CLIAVEClimate Focused Agricultural Vocational Education

Module 1 · Chapter 6

Alternative crops growing for biomass production

Jaroslav Bernas, Petr Konvalina, Jaroslav Neumann · 19 min

ENTRCSROSRSL

Importance of Alternative Energy and Forage Crops

Biomass from alternative energy and forage crops is a universal source of energy through which it is possible to produce both heat and electricity, as well as fuels in a gaseous, solid, and liquid state [23] or produce valuable forage biomass for animals at the farm [31]. Biomass, among which the alternative crops for energy belong, is considered a renewable energy source (RES) and has long had huge potential for mitigating the effects of global warming [34].

Of particular importance is the multifunctionality of biomass, which includes food production, energy and feed sources, biodiversity conservation, and social services in society. It also brings new opportunities for managing and researching strategies in forestry, agriculture, agroforestry, and pasture to mitigate global warming [11] or [28] and positively contribute to relation to the climate resilient cropping system.

The importance of alternative crops for biomass production can be summarized in accordance with three main pillars: social, environmental, and economic. In the case of social benefits, energy crops could benefit the production of indigenous renewable energy, which in turn increases energy security and improves trade balances. This will lead to the creation of alternative sources of employment in rural areas. Production of energy crops could lead to the creation of farmers' associations/cooperatives. Energy crops growing could improve the education, training, and assistance services provided for farmers. From the perspective of the economic benefits, the production of energy crops can lead to the development of new and profitable markets (biofuels, chemicals, materials, foods, feeds, etc.) that could provide farmers with new sources of income and employment. Incorporation of energy crops can promote the development of regional economic structures and can create higher-value coproducts. From the perspective of climate resilient cropping systems, the environmental benefits are crucial because the production of dedicated lignocellulosic biomass crops (energy crops in this case) has the potential to provide a range of benefits for water quality improvements, phytoremediation, and treatment of wastewater and sludges, carbon emission reductions (GHG), and biodiversity. Even the soil degradation problems could also be reduced when perennial herbaceous and short-rotation trees are grown. Thanks to the implementation of energy crops into the growing system, the pressure on finite natural resources can be reduced. Energy crops can significantly promote the use of marginal lands and can support wildlife, natural habitats, and overall agrobiodiversity [41].

Alternative Energy and Forage Crops Potential in Relation to the Threat of Drought

One of the main threats to agriculture is drought. Drought can significantly affect the composition and functioning of all cropping systems and needs to be responded to appropriately. Alternative energy or forage crops can bring certain solutions. Drought is often considered a major threat to ecosystems in global climate change. Water stress limits biomass yields more than all other biotic and abiotic factors combined. The frequency and extent of the regional dry season are constantly increasing. Recently predicted scenarios of more frequent dry spells and heat waves for Europe and the Mediterranean region have come true [40], and so have most climate change scenarios that predicted increasingly extreme precipitation fluctuations, i.e., longer dry spells alternating with large precipitation totals [13], or scenarios predicting increased water consumption for agriculture. One of the most common reactions of crop roots to drought is an increase in root length. This reaction is typical for annual plants, especially for agricultural crops [5]. A plant's chances of surviving extreme drought stress are greater the longer it can delay a dangerous reduction in the water potential of the protoplasm (ability to delay desiccation) and the more the protoplasm can dry out without damage (ability to tolerate desiccation). It is also important that tolerance to different soil moisture (drought) also depends on the stage of plant development [13]. A lower demand for water should rather be understood as the ability of the given species to survive even in conditions with a limited supply of moisture, regardless of the amount of production. In drought-resistant plants, we find that they have open stomata even when there is a lack of water. Some plants roll up and fold their leaves (as some of the energy grasses) [22]. A number of alternative energy crops are included in cropping systems precisely because of drought resistance or the low water requirement [24] or [18]. A distinction must be made between soil drought, characterized by a lack of physiologically available water in the soil, and atmospheric drought. Atmospheric is particularly dangerous because it sets in in a short period of time, and crops usually cannot adapt to it. The resistance of plants to lack of water is not the same throughout the growing season. It decreases the most in the so-called critical periods.

Drought resistance

Plants (mainly agricultural crops) can also be bred for drought resistance. Drought resistance is a property that allows plants to endure a period of drought (water deficit in the soil) or a period of high temperatures and associated air dryness without significant deterioration of development and reduction of production. Species that are inherently drought-resistant or generally have low water availability requirements can also be selected for plant production systems. This refers precisely to the selection of alternative energy crops suitable for energy or forage purposes [24] or [18]. Drought resistance and high temperature resistance and their combinations are advantageous for arid regions, but they do not have such applications in regions with highly variable weather, only as part of broad adaptability [5]. Drought resistance is a complex property, as it depends on a number of circumstances and factors: the amount and strength of the root system, the ratio of above-ground and underground mass, the morphological and anatomical peculiarities of stems and leaves that can affect the water management of crops, the regenerative capacity and speed of development, etc. The genetics of drought resistance are very complex due to the many factors that condition or influence it [15]. Drought resistance is a complex trait, and it is, therefore, difficult to test it, unlike a number of other traits, only in field conditions, where a number of different stressors act and the reproducibility of results in individual years is difficult. Tolerance and resistance to drought in general, species, and varieties of individual crops are based on different physiological laws [5]. Testing drought resistance is methodically quite difficult. Rather, laboratory methods are chosen by comparing the formation of mass (dry matter) in drought conditions and in irrigation conditions, in climate chambers, or indirect methods are also used. In field conditions, the production achieved by new breeding or varieties in dry areas (vintages) and in areas with a normal course of the year is compared.

Alternative energy crops

There are already selected potential crops for bioenergy production for European environmental areas suitable for energy purposes, meeting the requirements of the bioenergy industry efficiently. Not all crops possess the necessary attributes, and therefore, suitable plants and practices must be identified for each agroecological zone, with continuous improvement to reduce pre-treatment, cultivation, and conversion costs. Among the potential crops for bioenergy production within different European environmental zones belongs: Maize, Mustard seed, Hemp, Linseed, Castor bean, Clover or alfalfa, Sugarbeet, Oil seed rape, Sunflower, Potato, Wheat, Other cereals, Sorghum, Cardoon, Giant reed, Reed canary grass, Miscanthus, Switchgrass, Eucalyptus and Poplar and willow. These crops vary in terms of yield, agri-environmental ranking, and geographical suitability [28].

Annual Versus Perennial Energy Crops

The choice of the most suitable alternative energy crops is crucial, especially in terms of strategic and effective replacement of the traditional ones and reduction of greenhouse gas emissions [39]. Selected alternative crops should have a high yield and energy potential, along with only minimal environmental impacts [6]. The decision based on the annual or perennial crop implementation can also be opened. Total energy efficiency (i.e., the ratio of energy input to energy gain) is higher for perennial crops than for annual (depending on yields and intensity of cultivation) [21]; [3]. The positive environmental effects mainly from the plantations of perennial crops due to the soil coverage and higher CO2 sequestration [9]; [10] and biodiversity promotion [8]. In general, they have a better impact on the environment than traditional annual crops and are associated with higher biomass yields, better yield stability of clean energy, and lower environmental impacts [12]. The area that will then be defined for growing alternative energy and forage crops should be based primarily on yield potentials, production intensity, and the type of technology used [6]; [3]. Also, the production of annual crops can become more environmentally friendly, for example, when tillage in crop rotation is carried out in a minimized mode, and the soil can function as a carbon sink [36]. However, the advantage of annual energy crops is the well-known and routine production technology, the flexibility to change the type of crop and acreage, and the possibility of applying part of the production at market food, feed, or energy prices.

Alternative Crops Growing for Energy and Forage in Relation to Climate Change Mitigation

Agricultural activity contributes significantly to environmental damage, mainly due to land use, fertilizer use, and energy consumption. The main potential for improvement often includes increased biomass yield and potential energy gain, the choice of gentle agricultural practices, and the exclusive cultivation of perennial crops [20]. On the other hand, one of the disadvantages of the crops intended for eco-energy is that they compete on arable land with food crops [33]. This is not the same in the case of forage crops because they serve as a primary source of biomass for animal feeding. Therefore, the cultivation of energy crops is recommended, especially in marginal areas [27] or on low-production or otherwise degraded soils [38]. In general, there are main criteria for rating the sustainability of energy: use and changing the use of lands, the water footprint of energy crops, the impact of energy crops on biodiversity [8], climatic change, C sequestration, mitigation of GHG (balance and life cycle), and maintenance of soil fertility [28].

To apply the principles of sustainability, it is necessary to identify cost-effective ways to avoid, at least in part, GHG in the agricultural sector as well. If we are to think about mitigating greenhouse gas production within the selected cultivation processes, it is necessary to focus primarily on their strongest sources. These are the production and use of nitrogenous fertilizers and field emissions related to their production and application. Reducing the dose of fertilizers or the overall change in the agricultural system can be the solution [36]; [14]. After all, reducing the dose of fertilizers used in the agricultural sector has long been considered a key activity in reducing N2O and NO emissions. The amount of GHG from agriculture is largely also affected by the management system. Conventional agricultural systems are based on higher inputs of fertilizers (organic and mineral), which are key factors for the mitigation of N2O and NO emissions from soil. N2O can be considered the main greenhouse gas, and ecological management systems usually produce less (also CO2) due to generally lower inputs [7]. The majority of emission flow can be considered the one that is connected to the production and use of mineral fertilizers and the consequences of their application. In the agricultural sector and especially in the crop production sector, nitrogen fertilizers represent a relatively complex problem. For example, Boehmel et al. [6] state that N fertilizer tends to have a 41-64% share of energy consumption in annual crops and a 17-45% share in permanent crops. At higher doses of N, there is no longer a significant increase in biomass [25]. The efficiency of the fertilizer used decreases with increasing fertilization doses because the plant does not take up a large part of the fertilizer and instead enters the water or air [32] in the form of so-called field emissions. One of the general advantages of perennial grasses is fewer nutrient requirements and inputs in the form of chemical protection products than annual crops [29].

Another way to reduce GHG is to replace traditional crops with another crop that is also suitable for the chosen purpose, i.e., forage or energy purposes. Respectively, the possibilities of GHG mitigation can be achieved through the cultivation of less intensive perennial crops [2]; [26]. These can be, for example, perennial grasses, which are also suitable due to their properties [3], highly productive species of annual and perennial crops or their mixtures that have already been selected and particularly implemented [37]. However, for example, maize cannot yet be fully replaced by them from the perspective of biomass production [16]; [3]. But from the point of view of GHG mitigation in the cultivation of maize, crop rotation and intercrops incorporation, no-till tillage systems [36]; [1], or effective N fertilization management can bring the solution [30]. Nevertheless, due to the nature of perennial crops and generally lower fertilization requirements, alternative crops for biomass production are expected to have lower environmental impacts during their life cycle than traditional annual crops grown so far [17].

Yield Improvement Potential

The possibility of improving the yield potential is in the selection of appropriate crop species and genotypes for the given locations to suit the specific soil types and climate. If alternative energy or forage crops are to be produced sustainably, cultivation practices for energy crops should be optimized rather than maximized, as generally low-input systems requiring reduced inputs of nutrients and agrochemicals are needed. The traditional plant breeding, selection, and hybridization techniques are mostly slow. For example, much of the miscanthus currently grown in Europe is derived from sterile triploids that are propagated through expensive cuttings that can be susceptible to late frosts. Therefore, future research can be targeted to increase productivity by reducing sensitivity to cold temperatures.

Given the limited breeding experience to date, it is likely that major advances in bioenergy crop yields, for example, through genetically and non-genetically modified crops, can be expected in the next few decades. Both quantity (the amount of biomass yield) and quality (for example, plant structure or the chemical nature of the input raw material) are identified as the goals of future breeding, while the main task will be to support the resistance of plants to climate fluctuations, the support of a climate resilient cropping system, respectively. Although genetically modified energy crop species may be more acceptable to the public than genetically modified food or feed crops, there are still concerns about the potential environmental impacts of such plants, including gene flow from non-native plants to native plant relatives. As a result, non-genetically modified biotechnologies (i.e., selection of drought-tolerant or frost-resistant plant species) may remain particularly attractive [35].

Perspective

In general, agronomic research, development, and management of alternative energy crops lag far behind established annual food crops. The reason is mainly that in the past, the role of agriculture in energy production was not considered a strategic issue. This situation has recently changed due to increased environmental concerns and the increased cost of fossil fuels. The production of energy crops is expected to benefit the development of new markets, support regional economic structures, provide alternative sources of employment in rural areas, promote the use of marginal lands, bring a reduction of CO2 levels, and reduce dependence on centralized resources. Therefore, in the long term, successful implementation of energy crop systems should strive to ensure income generation, environmental sustainability, energy security, flexibility, and replicability [41].

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