Mulberry trees can grow in the tropics
Wear silk, plant mulberry trees
For 8000 years almost everywhere in the world the fertility of the soil was considered a gift from the gods. In China, however, it was the duty of the peasants, princes and officials to protect and promote soil fertility. This was the only way to ensure food safety in the most densely populated country for many generations. The cultivation of mulberry trees and the breeding of silkworms played a central role. In addition to elegant silk, protein-rich food, animal feed and, last but not least, humus-building compost were created. Even today, mulberry trees, caterpillar compost and natural silk could make destroyed soils fertile again and turn farmers worldwide into prosperous climate farmers.
When China's population grew rapidly 5,000 years ago, more and more fertile soils were needed in the country to provide food, animal feed, clothing, building materials, and firewood. By observing how natural systems develop and how fertile soils are created from barren land, the value of trees as regulators of the microclimate and as pumps for nutrients and water was recognized even back then. At the behest of emperors and natural philosophers, the massive cultivation of mulberry trees (Morus alba) began, which also thrive on the poorest soils. The wood has the calorific value of oak, and beautiful furniture as well as paper can be made from it. The leaves are used to brew tea, are used in medicine and are a nutritious feed for cattle, goats and sheep. They are particularly eaten by the caterpillars of the silk moth (Bombyx mori), from whose cocoon the threads for the coveted natural silk are obtained.
Legend has it that the secret of silk was discovered by the Chinese Empress Si-ling-chi when a silkworm cocoon fell into her tea while she was sitting under a mulberry tree. She noticed that the treatment in hot water released a strong thread from the cocoon. This then gave rise to the idea of weaving the threads. In fact, it was possible to produce soft, shiny silk fabrics with amazing properties.
The knowledge of sericulture, the reproduction of the mulberry trees and the production of silk was closely guarded in China for more than 3000 years. The death penalty was incurred for betraying the secret. Silk had become an important economic factor, a lucrative export commodity, because Chinese silk was a sought-after luxury good in ancient Egypt and later in the Roman Empire.
A fantastic material from nature
The silk of the silkworm is the only naturally occurring continuous textile fiber. It consists mainly of proteins. Their production and processing requires a lot of experience and care. Silk can be stretched around 15 percent without tearing; it cools when it is hot and warms when it is cold; it can absorb up to 30 percent of its own weight in moisture without feeling wet; the surface is dirt-repellent and neutralizes bad smells; Silk is wrinkle resistant and dries quickly; a thread made of silk can hold more than a wire made of steel of the same thickness. It's downright fantastic: The energy of the sun is the basis for the growth of the mulberry tree leaves, which are eaten by the silkworms and converted into cocoons made of silk threads. These silk threads are highly complex, natural polymers that, unlike synthetic silk, do not consume any finite raw materials such as crude oil or natural gas.
Well kept secret
Knowledge about the production of natural silk spread very slowly, first to Korea, India and Japan. It was not until 550 AD that Christian monks succeeded in stealing part of the secret and bringing it to Constantinople. From there the knowledge about Italy reached all of Europe. Today it is hardly known that Frederick the Great planted millions of mulberry trees in the 18th century. In 1785 Prussia produced seven tons of silk which provided employment for 30,000 looms and 12,000 people. Before the outbreak of World War I, France produced 500 tons, Italy 4,100 tons; Even in Switzerland, 2.5 tons of raw silk were produced annually. In the 1920s and 1930s there were numerous initiatives in Germany to promote silk production. The aim was to become independent of raw material imports, because, not least as part of the preparations for war, large quantities of parachute silk were required, among other things. When, after the war, it became possible to produce cheap artificial silk from crude oil, the Europeans found the production of natural silk to be too costly, and practical knowledge of sericulture and raw silk production was lost.
Silk - originally just a by-product
While the connection between silk and the mulberry tree is well described in Western cultures, the main reason why mulberry trees were planted in China went largely unnoticed. The sheen of the silk dazzled then and now the view of the true value of the sustainable cultivation system that goes hand in hand with the traditional cultivation of Morus alba. Mulberry trees also thrive on dry and barren soils, but act there as pioneering plants for making the soil fertile. They root and loosen the soil, ensure increasing biological activity and constant input of carbon through the high leaf yields. Depending on the site conditions, variety and cultivation method, a plantation sheds 5 to 30 tons of leaves per hectare and year - that is more biomass than grows on a maize field of the same area planted for biogas production!
One kilogram of caterpillars (2 million larvae) eat up to 24 tons of mulberry leaves in the course of their life. After four moults, the caterpillar has finally fed 10,000 times its original weight. Now it's about the thickness of a finger and the transformation can begin. In four to eight weeks she will spin a fluffy silk cocoon. Silk threads up to 1000 meters long can be pulled from such a cocoon. At the end of the cycle, the white silkworms will eventually transform into brown pupae.
To separate the brown dolls from their cocoons, they are killed by brief heat, which is a terrifying sight even for non-vegans. Both the caterpillars and the pupae are valued in China as a valuable addition to the protein diet of humans and animals. They can still be found today in Asian markets, where they are often bought, prepared and eaten.
To obtain one kilogram of raw silk, up to ten kilograms of cocoons are required, for the production of which, in turn, the leaves of around eight mulberry trees are required. On a plantation of one hectare, around two tons of silk can be produced annually, with up to 18 tons of silkworm excrement. It is this dung that has long been regarded as the actual main product, because through targeted treatment, the humus soil that ensured the safe, high food yields of traditional Chinese agriculture was created from it. The silk was basically just a valuable by-product.
The leaves of the mulberry trees, which are used for silk production or as fodder, are not picked individually from the trees. Instead, leaf-bearing branches are cut from the tree with a sickle and only then defoliated in the rooms set up for silk production. Goats and cows do not have to defoliate and hang their branches in the barn. Finally, the plucked or eaten off branches are ideal for making biochar from them in traditional burial piles (see Oya issue 38). If the biochar is soaked in the urine of the farmers and their draft animals and then mixed with the silkworm excrement, one of the most valuable organic fertilizers is created. In this way, as the population grew, the Chinese were able to increase soil fertility and thus produce more and more food. They could make barren land fertile in the foreseeable future.
Over the silk road to Europe and back
When the production of silk slowly gained a foothold in Europe from 550 AD, the people of this continent were obviously not culturally developed enough to recognize the value of humus and the farmers' responsibility for its maintenance and development. The Chinese, however, had already started a soil improvement program three millennia earlier, which is still considered to be one of the largest in human history. It far surpasses the results of the western "green revolution" - the introduction of artificial fertilizers, mechanization and agricultural poisons - by far. Like the Chinese of today, we can learn from ancient China that through human intelligence and the respectful treatment of nature, a better life is possible without destroying the regionally available resources.
The exchange of goods between China and Europe was once shaped by the trade in silk. However, knowledge rarely migrated between cultures on the Silk Road. Patents did not yet exist, and they could not have been enforced without international jurisdiction and rapid communication. Knowledge and knowledge were nevertheless defended as part of national sovereignty; they were kept secret, and that was all the more true of peasant knowledge. But today the time should be ripe to share the experience of turning deserted land into fertile soil. It makes much more sense to pass on and develop this knowledge among the world's farmers than to export weapons and wage wars for resources. Soil fertility is key to the development of civilizations. All high cultures considered it the foundation of survival. All civilizations of history that did not succeed in specifically generating humus from organic waste and enriching it in the soil in order to transform hostile regions into blooming landscapes have finally perished.
The macroeconomic benefits of fertile soils go far beyond food production. Fertile, humus-rich soils with strong biomass growth are probably the decisive way to remove sufficient carbon dioxide from the atmosphere, to store carbon in the soil, to positively influence the regional water balance and to produce high-quality industrial raw materials in a way that is suitable for grandchildren without destroying nature.
Natural silk versus artificial silk
Even if we encounter silk in numerous textiles by name, world production of natural silk has fallen by 85 percent in the last 100 years and has been replaced by artificial silk made from petroleum.
In 1900 the annual world production of natural silk was one million tons, today only 135,000 tons are produced. Around 25 million jobs were lost as a result. Today, natural silk is almost only produced in India, China, Japan, Brazil and Thailand. The need for mulberry trees could quickly rise again if the demand for natural silk for innovative products in medicine, for cosmetic products or to replace stainless steel and titanium alloys grows.
Thanks to the pioneering work of Fritz Vollrath, Professor at the University of Oxford, it is already possible today, for example, to produce silk threads with very different properties from silk protein using different process conditions - pressure, temperature, humidity and enzymes. Spider threads serve as a model. A completely new type of bio-based products is created without high energy requirements and without substances that are harmful to the environment or health, such as chlorine, caustic alkalis, acids or other toxic auxiliaries. Petroleum-based polymers could increasingly be substituted by bio-based polymers made from silk.
It is estimated that around 500,000 hectares of mulberry trees would have to be planted for a realistic increase in the demand for silk for non-textile purposes by one million tons. At costs of around 2000 euros per hectare, an estimated two million jobs could be generated. In the biomass of these newly planted trees alone, 20 million tons of carbon could be stored annually, which corresponds to around 10 percent of Germany's greenhouse gas emissions. In addition, there would be nine million tons of silkworm compost annually and one million tons of biochar from the branches, which could increase the humus content on the 500,000 hectares by 0.2 percent annually. This build-up of humus would absorb the equivalent of another five million tons of greenhouse gases in the soil. Since mulberry trees are particularly suitable for agroforestry systems and potatoes, ginger, beans, corn, cabbage, pumpkin and many other crops thrive excellently among the trees, the overall effect in terms of carbon storage as well as economic efficiency and ecosystem services is much higher.
The renaissance of the mulberry trees
So may the mulberry trees not become monocultures, but part of biodiverse agroforestry systems that store carbon and water, make soils fertile, and produce food and valuable bio-based raw materials! In Switzerland there is already an association of manufacturers of natural silk - and there are new mulberry trees on former pastures. A start was also made in Nepal in the months following the great earthquake. In a village between Kathmandu and Pokhara, the residents have jointly decided to plant 10,000 trees on the abandoned terraces in the area. So the soil is protected from erosion, drinking water is filtered and stored, habitat for bees and countless tropical insects is created, humus is built up and carbon is stored. In addition to wood for building, cooking and biochar fertilizer, the trees will provide animal feed, essential oils, medicines, fruits and silk from next year - because a third of the trees planted are mulberry trees. \ \ \
This article was originally published on the recommended pages of www.ithaka-journal.net. We would like to thank the editors of the »Journal for Ecology, Viticulture and Climate Farming« for the kind permission to reprint.
(61) is an economist and entrepreneur. In 1994 he was appointed to the United Nations University in Tokyo to prepare the Kyoto Protocol. There he co-initiated the “Zero Emissions Research Initiative (ZERI)”, which he still heads today.
holds a PhD in soil science, worked for a long time at the Federal Ministry for the Environment and is one of the pioneers in the implementation of closed material cycles in urban and semi-urban areas. He holds workshops and lectures on terra preta culture.
Silk in Switzerland:
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