Nutrient cycle

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The nutrient cycle (engl: nutrient cycle or ecologicalrecycling ) is in ecology, a periodic motion and exchange of organic and inorganic matter . In a rather complex multi-stage process, different organisms successively break down dead leaves or branches, for example, and transform them into inorganic compounds that are suitable for re-absorption / use by plants.

The process

Over time, leaves, twigs, fruits, animal carcasses and other organic compounds collect on the ground. The resulting layer protects the soil from solar radiation and erosion . Soil organisms, bacteria and fungi break down the organic material into simpler compounds and the gradual rotting creates the good and nutrient-rich forest soil. All of these microbial processes can also be regulated by grazing larger animals that feed on these microbes. Important material cycles that contribute to the nutrient cycle are above all the carbon cycle , nitrogen cycle and phosphorus cycle . Above all, nitrogen is important for plants, as it can be immediately absorbed by the plants as ammonium nitrogen ( ) and, as organically bound nitrogen, must first be processed by the organisms in the soil before it is processed by the plants can be included. With additional fertilizers, nitrogen and phosphates can be introduced into the soil to stimulate plant growth, but they are not always fully absorbed by the plants. The excess can find its way into rivers and lakes and affect life in these waters. ${\displaystyle {\ce {NH4-N}}}$

Short circuit and broken circuit

A short-circuited nutrient cycle describes the process in which nutrients are largely stored in the living biomass and not in the soil. Dead biomass is immediately broken down and 80 percent reabsorbed. The remaining 20 percent is lost to the ecosystem. That means that the soil is extremely poor in nutrients, there is no humus layer . Plants have developed special roots to cope with these extreme situations, such as in the rainforest.

If the nutrient cycle is broken, the dead biomass is broken down much more slowly than in a short-circuited cycle such as in the rainforest. For this reason, a humus layer can form, i.e. nutrients are stored in the soil.

Location-related examples

Nutrient cycles do not only take place on the forest floor. At different observation levels, they can also be found in water, in the rainforest and in agriculture.

Nutrient cycle in the rainforest

The soils of the rainforest are actually very poor in nutrients and are mainly iron and aluminum-containing soil that is hostile to roots. This climatic soil only retains its limited, fertile, balanced structure on its surface as long as it is permanently moist - for example in the constantly shaded jungle soil. If it dries up after the forest has been cleared or burned, only hard, strong red-brown latsole (from Latin later = brick and solum = soil) or oxisole (oxidized, i.e. used soils) or red loam soils are left. The roots of the trees in the rainforest grow and lie very flat. The forest actually only grows up and hardly out of the ground. The ecosystem that forms in the rainforest is responsible for the abundance of plant and animal species, which are nevertheless rich in species. Due to the humid and warm climate, the plants of the tropical rainforests grow all year round. As a result, leaves, branches and other parts of the plant constantly fall down. The biomass weathers very quickly due to the tropical climate . Because of the high humidity and warmth, the leaves and other organic waste such as excrement and animal corpses are remineralized extremely quickly up to a depth of about ten centimeters. Through the shallow growing roots they come into contact with the fungus mycorrhiza , which dissolve water and minerals from the soil much better than plants. They provide the plants with the important nutrients and water they need - and in return they receive substances that were created during photosynthesis by the plants. However, this nutrient cycle in the rainforest is not 100 percent efficient. The lost nutrients, around 20 percent, have to be compensated for.

Nutrient cycle in water

The plants living here, such as macrophytes and algae, are important for the nutrient cycle in the water . They serve as producers of important organic substances. Their photosynthesis releases oxygen. Here too, the most important nutrients for the growth of aquatic plants are carbon, nitrogen and phosphorus. The more nutrients there are in a body of water, the greater the plant growth. Conversely, small animals use metabolic processes to convert the organic material they eat back into inorganic substances. At the same time, nutrients are also created by breaking down dead plant and animal remains. The released nutrients are returned to the cycle. However, enough oxygen must be available for these processes, otherwise the process stops. If there are too many nutrients in the water, for example due to removed fertilizers, plant growth increases extremely. The process of eutrophication . If the majority of the biomass is present as small algae, the water becomes cloudy and the vital solar radiation is reduced.

Nutrient cycle in agriculture

In the so-called suckler cow hatching , the utilization of feed nitrogen is 6 to 9 percent. In dairy farming , it is 15 to 30 percent. This means that suckler cow husbandry can lead to significantly higher nitrogen emissions, which contribute to environmental pollution. If the nitrogen ( ) supply is higher than the consumption, nitrate leaching into ground / surface water and gaseous losses in the form of ammonia ( ) or nitrous oxide ( ) can occur. This is important because nitrate is considered hazardous to health and the eutrophication of the soil can lead to environmental problems. For this reason, the European Union introduced Directive 91/676 / EEC (Nitrates Directive) in 1991 . This should prevent too many nitrogen compounds, which are formed in the agricultural process, from getting into the soil and groundwater (see Council Directive 91/676 / EEC of December 12, 1991). According to the EU regulation, the nitrate limit value is 50 mg per liter, but this is sometimes not complied with. ${\displaystyle {\ce {N}}}$ ${\displaystyle {\ce {NH3}}}$ ${\displaystyle {\ce {N2O}}}$

Nitrogen is very important in (ecological) agriculture and is present in many compounds in the nutrient cycle. These and other nutrients can, however, lead to excessive environmental pollution. Because the soil can only absorb a certain amount of nitrogen, care must be taken when keeping livestock or cultivating land. Lellmann, Kühbauch and Schellberg explain the nutrient cycle on the basis of the nitrogen generated by agriculture on various types of land use . In order to understand the nutrient cycle, it is important to pay attention to the ecological conditions. In so-called cut grassland (meadows that are regularly mowed to obtain fodder for animals) only a small part of the nitrogen fertilization is threatened with leaching. After spreading manure, which acts as fertilizer, the soil only loses around 1 to 10 percent of its total nitrogen. In contrast, there are willows . Pastures are areas where farm animals graze. For this reason, the nutrient flow is influenced by the excrement of these grazing animals. A distinction must be made between nitrogen compounds from feces and urine. Fecal nitrogen consists of about 78 percent of water-insoluble nitrogen compounds, while urine consists of up to 90 percent of urea ( ). Urine therefore plays a major role in soil eutrophication. The leaching losses - i.e. the amount of nitrogen absorbed by the groundwater - are therefore determined by the number of these excrement sites and the duration of grazing. Not only does the type of excrement have an influence on nitrogen emissions, the weather also has an influence. In the temperate latitudes , emissions of 7 to 15 percent of urine and 1 to 5 percent of faeces can occur. In cooler seasons, emissions are lower than in hot months. ${\displaystyle {\ce {CH4N2O}}}$

Important nitrogen compounds

• Ammonia ( ) ${\displaystyle {\ce {NH3}}}$

• Ammonium ( ) ${\displaystyle {\ce {NH4+}}}$

• Nitrous oxide ( ) ${\displaystyle {\ce {N2O}}}$

• Molecular nitrogen ( ) ${\displaystyle {\ce {N2}}}$

• Nitrate ( ) ${\displaystyle {\ce {NO3-}}}$

Nitrogen enters the soil via mineral fertilizers. So that plants can absorb this, it must be mineralized to nitrate or ammonium. Plants can absorb nitrogen in this way. These plants in turn serve as food for animals. Sodium is absorbed as proteins and excreted again as ammonium, among other things. Ammonia can then evaporate into the air. Some of the nitrogen absorbed can be found in animal products such as meat or milk. Nitrification (ammonium to nitrate) releases nitrous oxide and molecular nitrogen. Some of these substances are washed out and some are released into the air. The molecular nitrogen is deposited back into the soil through deposition from the air.

hazards

Nitrate is washed out into the groundwater and ultimately into the drinking water. Ammonia acidifies the soil and thus has lasting damage to the entire ecosystem. Nitrous oxide is partly responsible for the greenhouse effect, as it contributes to the depletion of the ozone layer. Analyzes and evaluations of the environmental balance sheets of companies can help them to reduce nitrogen emissions and thus become more environmentally friendly. Phosphorus, potassium and magnesium are less of a problem for the environment, however, where possible, attention should also be paid to the amount of these substances in which they occur.

Nutrient cycle and animals

For the maintenance of biological diversity and the food chain, insects are essential, as they contribute to the structure, fertility and spatial dynamics of the soil. In agro-ecosystems in particular, insects are responsible for maintaining the nutrient cycle through their various functions, such as pollination, nutrient and energy cycles, pest control, seed distribution and the decomposition of organic matter, faeces and carrion. With the help of insects because of their usefulness in relation to the nutrient cycle, attempts are being made in the agricultural sector to reconstruct the natural cycle using habitat management practices. Despite little knowledge of the functional roles that insects play in many ecosystems, it is believed that they are more important than estimated. In addition, many animals are dependent on a large supply of food from insects. Should the nutrient cycle be disturbed, this would have an impact on the flora and insect world. In the further course, other animals are also negatively influenced. Habitat loss, pollution, harmful farming practices, climate change, exploitation of agricultural land, and the extinction of dependent species all contribute in different ways to insect population decline and insect extinction.

The relation to politics

The nutrient cycle has not only ecological and / or economic consequences, but also political ones. In Directive 91/676 / EEC, passed on December 12, 1991, the European Union agreed to protect groundwater from excessive nitrate pollution. The European Union argues that excessive nitrate levels "a nitrate concentration of over 50 mg / l [...] has a significant impact on the health of the population, particularly on pregnant women and young children." (European Commission press release). This topic became topical in the public debate when the European Commission sued the Federal Republic of Germany for failure to comply with the above-mentioned directive before the Court of Justice of the EU.

Individual evidence

1. ↑ Interview - Soil: the living treasure under our feet - European Environment Agency . ( europa.eu [accessed July 24, 2020]).
2. ↑ Nutrient cycle - fascination with the rainforest. Retrieved on July 24, 2020 (German). 
3. ↑ ^{a b} Lothar Staeck: The fascination of the Amazon . Ed .: Springerverlag. Berlin, S. 79-111 .
4. ↑ Nutrient cycle. Retrieved July 24, 2020 . 
5. ↑ EUR-Lex - l28013 - EN - EUR-Lex. Retrieved July 24, 2020 . 
6. ↑ ^{a b Council} Directive 91/676 / EEC of December 12, 1991 on the protection of water against pollution by nitrate from agricultural sources . OJ L, 31991L0676, December 31, 1991 ( europa.eu [accessed July 24, 2020]).
7. ^ Nitrates - Water pollution - Environment - European Commission. Retrieved July 24, 2020 . 
8. ↑ ^{a b c} Spiess / Richner: nitrogen in agriculture . 2005, p. 24-25 .
9. ↑ ^{a b c} Lellmann, A., Kühbauch W. and J. Schellberg: Investigations into the nutrient cycle, the performance of grassland and cattle with nutrient-extensive suckler cow husbandry and exclusive use of grassland in the low mountain range . Ed .: Agricultural Faculty of the University of Bonn. 2005.
10. ↑ Use of cut. Retrieved July 24, 2020 . 
11. ↑ Lellmann, A., Kühbauch W. and J. Schellberg: Investigations on the nutrient cycle, on the performance of grassland and cattle with nutrient-extensive suckler cow husbandry and exclusive use of grassland in the low mountain range . Ed .: Agricultural Faculty of the University of Bonn. 2005, p. 10, tables 2 and 3 .
12. ↑ ^{a b c} Pedro Cardoso, Philip S. Barton, Klaus Birkhofer, Filipe Chichorro, Charl Deacon: Scientists' warning to humanity on insect extinctions . In: Biological Conservation . tape 242 , February 1, 2020, ISSN  0006-3207 , p. 108426 , doi : 10.1016 / j.biocon.2020.108426 ( sciencedirect.com [accessed July 24, 2020]).
13. ↑ ^{a b} Press corner. Retrieved July 24, 2020 .