**2. Material and Methods**

For ethical reasons, low-input industrial crop cultivation on marginal agricultural lands is to be preferred in order to reduce competition for agricultural land use with both food crop cultivation and biodiversity conservation [9,27–30]. As favorable agricultural lands should primarily be used for food crop cultivation, this study focuses on the use of marginal agricultural lands for low-input industrial crop cultivation. Consequently, it aimed at:


To address the above-mentioned research objectives, a thorough literature review was conducted using the search engines of SCOPUS (Elsevier, B.V.) and Google Scholar (Google LLC.). The pre-selection of the industrial crops (Table 1) which was based on a multi-criteria analysis (among others, the maturity of knowledge on industrial crops on marginal land and crops' productivity on marginal land) did not form part of this study. Instead, the study deals with the further evaluation of the growth suitability of 19 promising industrial crops (Table 1), and thus how they meet the requirements for successful development of MALLIS.

**Table 1.** Overview of physiological and technical characteristics of the industrial crops.


The following sub-sections present the concepts underlying the key elements of this study. These key elements are (i) the identification of marginal agro-ecological zones (M-AEZ), (ii) the determination of the growth suitability of the pre-selected industrial crops in the prevailing M-AEZ, and (iii) the development of MALLIS for industrial crop cultivation.

### *2.1. The Identification of Marginal Agro-Ecological Zones (M-AEZ)*

To achieve the first two key elements, mapping was performed as follows: Marginal agricultural lands were mapped [31] according to the biophysical limitations defined and classified by JRC [20–22]. The mapping was limited to a so-called 'agricultural mask'. This mask includes all land that was classified in an agricultural land cover class in at least one of the four Corine Land Cover (CLC) versions (1990, 2000, 2006, and 2012). Further details of the methodological approaches are provided in the following sub-sections.

### *2.2. Determination of the Growth Suitability of the Pre-Selected Industrial Crops in the Prevailing M-AEZ*

The approach to mapping the growth suitability of the 19 pre-selected crops involves the identification of the minimum and maximum climate and soil requirements per crop. The growth suitability requirements of the selected industrial crops were determined according to the literature [32,33]. They were used to map and calculate both the distribution and size of the crop-specific growth suitability areas across European marginal agricultural land. The thresholds for the suitability parameters were set as the starting point at which the crop can grow and survive. The suitable area is, thus, given as the area where all suitability factors are within the minimum and maximum range. In this mapping assessment, a distinction was made between suitable and unsuitable area per crop. However, no further classification of the suitable area was made, for example, into high to low suitability. For an easier interpretation of the results, the European land surface was divided into the three agro-ecological zones (AEZ): Mediterranean (AEZ1), Atlantic (AEZ2) and Continental and Boreal (AEZ3) (Figure 3, Table 2). Each combination of an AEZ with at least one biophysical constraint (Table A1) refers to as 'M-AEZ' (Table 2).

**Figure 3.** Distribution of agro-ecological zones (AEZ) taken into consideration for the development of marginal agricultural land low-input systems (MALLIS) for industrial crops across Europe (modified from Reference [34]).

The basic crop-specific biophysical growth requirements were compiled according to Ramirez-Almeyda et al. (2017) [32]. Each biophysical parameter was divided into a number of classes. For instance, the parameter "precipitation" was divided into eight classes (in mm a<sup>−</sup>1): 0–100,

100–200, 200–300, 300–400, 400–500, 500–600, 600–800, and 800–1000 (Table A2). Afterwards, the growth suitability of each crop was ranked according to these classes based on available literature. Additionally, the basic climatic growth requirements of the crops were compiled (Table 3).



a CH: Salinity or sodicity; CL: Low temperature, high temperature or dryness; FE: Acidity, alkalinity or soil organic matter; RT: Shallow rooting depth or unfavorable texture; TR: Steep slope; WT: Limited soil drainage or excess soil moisture.

a



Accumulated mean daily temperature equal to or above than the crop-specific base temperature.

When mapping the crop-specific growth suitability areas, we only considered whether a crop could potentially grow. We did not take di fferent yield levels into account. In the constraint-specific ranking, classes 0 and 1 were denoted as not suitable. Therefore, if any of the basic climatic growth requirements are not met or any of the constraint-specific rankings falls within class 0 or 1, the area is designated as 'not suitable'. The result was an overview of the potential growth suitability of the pre-selected industrial crops across European marginal agricultural land. This means that only agricultural areas were considered; woodlands and urban areas were excluded from the mapping of marginal agricultural land.

### *2.3. Definition and Methodology of Marginal Land Low-Input Systems (MALLIS) Development for Industrial Crops*

In this sub-section, the definition of best-practice low-input managemen<sup>t</sup> systems for the pre-selected industrial crops (Table 1) is elaborated. This ties in with current knowledge on best low-input agricultural practices for food crop production on good soils [6]. The concept of best-practice low-input agricultural cropping systems considers managemen<sup>t</sup> approaches from many categories of agricultural production, including organic, integrated, conservation agriculture and mixed crop-livestock farming [35–37]. These all have one constant: Low-input agricultural practices seek to optimize the use of on-farm resources while minimizing o ff-farm resources [6,35,36]. This leads to a more 'closed' cycle of production (and less external inputs) [37]. Note, that this more closed production cycle requires both more advanced agronomic skills [38,39] and additional links within the value chain, such as application of biochar [40–49] or phosphate salt recovery from the digestates [50,51]. Therefore, practical guidelines for industrial crops are also under development within the MAGIC project.

Agronomic strategies for the successful application of low-input agricultural practices in a crop managemen<sup>t</sup> system should be seen as a set of strategies that take into consideration both the interactions between plants, soil, the atmosphere and the e fficient use of inputs to enable the highest output with minimal (on-farm and/or o ff-farm) input supply [6,52–54]. Agronomic strategies for low-input systems may also match good agricultural practices—cultivation practices that address economic, social and environmental sustainability [37] for high-quality food and non-food agricultural

products [38,55]. Such practices include the implementation of appropriate crop rotations, pasture management, manure application, soil managemen<sup>t</sup> that maintains or improves soil organic matter, and other land-use practices, as well as conservation tillage practices [8,37,48].

Diversity in crop rotations is a way to reduce reliance on synthetic chemicals, control weeds and pests, maintain soil fertility and reduce soil erosion, prevent soil-borne diseases, leading to the reduction of o ff-farm inputs [54]. Reduced soil tillage is a way to reduce soil erosion, improve water bu ffer capacity, and increase both soil fertility and organic matter [37]. Water managemen<sup>t</sup> is a major challenge in the Common Agricultural Policy (CAP) and requires the monitoring of soil and crop water status to schedule irrigation e fficiently. Fertilizers and agrochemicals should be applied following the good agricultural practices, e.g., to replace only the amount of nutrients that were extracted by harvest [37].

Crop protection should be done in a way that maximizes the biological prevention of pests and diseases, in particular by promoting integrated pest managemen<sup>t</sup> (IPM) and though appropriate rates and timings of agrochemicals. Preventive crop protection can also be supported by the selection of resistant cultivars and varieties, crop sequences, crop associations (e.g., intercropping), and proper cultural practices [35].

The development of 'marginal agricultural land low-input systems', referred to as 'MALLIS', is based on the following definition: 'MALLIS is defined as a set of low-input practices which are relevant managemen<sup>t</sup> components to form viable cropping systems on marginal (arable) lands under specific climatic conditions and are sustainable in both socio-economic and environmental terms'. The implementation of MALLIS should enable farmers to cultivate industrial crops on marginal agricultural lands, considering both economic and socio-environmental aspects. Consequently, MALLIS should not only allow for profitable net farm income under the challenging biophysical growth conditions of marginal lands. It also helps to (i) reduce o ff-farm inputs, such as synthetic fertilizer, pesticides and energy (e.g., for water pumps, fuel, crop harvest machinery, storage, processing, etc.) and (ii) mitigate negative macro-economic externalities (GHG emissions, biodiversity loss, ground- and surface water contamination, soil organic matter loss, erosion, degradation, land-use change), while (iii) ensuring feasible economic benefits at farm level. Therefore, the development of MALLIS considers not only the biophysical constraints, but also socio-economic and ecological demands of the respective areas.

The conceptualization of MALLIS development always begins with the selection of the most promising industrial crop, because all other agricultural practices (tillage, fertilization, weeding, irrigation, etc.) strongly depend on the type and site-specific performance of the crop. This MAEZspecific growth-suitability ranking (and mapping) of the pre-selected industrial crops was based on the crop-suitability rankings. The basic climatical growth suitability thresholds are presented in Table 3. After the identification of suitable crops, the conceptualization of MALLIS for MAEZ was done on a general level (regional scale), since detailed best practice recommendations for the optimized managemen<sup>t</sup> of agricultural practices very much depend on local conditions (field-to-farm scale) [56–60]. Therefore, the MALLIS for the new field trials to be conducted in the MAGIC project (field-to-farm scale) were developed considering three main MAEZ criteria:

