Field of Action Agriculture
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Temperature largely determines the suitability of a crop species for cultivation and significantly influences growth and development processes. All cultivated plants have a temperature range within which they grow optimally. It differs from species to species and also depends on the particular stage of development of a plant. For example, the optimum for plant growth of wheat is between 10 and 25°C. If the temperature deviates upwards from the optimum temperature range, the plant suffers from heat stress, which manifests itself through certain symptoms on the plants (e. g. wilting symptoms, poor flower initiation, lack of fertilization, fruit deformation, poor coloration of fruits). In combination with high solar radiation, temperatures can be reached at the plant surface that lead to burns on leaves (e.g. of wheat, vegetables) and fruits. Damage occurs to proteins and thus to metabolic processes. At very high temperatures, this usually leads to growth stagnation and to losses in quality and yield. The heat year 2003 shows for various regions in Germany (e. g. Rheingraben) that a significant drop in crop yields correlates with the number of heat days.
The individual crops tolerate heat differently: rapeseed, sugar beet and potatoes are relatively sensitive to heat. Cereals, especially barley, are somewhat more tolerant, but also show yield depression with increasing heat. Crops of subtropical origin, such as corn, millet, and soybeans, on the other hand, are fairly heat tolerant. In grasslands, there are also grass species that are particularly sensitive to heat, e. g common bluegrass (Poa trivialis), while other grass species are more heat tolerant, e.g., Kentucky bluegrass (Poa pratensis) and tall fescue (Festuca arundinacea). Most crops are particularly sensitive to heat stress at certain sensitive stages of development. In wheat, flower unfolding and pollen differentiation in May/June are such phases when temperature rises above 30 °C can lead to sterile pollen and thus a decline in grain number. In rapeseed, very high temperatures during the growth phase decrease the content of nutritionally desirable unsaturated fatty acids, while increasing the content of saturated fatty acids. Cereals react to heat stress in the ripening phase with so-called emergency ripening. The grains remain smaller and the yield is lower. The decisive factor here is therefore when the heat phases occur in the near and distant future and whether they occur more frequently during the sensitive development phases of the crop plants. Crop heat sensitivity or tolerance is not an isolated phenomenon, but must always be seen in the context of water supply, whether through precipitation or soil water supplies. Heat has a worse effect the less evaporative cooling (transpiration) can provide relief, i.e., the drier it is.
In terms of the potential extent of damage, areas with a high proportion of fruit cultivation, viticulture and horticulture are particularly vulnerable, since yield and quality reductions in these special crops with high added value have a particularly strong impact. In contrast, regions with a high proportion of grassland are more adaptable, as grasslands can change their species composition.
Cold stress means stressing plants at low temperatures. At lower temperatures, chemical processes run more slowly, which for plants generally means less energy from operating metabolism, lower nutrient and water uptake from the soil, and slower growth. As a result of cold stress, leaves may turn yellow and wilt. Below 0°C, frost damage occurs on many crops due to ice formation in the cells, which destroys cell structures. For some crops, such as winter wheat, a climate change-induced decrease in frost days is problematic because a cold stimulus is required during a certain growth phase, the plant's transition from the vegetative to the generative phase ("shooting"). If this is lacking, crops suffer. Late spring frosts are among the most dreaded extreme weather events, especially in fruit cultivation, viticulture and horticulture. They cause damage to leaves, shoot tips and flowering plants and inhibit fruit development. Frost cracks and frost scars on the fruit lead to qualitative impairments, some of which can no longer be marketed as a result. As a rule, the risk of late frost damage is higher in early-sprouting varieties, very early-sown or planted stands, and at lower altitudes. In the case of apple and wine crops, the more advanced plant development is in spring, the more devastating the damage can be. Special attention should be paid to the increasingly earlier start of vegetation due to climate change, which increases the probability that plants are already in very late frost-sensitive development stages.
If the soil water content falls below a critical value, a supply of water and nutrients to the plant roots and their transfer to other parts of the plant is no longer sufficiently guaranteed. The plant goes into drought stress. During drought stress, many plants close their leaf openings (stomata) to evaporate less water. However, this also results in less evaporative cooling and the tissue temperature of the plants increases. For agriculture and fruit cultivation, wine- and horticulture, the temporal distribution of precipitation plays an important role in addition to the annual precipitation total. Long periods without precipitation lead to changes and damage in all stages of plant growth. The effects are particularly severe when water stress occurs during sensitive plant growth stages, such as leaf formation. The lack of soil water impedes the availability and uptake of nutrients and leads to a reduction in photosynthesis. This can cause growth and maturity inhibition, yellowing, early autumn coloration, and leaf fall.
Agricultural crops have different levels of tolerance to drought stress. While shallow-rooted plants such as potatoes are very sensitive to low soil moisture, apple, grapevine and asparagus have very deep-reaching roots and can thus access a larger volume of soil water. They are comparatively less susceptible to drying out of the upper soil horizons. However, even these deep-rooted crops suffer from inadequate coverage of their water requirements as a result of prolonged drought, leading to damage. According to data from the German Meteorological Service, the number of days with low soil moisture has already increased significantly in Germany since 1961 and, depending on the region, has led to significant crop losses with corresponding economic damage. Particularly in southwestern Germany and parts of the eastern states, decreasing precipitation in the summer half-year and more consecutive dry days can be observed as a result of climate change. In these regions, which are already comparatively warm or dry, climate change is becoming increasingly problematic for agriculture.
Excessive precipitation can also affect plant growth and have negative consequences for agriculture and horticulture, fruit cultivation and viticulture. In this context, extended periods of wetness (continuous rain) with waterlogged soil represent an extreme weather situation in two respects. First, plant roots suffer from a lack of oxygen, which damages the root system. As a result, there is stunted growth, delayed ripening, yellowing, and increased vulnerability to pests. In the worst case, the plants and trees die. Secondly, the soil is so wet that it is impossible to drive agricultural machinery over it to sow, tend and harvest the crops without causing damage. As climate change progresses, it must be assumed that heavy precipitation in Germany will increase with a high to very high probability in the coming decades. In addition to yield losses due to excessive wetness, heavy rainfall is often accompanied by increased surface runoff (water erosion) and thus causes damage to agricultural land and infrastructure.
In extreme cases, hail can destroy the entire harvest of a cultivated area in arable farming and in the special crops of horticulture, fruit growing and viticulture, thus causing high economic damage. In particular, hail causes mechanical damage to above-ground plant parts, leaves and crop. By perforating or even knocking off the leaves, the assimilation area and thus the photosynthetic output are reduced. Damage to the crop can cause secondary infections and a delay in ripening, in addition to visually affecting quality. According to insurance companies, hail is already occurring more frequently than in previous decades. In general, an increase in the risk of hailstorms from northern to southern Germany is assumed in the course of climate change.
Storms can also cause mechanical damage to agricultural crops and specialty crops, either directly by the wind or by wind-transported particles (wind erosion). Strong wind gusts are capable of toppling entire trees, causing damage to support equipment in viticulture, or breaking entire shoots in vegetable crops. Often, significant delays in development and maturity occur as a result of this damage. Pressure spots, scuff marks (e.g. from support devices) or abrasions can occur on shoots or crops. This results in qualitative losses and creates entry points for pathogens. In general, the risk of major storm damage to permanent crops increases as development and leaf surface progress. For example, vulnerability to storms is particularly high when apple and wine have high fruit hanging. Excessively high wind speeds also hinder the application of crop protection products. Wind erosion can lead to drifting and thus to a transfer of pesticide active substances to other areas.
Indicators from the DAS monitoring: Yield fluctuations | Hailstorm damage in agriculture
In times of climate change, increasing heat stress, water shortages and feed shortages are probably the biggest challenges for livestock farms. Heat stress reduces the well-being of livestock and can affect their health and performance.
Dairy cows, which are very sensitive to temperature increases, respond to heat stress by reduced feed intake, increased water intake and standing. Consequences may include a reduction in milk quantity and milk quality (fat and protein content), impairment of the immune system, metabolic disorders, lower fertility, and increased embryonic lethality. If heat stress occurs in the last three months of gestation, calves may have lower birth weight and metabolic problems after calving. In addition, the milk yield of these animals may be limited when they are old enough to produce milk. High-performance breeds among dairy cows, in particular, are considered increasingly sensitive to heat. They have difficulties compensating for heat exposure because milk production is accompanied by high heat production of their own. Other factors influencing heat stress in individual animals include coat color and health status. Animals of the same breed from cooler regions suffer from heat stress more quickly than animals from warmer regions.
Pigs are also particularly sensitive to heat stress because they do not have functioning sweat glands and can only remove heat by panting. Therefore, heat can quickly become critical for the animals. Critical temperatures are reached in pig farming with outside temperatures as low as 25°C. To prevent a rise in body temperature due to digestive heat, pigs cool themselves by increasing respiration, which leads to water loss and reduced feed intake. Another strategy of the animals is to avoid physical contact with conspecifics when space permits. As a result of heat stress, there is decreased welfare to circulatory failure and increased mortality. During hot periods, the fertility performance of boars and the farrowing rate of sows also decline, and litter sizes decrease. Sows react to high temperatures with decreasing milk yield and become more susceptible to disease. These and other parameters have a direct impact on economic efficiency.
Poultry is also very sensitive to heat. For example, heat stress in young fattening poultry begins at around 30°C. Laying hens tend to prefer 18 to 24°C. When it gets too hot for chickens, they spread their wings sideways from their bodies. This allows cooler air to get under the feathers to the skin and warm air to escape. Chickens also release heat through their tongues and mucous membranes. When breathing with an open beak, moisture is released and the resulting evaporative cooling is used for cooling. Hens react to the onset of overheating with a decline in laying performance, accompanied by smaller eggs, thinner shells and lower egg quality.
In addition to heat stress, climate change can also affect the performance of livestock through more indirect pathways. For example, climate impacts on crop production can reduce forage quality and availability.
Lengthening of the growing season: The continuously rising average air temperature extends the growing season. In particular, fewer frost days in spring can lead to an earlier start to growth. The overall higher temperature totals can thus increase yields in arable farming, fruit cultivation, viticulture and horticulture. However, an earlier start to vegetation increases the risk of late frosts and thus the risk of yield losses. This affects fruit cultivation in particular. Decoupling of flowering and pollinators is also possible for some crops. Changing plant phenology also has implications for agricultural operations and crop management. Corn and sugarbeets in Germany are already sown and harvested ten days earlier on average than in the period from 1961 to 2000.
Shift of cultivation areas: On average, higher temperatures and milder winters lead to a shift of cultivation areas towards the north and higher regions. Crops that require a certain cold stimulus in winter can no longer be cultivated regionally due to higher temperatures. However, new warmth-loving crops can be added, whose cultivation was previously not possible or not economical in Germany. In particular, cultivation areas in Germany that are comparatively cool and humid today (e.g. northern Germany, low mountain ranges) can benefit from these developments and, given a moderate rise in temperature and an adequate water supply, may certainly expect increased yield potential for many types of crops.
Stress from pests and diseases: As a result of rising temperatures, we can expect a spread of plant diseases as well as pests that were previously found only in warmer areas. Other pests, on the other hand, which depend on longer periods of moisture, could decline. As a result of climate change, shifts in the species spectrum of plant pests can therefore be expected in the coming years. Damage caused by fungal diseases - with the exception of diseases triggered by warmth-loving fungal species such as mildew - is likely to decrease in many areas.
Indicators from the DAS monitoring: Agrophenological phase shifts | Infestation with harmful organisms - case study
In the field of action agriculture (crop production), adaptation activities can start with the type of soil cultivation and treatment, irrigation, the choice of plant varieties and frost protection. In addition, technical measures are relevant that improve weather forecasts and warning systems and enable farmers to adapt to weather changes and extreme events in time and to initiate protective measures.
With regard to the increasing heat stress in the summer months, early cereal varieties can be used, although negative effects on grain yields are to be expected due to the lower radiation at the earlier stage of the growing season. Climate changes also allow the introduction of crop varieties that have hardly been cultivated in Germany so far. Particularly suitable are certain varieties of corn, millet and other warmth-loving species that use water effectively. For example, the cultivation of soybeans has expanded significantly in Germany in recent years.
In arable farming, fruit cultivation and viticulture, various measures are used to counter the risk of late frost. In general, cultivation in frosty areas (e.g. valleys, sinks) should be avoided and the variety selection (winter hardiness) should be adapted to the respective location. In arable farming, more winter-hardy varieties or even crops (e.g. rye) can be cultivated to avoid cold frost damage. In fruit cultivation, frost protection irrigation has proven to be an effective measure. In the Lower Elbe region near Hamburg, for example, about 75% of the fruit-cultivation area is equipped with frost protection irrigation. Here, fruit trees are iced by continuous sprinkling during frost. The heat energy released when the water freezes prevents the blossoms from freezing. Considerations for sprinkler irrigation are the high water and energy consumption, the provision of an adequate water supply, and the risk of soil watering. In viticulture, wind turbines and wind machines can be used to mix cold and warm air layers to reduce the risk of late frost. In addition, frost candles can be used in the rows of vines, which can also reduce the risk of late frost through the heat generated when wind conditions are favorable.
In order to counteract the negative effects of drought stress, water-saving and site-adapted soil cultivation, irrigation measures and variety selection are primarily used in agriculture. The avoidance of plowing or conservation tillage, the cultivation of alternating plant species (crop rotation) and catch crops, the promotion of humus buildup, and year-round soil cover through undersowing or through a mulch layer can reduce the evaporation of water from the soil. In addition, these measures have other positive effects: an increase in soil fertility, a reduction in the risk of erosion by wind and water, and nitrate contamination of groundwater by binding nitrogen. Irrigation can be an effective adaptation measure in the event of increasing dry periods, in order to ensure the field emergence of crops as well as the yield level and quality of harvested products in the future. In some regions of Germany, economical cultivation of potatoes, fruit, vegetables and some specialty crops will largely be impossible in the future without irrigation. Irrigation should use water-saving irrigation methods with high water use efficiency that is controlled according to soil moisture, e.g. drip irrigation. The required additional water can be made available by removal from groundwater or surface water, water storage reservoirs, or water transfers. In Germany, the removal of irrigation water from groundwater and surface water is legally regulated by the Water Resources Act and corresponding regulations of the federal states. Given the sensitivity of plants to the combination of heat and drought, it can be assumed that the importance of irrigation in agriculture will increase in the course of climate change in Germany. Both the EU and the federal government support irrigation infrastructure in agriculture, e.g., at the European level the European Agricultural Fund for Rural Development (EAFRD) and in Germany through the Joint Task "Improvement of Agricultural Structure and Coastal Protection" (GAK). Irrigation measures should, if possible, only be promoted in areas with a sufficient supply of supplementary water, where they should focus on water-saving or efficiency-enhancing irrigation measures for reasons of resource-conserving water use.
Seed selection should also be adapted to climate change. In particular, varieties that are less vulnerable to drought and heat stress and prove robust to pests are suitable for effectively countering climate change. In general, diverse cultivation and the use of robust varieties and crop species can reduce the risk of crop failure.
As a precautionary measure against the stress factors of wetness, continuous and heavy precipitation, sites with waterlogged soil layers should be avoided in arable farming, fruit cultivation, viticulture and horticulture. This also applies to the selection of varieties sensitive to waterlogging. The measures predominantly used for areas prone to waterlogging are drainage methods, which can be underground or above ground, as drainage or ditch drainage, and free or regulated. As a cultural-technical measure, a soil cover or a greening in steep slopes can contribute to the reduction of erosion risk. Appropriate soil cultivation and wide tires for agricultural machinery help to avoid soil compaction. In orchards, vineyards and horticulture, the conclusion or promotion of an insurance policy against heavy rainfall can be considered as a management measure.
In regions where hail events occur quite frequently (e.g. southern Germany), hail protection nets are used in fruit and wine growing as a common adaptation measure. The measure is cost-intensive, but has a high degree of effectiveness and an additional benefit through bird repellency. If used on a large scale, negative ecological effects are to be expected, e.g. on biodiversity. Alternatively, farms can take out hail insurance to cover damage caused by hail.
Strong winds and storms, which can cause wind erosion, are a challenge for soil protection and thus also for agriculture (see Field of Action Soil). In addition to site-adapted tillage and the establishment of windbreak hedges, agroforestry systems (agroforestry), the joint cultivation of arable crops, grassland or special crops with trees can be an effective adaptation measure to reduce wind erosion. Such systems also increase soil fertility and water-holding capacity in the soil, create a favorable microclimate on site, and increase biodiversity.
Indicators from the DAS monitoring: Cultivation and propagation of thermophilic arable crops | Adaption the variety spectrum, maize varieties by maturity groups | Use of pesticides | Agricultural irrigation
Adaptation measures in the livestock sector are extremely important in response to the effects of climate change on livestock, particularly the consequences of heat stress on animal health and performance features such as milk production. Structural and technical measures can be considered to reduce heat input and promote heat removal in freely ventilated outdoor barns, such as consideration of the siting and orientation of new barn construction, adequately thermally insulated roofs, sufficient roof overhangs, green roofs, light-colored roof surfaces to take advantage of the albedo effect, natural shading from trees on the south side of the barns, and flexible wall designs to allow airflow to be regulated. Fully air-conditioned barns, which are characterized by a high degree of automation with regard to the control of ventilation, temperature and humidity, can be used to specifically counteract a hot spell. Aspects relevant to climate mitigation should be taken into account (e.g. low energy consumption). In barns without such automated cooling facilities, as well as in open barns, fans can be used for active cooling to increase air velocity and air exchange rate, as well as evaporative cooling measures such as cow showers and water sprinklers. In addition, an optimal drinking supply must be ensured in the barn, in the waiting yard and at other suitable locations on the farm.
Climate change also increases the risk of heat stress in grazing animals. Possible responses to this include changes in pasture management, such as the use of night grazing. In certain regions, there is the option of shifting grazing to higher cooler areas. Another suitable measure against heat stress may be to plant shade trees in the pastures.
Finally, adaptation options also exist in terms of breeding, by favoring robust breeds and breeding lines of dairy cows that are better adapted to warmer climatic conditions. This is where breeding programs for climate-adapted livestock breeds can come in. The issue should also be increasingly incorporated into education, training and agricultural consulting. As climate change progresses it may also be necessary for animal production to adapt the regulatory and subsidy framework to the changed conditions. This concerns, for example, the regulations for animal houses (insulation, ventilation) or the adaptation of regulations for organic farming (adaptation of grazing periods during periods of extreme heat).
Changing sowing dates, for example, can address the shift in seasons: Summer cereals could be sown earlier to take advantage of spring soil moisture. Winter cereals, on the other hand, should be sown later in the year so that the cold phase, which is important for cereals, does not occur too late. In the transitional phases, the use of deep-rooted crops, such as grasses, can reduce the risk of drought damage in summer and protect the soil against erosion.
Indicators from the DAS monitoring: Adaptation of management rhythms