analyses that investigate pesticide use reduction: For example, a French study examines a 50% reduction and zero pesticide application in wheat in comparison with current pesticide input levels (Hossard et al. 2014). Such a reduction is not profitable for farmers, as a yield loss of 5 to 13% is predicted and the subsequent pesticide cost reduction cannot compensate for yield loss at current wheat prices. Zero pesticide application would reduce current yields by 24.3 to 33% (Hossard et al. 2014). These results are supported by an earlier French study, which shows that a pesticide use reduction of 10 to 30% is feasible in arable farming while maintaining profitability, but a reduction of 50% would cause a higher reduction in yield and farmer income (Jacquet et al. 2011). Bürger and Gerowitt (2009) analyze pesticide usage in winter wheat and oilseed rape in Germany. They found that pesticide input can be reduced by applying pesticides less frequently, using fewer mixtures of various pesticides, or using lower application rates.
Another important contribution about reducing pesticides while preserving yields is the work of Lechenet et al. (2017). This study suggests that there is no conflict between the reduced use of pesticides and both high profitability and high productivity in 77% of 946 analyzed farms in France (Lechenet et al. 2017). Lechenet et al. (2017) estimate that the reduction of pesticide usage by 42% has neither a negative impact on profitability nor on productivity in 59% of the farms. This means that farmers did not attain the optimum before the pesticide reduction. In particular, livestock farms that mainly cultivate maize and grassland have the highest potential to reduce pesticide use. However, farms that growinput intensive crops such as potatoes and sugar beets depend on large amounts of pesticides to maintain yields. Other studies, for example, from Nave et al. (2013), support the hypothesis from Lechenet et al. (2017) that a high input of pesticides is not economically reasonable and can be reduced. Nave et al. (2013) show that 33% of the farmers investigated in their study use high amounts of pesticides and receive moderate yields of wheat, while 38% of the farmers use moderate amounts of pesticides and produce high yields. Their network consists of farmers from a French region known for high cereal production. Nave et al. (2013) identify three types of management: high input, moderate input, and low input. In this experiment, the most efficient cropping system is the moderate-input type because it has been observed that this type of farming has higher yields, lower inputs, and a higher gross margin than the other two types (Nave et al. 2013).

Resource efficiency
The study by Deike et al. (2008) aimed to evaluate the productivity and environmental effects of different cropping systems. The trials included variations in crop rotation systems and cropping management. The results show that the type of crops the rotation consists of is important for yield, sustainability, and management decisions. However, an interaction between pesticide use intensity and crop rotation could not be confirmed (Deike et al. 2008). Deike et al. (2008) demonstrate that pesticide usage, which is situation-related will increase yield. In addition, the efficiency of energy and nitrogen use is improved. Pesticide use that follows guidelines of integrated pest management (IPM) has a low-risk potential for the environment, and this risk is reduced by a further decrease in pesticide input. This study highlights that a diversified crop rotation has the potential for decreased pesticide and fertilizer usage or reduced intensity of tillage without compromising the overall production capacity.
Several other scholars that examine low-or zero-pesticide systems report higher energy consumption in those low-input systems. Lechenet et al. (2014) compare organic, integrated, and conventional agriculture and find that organic systems are not as productive and not as energy efficient as the other systems. Moreover, it may not be profitable: zero-pesticide systems have no pesticide costs but increased costs due to mechanical weeding, which is necessary for a cropping system without herbicides. The savings from pesticide cost reduction cannot compensate for these costs, in addition to reduced productivity.
In contrast, several authors have argued that low-or zero-pesticide systems have economic benefits. Boussemart et al. (2011) concentrated on the costs of cropping systems and showed that extensive agriculture is more cost-effective than intensive agriculture. Boussemart et al. (2011) evaluate farms in France and their inputs (e.g., seeds, fertilizers, and pesticides) to compare their current situation with converting to extensive or intensive agriculture. Costs can be reduced by 25.4% if farmers adopt agricultural extensification practices and by 13.1% if they convert to agricultural intensification. In regard to pesticide input, potential reductions can be up to 29% of the current situation.

Comparison of yields
In general, organic yields can be similar to conventional yields, depending on the type of cultivar, soil, and weather (Pimentel et al. 2005). Mäder et al. (2002) present the Table 6 Categorization of the literature on the usage of pesticides. Definitions: High yield: produces higher yield compared to other cropping systems. High profitability: gains more profit than other cropping systems. High crop quality: the quality of crops is increased. Higher (energy) efficiency: factors of production are used in a more efficient way (less energy is needed to perform the same task). Risk aversion, psychological costs, and yield stability: risk-averse farmers prefer outcomes with low uncertainty. They can reduce the risk by using pesticides and stabilize their yield. They perceive psychological costs when there is high pest pressure, while they cannot reduce the risk with pesticides. Lock in effect: describes the situation when a farmer has chosen a certain cropping system in the past and cannot convert to another cropping system without substantial costs or inconvenience. The lockin effect comprises other reasons, such as high-yielding varieties: crops bred for high yields are more susceptible to pests and can hardly be grown without pesticides. Lack of trained labor and equipment: conven-tional farming is prevalent, and equipment for plant protection without pesticides and labor that is trained to handle this equipment is scarce. Ignorance/lack of information: farmers are not informed about alternative cropping systems. Recommended practice: extension services and sales representatives recommend practices with pesticides. Administrative burden: converting to another cropping system can be accompanied by increased controls and administration to verify compliance. Simplicity, convenience of using pesticides, and lower workload: applying pesticides is accompanied by easier work tasks and a lower workload. Crop insurance: gives an incentive to grow more pesticide intensive-crops. Food security: conventional farming is more suitable to fight food insecurity. Food safety: applying pesticides enhances crop quality and fights pests that might harm consumers. Low greenhouse gas emissions: systems that use pesticides emit less greenhouse gas emissions. Pesticides are better for soil health: farming without pesticides relies on tillage, which might decrease soil health. Source: own compilation.

Category
Reason results from a trial that lasted for 21 years and compared conventional and organic cropping systems. The authors show that potato yields of organic systems are approximately 58 to 66% lower, winter wheat yields are reduced by approximately 10%, and grass-clover yields have only marginal differences compared to conventional farming. However, organic cash crops cannot be cultivated as often as conventional cash crops due to the need for a more diverse crop rotation (Pimentel et al. 2005). Cellier et al.
(2018) evaluated a cropping system similar to MECS, which also uses mineral fertilizer but lacks pesticides. They conclude that yields of the zero-pesticide systems are lower than conventional yields but not as low as expected and higher than yields in organic agriculture. Nevertheless, profitability suffers due to high seed and mechanization costs.

Yield stability
High yields and stable yields over time are important for farmers (at least as long as farmers are risk averse); however, there are only a few studies that compare the temporal yield stability of organic and conventional cropping systems (Seufert 2019). To our knowledge, there is no literature about Table 7 Categorization of the literature on the rejection of pesticide usage. Definitions: Savings in production cost and energy: waiving pesticides reduces costs for chemical plant protection and energy input. Lower economic risks: renouncing pesticides lowers the economic risk due to alternative farming practices. Similar yield: farming without pesticides can produce similar yields as farming with pesticides. High profitability: farming without pesticides gains more profit. Pests develop resistance: pests can develop resistances toward pesticides. Crop resistance: new cultivars can obtain resistance toward pests due to breeding, which makes pesticides unnecessary. Minor uses: some crops are not cultivated much; therefore, the financial incentive for pesticide industries is missing to produce pesticides for these crops. Workload: waiving pesticides is accompanied by a workload that is evenly spread over the year. Health risks: applying pesticides might be toxic to producers. Food safety: consuming food that is grown with pesticides might be toxic. Caring for future generations: farmers, who have families and children, care more about the future and reject pesticides due to their possible negative effects. Knowledge: farmers, who rely upon an extension service know more about pesticides and therefore reject pesticides. Biodiversity, protection of animals (bees, birds, and fishes), beneficial microorganisms, and invertebrates: pesticides can cause harm to the environment; therefore, pesticides might be rejected. Soil organic matter: pesticides might have negative effects on soil organic matter. Water quality: pesticides can leach from the soil and reduce water quality. Crop rotation: a wide and diverse crop rotation is a prerequisite for farming without pesticides. Source: own compilation.  (2019) reviews the literature about organic versus conventional yield stability over time. She concludes that there is some evidence for higher temporal yield stability in conventional farming and some evidence that there is no difference between the cropping systems. There is little evidence for higher yield stability over time in organic cropping systems. Knapp and van der Heijden (2018) also analyzed the temporal yield stability of various cropping systems in a meta-analysis based on 193 studies. They concluded that organic cropping systems have lower temporal yield stability than conventional agriculture. Nevertheless, this yield stability gap between organic and conventional cropping systems can be reduced by enhanced fertilization.

Resistance to pesticides
Furthermore, nonchemical measures against pests are frequently adopted to compensate for the inefficiencies of pesticides (Moss 2019). Pests develop resistance to certain pesticides, which is why these protection measures are no longer as effective and there is an absence of new pesticides that serve as substitutes for the old ones (Moss 2019;Pimentel et al. 1992;Sexton 2007). Oerke and Dehne (2004) argue that crop losses increase over time, despite the increased use of pesticides. However, according to these authors, resistance that pests develop against pesticides contributes only little to this phenomenon. Changes in farming practices, for instance, less diverse crop rotations, increased monocropping, and the use of high-yielding varieties that are susceptible to diseases, are mainly responsible for increased crop losses. In contrast, for reduced fungicide treatment, Jahn et al. (2010) find that the resistance characteristics of crop varieties are a decisive factor in the need for control. Especially for winter rye and winter barley, due to the low level of resistance to the dominant diseases, at least one fungicide application was required in all years of their trial (11 years).

Minor uses
Another reason why farmers do not use pesticides is that there are no pesticides available for certain crops due to their low scope of application (so-called minor uses) (Lamichhane et al. 2015). This is because of the low economic value of the corresponding crops and the costly risk assessment needed for official approval of the pesticides (Lamichhane et al. 2015;Le Bail et al. 2014). This means that some pesticides are not available on the market, although these pesticides would be important for farmers to protect their crops (Lamichhane et al. 2015). Therefore, nonchemical plant protection or IPM solutions are crucial in these cases to substitute for nonexistent pesticides (Lamichhane et al. 2015).

Social reasons
Defining the social dimension in agriculture is not an easy task (Janker and Mann 2020). In this work, social reasons for using pesticides or rejecting their usage are any factors that consider human health, well-being, and quality of life. This includes topics on a global scale that have an impact on society, such as food security, as well as on a personal scale, such as workload.

Lock in effect
One widely discussed reason why farmers reject converting to a cropping system with reduced or without pesticides is Fig. 3 Overview of the effects of a mineral ecological cropping system. Note: Circles = instruments of a mineral ecological cropping system; rectangles = objectives; "+" or "−" = strong or well-established positive or negative effects; "+/−" = ambiguous effect. Source: own compilation.
the so-called lock-in effect: farmers are locked in conventional farming because it is their initial farming practice. Changing it to another system is costly and requires all actors in the agricultural sector to change. This problem has been observed by several scholars (see Table 6). Since the 1960s, the agricultural sector (plant breeders, researchers, extension services, etc.) developed intensive farming strategies to increase yield (Lamine et al. 2010). This means that farmers, who want to switch to zero pesticide usage face several obstacles, such as extension services exclusively recommending conventional practices (Moss 2019;Nave et al. 2013). This leads to a lack of knowledge or to ignorance about the unsustainability of pesticides. Nave et al. (2013) find that acquiring information through extension groups encourages pesticide use reduction. Furthermore, Wuepper et al. (2021) suggest that the type of extension service also matters for adopting alternative crop protection. Farmers who work with private extension services are more likely to use pesticides. Farmers who receive advice from public extension services will probably adopt preventive measures. Additionally, farmers can experience a lack of crop seeds that are resistant to pests because in recent years only crops were cultivated suitable to achieve high yields (Lamine et al. 2010). These high-yielding cultivars are more susceptible to diseases and dependent on pesticides (Wilson and Tisdell 2001). Another issue is the availability of employees who are trained to use nonchemical measures and the right equipment for low pesticide measures, which is not always given (Lamine et al. 2010;Meissle et al. 2010;Moss 2019). Chèze et al. (2020) find that farmers often oppose the administrative commitments that may come along with low-or zero-pesticide measures. In this context, contracts and certification processes with public authorities that ensure farmers' compliance with zero or reduced pesticide usage are considered a burden and less of a chance to integrate into a network or receive support. Furthermore, a development period where farmers learn how to handle the innovative farming system can occur (Cellier et al. 2018). During this time, high pest and weed pressure are likely (Cellier et al. 2018). Therefore, Jacquet et al. (2022) recommend compensating farmers in this transition period. Furthermore, crop insurance and pesticide use can have a positive or negative relationship (Möhring et al. 2020). Möhring et al. (2020) find that crop insurance leads to higher pesticide use because insurance gives the incentive to use more pesticide-intensive crops. Their results suggest that pesticide input would be reduced by 6 to 11% without crop insurance.

More work, but better distributed?
One reason for using pesticides may be the convenience of using them: nonchemical solutions for crop protection often exist for many cultivars, but their implementation is more complex (Le Bail et al. 2014). Moss (2019) calls this the inconvenience factor. Higher complexity and time-consuming tasks of nonchemical plant protection are mainly caused by a more diversified crop rotation and increased monitoring of the fields, which are prerequisites for reduced or zero pesticide application (Lechenet et al. 2014). Hence, pesticide usage reduces the workload of farmers (Cellier et al. 2018;Schwarz et al. 2018). On the other hand, Pardo et al. (2010) find for zero herbicide systems that the working hours are better distributed over the year so that there is no peak time in labor. This finding is supported by several scholars who argue that the work is allocated more evenly over the year in the case of a more diverse crop rotation (Lechenet et al. 2014;Pardo et al. 2010;Pimentel et al. 2005).

Food security
Food security is an important aspect of agricultural production because of the increasing world population that demands higher yields in the future (Sexton 2007). Therefore, some authors advocate high-yielding conventional farming to achieve worldwide food security (Cooper and Dobson 2007;Noleppa and von Witzke 2013). Noleppa and von Witzke (2013) highlight that although Germany is a comparatively small country, a complete conversion to organic farming can change the entire food supply and threaten food security. Immense harvest losses would occur due to the absence of modern crop protection and fertilizers. These losses are to be expected for potatoes (minus 44% yield), maize (minus 51% yield), and wheat (minus 54% yield) when compared to the yields of conventional agriculture in Germany (Noleppa and von Witzke 2013).

Risk for consumers and producers
Various reasons for rejecting pesticides can also be found in the literature: One study discusses the exposure of consumers to pesticides via food and water (Pimentel et al. 1992). This can be an argument for rejecting pesticides. In contrast, Cooper and Dobson (2007) mention higher food safety through pesticides due to reduced fungal toxins. Although pesticide residues in food often occur, in most cases the maximum levels allowed are observed and food is classified as safe (European Food Safety Authority et al. 2020). Sharma et al. (2019) note that pesticides are harmful to organisms. Farmers who do not apply pesticides appropriately are exposed to health risks (Abhilash and Singh 2009). Being aware of these risks leads to reduced usage of pesticides (Nave et al. 2013). Systems with zero pesticide applications meet farmers' expectations of not handling dangerous products (Cellier et al. 2018).
Other social factors and reasons for rejecting pesticide inputs are investigated by Nave et al. (2013), who conduct an analysis that shows why farmers reduce chemical inputs. The authors interviewed 71 farmers in France who grow winter wheat. Farmers often implement low-input practices when they have a family or own the land they are farming because they care more about the environment and the future. As mentioned before, taking part in extension groups and having access to various information sources encourages lowinput agriculture. These findings are supported by de Souza Filho et al. (1999) and Lamine et al. (2010). Moss (2019) reports that farmers may reject alternative plant protection measures because they fear that they have a negative impact on the environment. Indeed, Noleppa and von Witzke (2013) argue that pesticides emit only a few greenhouse gases, but conversion to a farming system without pesticides would cause an increase in greenhouse gas emissions due to decreased yields that need to be compensated by converting forests into farmland. In addition, waiving pesticides reduces soil organic matter because plowing needs to be done more often. This is supported by findings from two other studies (Cellier et al. 2018;Colnenne-David and Doré 2015). Pimentel et al. (2005) compare conventional and organic farming and disagree with this statement. They find higher soil organic matter in systems without chemical input instead. This is supported by Mäder et al. (2002), who also compared organic and conventional cropping systems. They conclude that organic agriculture results in enhanced soil fertility and biodiversity.

The importance of crop rotation and innovation
As mentioned before, crop diversification is a prerequisite for low-or zero-pesticide farming (Lechenet et al. 2014). A wider crop rotation increases biodiversity, decreases incidences of pests, and therefore reduces pesticide input and negative impacts on the environment (Lechenet et al. 2014). Using a more diversified crop rotation and cover crops also has the benefit of reducing soil erosion (Pimentel et al. 2005). Kolbe (2006) also recognized that unfavorable crop rotations promote weeds, diseases, and pests, which have an impact on crop yield and quality. This affects especially organic and lowinput agriculture. Therefore, Kolbe (2006) further develops crop sequences that help to decrease dependence on pesticides.
Conventional crop production relies heavily on the usage of herbicides (Melander et al. 2013). Among the different pesticide categories (herbicide, fungicide, and insecticide), herbicide reduction has the highest risk of causing yield losses (Lechenet et al. 2017). Efforts are being made to reduce the dependency on herbicides, for example, with the help of integrated weed management (IWM) (Chikowo et al. 2009). IWM strategies mainly use mechanical weed control and only partly apply herbicides (Chikowo et al. 2009). Chikowo et al. (2009) examine IWM measures and find that they can control weeds in the long term and that the environmental impact can be reduced while mostly maintaining yields. Nevertheless, IWM practices such as mechanical weed control and false seedbed preparation increase complexity and workload. Melander et al. (2013) stress the importance of reducing weeds with nonchemical measures by means of crop rotations and innovations, such as thermal control or intercropping. However, more research is necessary on these innovative methods.

Adverse effects on the environment
Pesticides can be a problem for ecosystems because they harm not only weeds, insects, and pests but also other organisms that are not targeted (Sharma et al. 2019). In the report of the BMU, it is concluded that the state of essential parts of biodiversity in Germany is critical (BMU 2020). Many habitats and species have an unfavorable-inadequate or poor state of preservation. In addition, for approximately onethird of the brood bird species the populations decreased in recent years. The main causes of this development are, among others, high nutrient and pesticide inputs, intensification or abandonment of land use, including the abandonment of traditional land use forms, changes in the hydrology and morphology of water bodies, drainage, and groundwater extraction. Sud (2020), Wood et al. (2000), and Abhilash and Singh (2009) report similar negative effects on land and water organisms due to pesticides in many other developed and developing countries. In contrast, agriculture with low or zero pesticide usage has a low impact on water and soil quality (Lechenet et al. 2014). According to Möhring and Finger (2022), the environmental benefits of a cropping system are important for farmers. These authors find that farmers who believe that a new cropping system without pesticides is more environmentally friendly are more likely to participate in this system.

The importance of mineral fertilizer and its interaction with plant pests
An interesting topic is the use of mineral fertilizers in relation to plant pests and countering pesticides, as mineral fertilizers are allowed in MECS whereas pesticides are forbidden. Both mineral fertilizers and pesticides are determinants of high-input cropping systems (Fess et al. 2011). The review about the development of mineral fertilizers by Russel and Williams (1977) shows that organic and mineral fertilizers have been used by humans for centuries. Modern fertilizer production started in 1840 with the invention of superphosphate (Russel and Williams 1977). During the green revolution from 1950 on, artificial fertilizers and pesticides simultaneously contributed to the tremendous increase in crop production (Tilman 1999). Since then, the effects of mineral fertilizer on yield, risk perception of farmers, and optimal fertilizer input have been widely discussed by scientists. Whereas the average yield-increasing effect of mineral fertilizer is undisputed, the interaction between the resulting nutrient supply and plant diseases is far from clear-cut, as the effect of additional nutrient supply on disease incidence depends on both the overall level of nutrient supply and the corresponding pathogen. In the case of nitrogen, this can lead to a U-shaped relationship between fertilization and disease incidence (for an illustration and discussion of this relationship along with literature references from crop sciences, see Huber et al. 2012 p.284f.). On the one hand, there are clearly positive correlations between nitrogen (N) supply and, e.g., the incidence of certain obligate biotrophic fungal parasites such as powdery mildew (Erysiphe graminis), which calls for increased fungicide use at higher N fertilization levels. On the other hand, for other (facultative) parasites and at relatively low N supply levels, this correlation was found to be negative, as in the case of leaf spot diseases (Alternaria ssp.). In this context, Huber et al. (2012) state that "[u]sually, a "balanced" nutrient supply that ensures optimal plant growth is also optimal for plant resistance" and that "[…] plants suffering from nutrient deficiency have lower tolerance to diseases and pests, and tolerance can be increased by supplying the deficient nutrient". A plant being undersupplied is more susceptible to certain diseases caused by necrotrophic pathogens. For biotrophic pathogens, undersupplied plants are less "interesting" because there is less to feed upon.
As a MECS aims at a spatially and temporally balanced supply of nitrogen, rather low nutrient inputs should be avoided as they result in reduced yields. We emphasize in our review the positive correlation between nutrient supply and incidences of certain plant diseases at higher nutrient levels.
Contemporary organic agriculture is a cropping system that forbids the application of pesticides and mineral fertilizers (Connor 2018). Mineral fertilizers are an important component of crop yield and quality (Stewart and Roberts 2012). Nevertheless, mineral fertilizer can damage the environment when farmers apply it to fields in an inappropriate way (Savci 2012;Sheriff 2005). For example, this can lead to eutrophication (Rockström et al. 2009). There are also sources that suggest that farmers may overapply fertilizer to reduce risk (Meyer-Aurich et al. 2009;Meyer-Aurich and Karatay 2019). In organic agricultural systems, N can only be added to the system by intercropping leguminous plants or by fertilization with manure, which leads to lower yields compared to fertilization with mineral fertilizer (Connor 2018). Mineral fertilizers increase crop yield by 30 to 50%; especially cereal yields depend on fertilizer applications (Roberts 2009). This is one reason why organic agriculture is criticized as unfit to feed the world's population in the future (Connor 2018).
The application of artificial fertilizers is important to mitigate the uncertainty of crop production (Sheriff 2005). The production-increasing effects are shown by a study by Macholdt et al. (2019), who present an experiment that lasted over 60 years. They analyze the production risk, risk development, and stability of crop yields fertilized with different combinations and amounts of NPK (nitrogen, phosphorus, and potassium) and manure. They find that yield stability and production risk are mainly impacted by climate, followed by added NPK fertilizer and manure fertilization. Sufficient N availability helps crops to compensate for environmental stress, which contributes to yield stability. High levels of mineral fertilizer (NPK) contribute to high yield and stability, resulting in lower production risk when compared to lower fertilization levels (i.e., 50% less or no fertilizer). This is also supported by a study by Knapp and van der Heijden (2018).
Another long-term experiment by Mäder et al. (2002) compares yields of conventional and organic cropping systems. The authors show that the yield of organic wheat and other cereals are reduced by 30 to 50%. It is assumed that lower yields are mainly caused by lower N inputs. The NPK level of the organic systems was between 34 and 51% lower than that of the conventional system. The trials by Macholdt et al. (2019) and Mäder et al. (2002) demonstrate the importance of healthy plants due to mineral fertilizer for high and stable yields. However, the interaction between pests and plant nutrition is complex and differs among plant types, the growing stage of the plant, and pathogen species (Walters and Bingham 2007). There is evidence that oversupplying nutrients, especially N, can cause severe diseases and reduce yield and quality (Walters and Bingham 2007). Therefore, balanced fertilization based on the needs of the plants is crucial (Walters and Bingham 2007).
The relationship between pesticides and mineral fertilizers is of particular relevance regarding MECS. Both mineral fertilizers and pesticides have an important role in high and stable yields (Zhang et al. 2020). Organic cropping systems rely less on nitrogen fertilization than agriculture with pesticide input (Lechenet et al. 2014). This is due to lower yield targets of organic agriculture and a more diversified crop rotation, which incorporates crops such as legumes that are less reliant on nitrogen input (Lechenet et al. 2014). At higher nutrient supply and yield levels, there is a correlation between fertilizer application and certain plant diseases, which may lead to increased pesticide usage. That would mean if farmers use artificial fertilizers, then they also use more pesticides because of the increased need for plant protection at higher cropping intensities (also involving high-yielding varieties and straw-shortening growth regulators).
There is further evidence in the literature for a positive correlation between nutrient supply and pesticide use also because of the higher crop value at stake when the targeted yield levels are greater. Thus, the optimal pesticide doses depend not only on the amount of fertilizer applied to the crops but also on the prices of fertilizer and the revenue a crop yields: Büschbell and Hoffmann (1992) analyze the effect of different N supplies (40, 80, and 160 kg N/ha) on diseases in wheat in two successive years. They stress that the relationship between potential yield and the number of fungicide treatments is important. At low N supply (40 kg N/ha), the yield is so low that it does not make economical sense to apply fungicides. Fungicide usage is economically reasonable at higher N rates of 80 kg N/ha. In particular, the spread of powdery mildew increases with the increasing N rates that are applied. This is supported by Olesen et al. (2003b), who performe a similar analysis on N supply in crops and its effects on diseases. They find that the disease severities of septoria leaf spot and powdery mildew are increased by higher N fertilizer applications. Furthermore, Olesen et al. (2003a) find that the optimal fungicide level increases nearly linearly with the N fertilizer rate that is applied. The optimal amount of fungicide and N level is defined as those doses that give the highest economic return. Hence, the optimal fungicide dose also depends on crop prices. The authors point out that there is an interaction between the amount and timing of N application on the optimal fungicide dose. Early-applied N fertilizer causes a higher need for pesticides but also a higher yield. This is supported by Claupein (1993), who suspects that there is an interaction between N fertilization and pesticides. If so, pesticides can be reduced by decreased N application. In contrast, waving pesticides means that crops may not make optimal use of N fertilization due to diminished N uptake and increased incidences of certain plant diseases.

Conclusion
Agricultural systems, such as organic agriculture, are criticized for not being able to feed a growing world population. Conversely, conventional farming is criticized for causing environmental problems, and this literature research shows that negative impacts on the environment are well documented. Therefore, a hybrid system, MECS, is proposed. This innovative system rejects pesticides to avoid environmental damage. However, mineral fertilizers are permitted to achieve high yields. It is important that farmers accept this new farming system so that it can eventually be put into practice. Therefore, in this literature review, among others, we summarize the reasons why some farmers use pesticides and why others reject them. In this way, the determinants of pesticide use are identified, and important insights are drawn from the reviewed studies that may be important for MECS. Thus, our initially presented research questions are answered in the following: (1) What are the main reasons that determine pesticide usage?
In particular, economic aspects, such as the profitability of a cropping system, are important for farmers' decisions to continue with current farming practices or to convert to a zero-pesticide system. In addition, environmental aspects can be crucial. Research in the literature shows that pesticide use can be reduced without compromising yield and profitability. However, no consensus among scholars can be identified to what extent a pesticide reduction is feasible without prohibitive farm losses. It can be assumed that the feasible reduction depends on regional (climate and soilrelated) conditions and management practices. Additionally, farmers may want to assure stable yields over time and, therefore, apply pesticides as insurance against yield losses and not according to damage thresholds. However, there is little empirical evidence to verify this assumption. In contrast, according to Dachbrodt-Saaydeh et al. (2021), most pesticide applications from 2007 to 2017 corresponded to the necessary level, and only a few pesticide applications were unnecessary.
The literature review suggests that the reasons for pesticide use are manifold and not only related to high yield and profits. The lock-in effect, for example, is an important and complex issue that hinders farmers from converting to low-input agriculture. Furthermore, the MECS will change conventional farming practices. A wider crop rotation, for instance, can partly compensate for renouncing pesticides. There are guidelines for favorable crop sequences (see Section 3.3.1). However, there is also contradictory evidence regarding how much a wider crop rotation increases workload and complexity. Weeds are particularly problematic for many crops. Therefore, herbicide applications may be quite important to prevent yield losses and maintain quality.
For MECS, an increase in soil fertility and biodiversity can be expected compared to conventional farming. This could be a convincing reason for environmentally sensitive farmers to change their farming practices.
(2) How important are mineral fertilizers for high and stable yields, and is there a correlation between fertilizer use and pesticide input?
Mineral fertilizers are important for high and stable yields, but using a dose that is too large can cause harm to the environment and facilitate plant diseases. The literature suggests that cropping systems without pesticides are less dependent on nitrogen fertilization due to a more diversified crop rotation and lower yield targets. Nave et al. (2013) and Kavita et al. (2018) show that high yields can be achieved with increased fertilizer input without increasing pesticide usage. Nevertheless, the literature also shows that without pesticides, N fertilizer cannot be used in an optimal way by crops. There seems to be a correlation between the usage of pesticides and fertilizer. Consequently, in MECS, a balanced supply of nitrogen (both spatially and temporally) should be aimed. This would mean that mineral fertilizers should be applied at lower levels than in conventional farming. Lower nitrogen application is, after all, coupled with the predicted reduced yield. In the future, it will be necessary to perform further research on pest effects at high nitrogen applications in the MECS.
Furthermore, there are several known problems posed by mineral fertilizers that should be considered when designing a MECS. First, the most important nutrients for crops (i.e., NPK) are not produced in a sustainable way. They are either mined (P and K) or produced via the Haber-Bosch process (N), which is extremely energy intensive. Second, phosphate sources will be depleted sooner or later (Gilbert 2009). However, innovative recycling processes could solve these problems by recovering nutrients from sewage and producing mineral fertilizers out of these recovered nutrients. This technique and farmers' attitude toward such recycling are already being researched (Utai et al. 2022).
(3) What are the main recommendations that can be distilled from the literature to design the MECS?
The lessons learned from this review will help to progress toward an innovative and sustainable cropping system. For MECS, we presume that the yields are lower than conventional yields, but not as low as expected, and higher than yields in organic agriculture. A more diverse crop rotation is an important measure to reduce the overall yield variance in cropping systems without pesticides. Therefore, rotations will be more diverse in the MECS than in conventional farming. However, profitability suffers due to high costs for seeds and mechanization and, simultaneously, because of reduced options to fight pests. Therefore, it is recommended to initially compensate farmers who want to switch to the MECS. In addition, increased energy consumption and less net carbon sequestration might occur. There are controversial claims from scholars investigating workload in low-and zero-pesticide systems. To our knowledge, there is no literature that analyzes yield stability over time in a cropping system with mineral fertilizer but without pesticides. However, it can be assumed that the temporal yield stability in the MECS might be higher than that in organic cropping systems due to mineral fertilizer input but lower than that in conventional farming due to the lack of pesticides. Thus, there is a need for innovations in cultivars that are resistant to dominant diseases or for technical innovations that allow for mechanical control methods.
In the future, more research should be done to assess how the abandonment of pesticides affects systems of rationally acting farmers. To analyze profitability and risk aspects, future research should also rely upon mathematical programming models to compare total contribution margins and their variances for different cropping systems. Apart from that, questions arise, such as how will the whole agricultural system change if minimal or zero doses of pesticides are applied in the future? From the example of "minor uses," we can see that it is not economically reasonable for industries to sell small amounts of seldomly used pesticides. Furthermore, the question arises of which crop shares will decrease when there are no pesticides available. Remarkably, there is no consensus among scholars on whether reduced or zero pesticide practices are more labor-intensive. Therefore, it will be interesting to compare the workload that is necessary for MECS and for other cropping systems. Finally, the crop-and site-specific conditions under which (a positive or negative) correlation between fertilizer application and pesticide usage is relevant need to be further investigated in future studies.
Authors' contributions I. Pergner: Conceptualization, investigation, formal analysis, methodology, writing-original draft, and writingreview and editing. C. Lippert: Conceptualization, supervision, writing-review and editing. Data availability All data generated or analyzed during this study are included in this published article (and its supplementary information files).
Materials availability All data generated or analyzed during this study are included in this published article (and its supplementary information files).
Code availability Not applicable.

Declarations
Ethics approval Not applicable.

Conflict of interest The authors declare no competing interests.
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