Straw

The term straw ( this, - [ e] s, not plural) is a collective term for threshed and dry stalks / stems and leaves of cereals, oil crops, fiber crops or legumes.

Most straw is incorporated as soil organic matter and nutrient source in the soil of agricultural land, either immediately after harvest or - mixed with animal excrement as manure - after it was used as bedding. Some types of straw also serve as raw fiber, but low in nutrients feed. Straw is also used energetically as fuel and as a raw material for synthetic biofuels. In addition, straw as a building material ( straw bale ), as raw material for (art) manual skills used (eg straw-plaiting ) and formerly known as the material for covering of roofs.

Unlike straw is threshed hay not, dried, cut forage, that is mostly of grasses and herbs, for example, from Clover.

Use

Straw can be used both materially and energetically. Here, the use of the straw to the prehistoric periods of human history can be traced back to the beginnings of agricultural use of cereals. The straw of different cereals, mainly wheat, rye, barley and triticale, is obtained as a by-product in the use of cereals for food and starch. In about 23 million tonnes of wheat produced in Germany hectares to 3.2 million, added 11.5 million tonnes of barley to 2 million ha, 2.8 million tonnes of rye to 550,000 ha, 2.6 million tonnes of triticale to 380,000 ha and 1.2 million tonnes of oats on 210,000 ha So fall each year about 21 million tonnes of cereal straw on which 11 million tonnes of wheat, 6.5 million tonnes of barley, 2 million t rye, 1.3 million tonnes (calculated on the basis of grain - straw ratio ) oat and 1.2 million tonnes triticale straw. Of these can be found in the material cycle for energy or material use without damage to the soil fertility around 20-30 %, otherwise a comparable supply of organic matter to the acreage is necessary to ensure a balanced humus balance.

Material use

Bedding and horticultural use

Most of the retracted straw is used as animal bedding for large livestock (cattle, horses and pigs ) and is returned to the nutrient cycle after using them again. In the private sector straw is used for the keeping of rabbits and other small animals: It can be used as an alternative to wood shavings or scrapings here. Barley straw has a much lighter color over straw from other cereals and poor absorbs moisture. For this reason it is not as good as bedding. The same is true with oat straw, which is also very soft and is therefore mainly used as feed straw. Rye and wheat straw, however, are suitable for feeding as well as litter. Lesser amounts of straw used in mushroom cultivation as Aufzuchtssubtrat or in orchards, especially in strawberries for inferiority of fruits, so that the fruit does not rest on the ground and pollute. It also serves as a protection against the cold.

Construction and insulation

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A material used mainly wheat straw makes its use as a construction and insulation dar. in house construction is established the straw bale building, which was already practiced in the U.S. since about 1890, is experiencing a renaissance since the 1980s, nowadays straw bales are used as building materials in North America, Europe and Asia. When bearing straw bale construction, the walls are made entirely of straw bales and the roof load is carried on the straw bales. In the non - load-bearing construction, a timber framework forms the supporting structure and the spaces ( partitions ) to be filled with straw. This type of construction is largely the timber frame or the traditional half-timbered building, and is usually preferred in Germany, as straw bales are here by the building not yet approved as a load-bearing building materials. Furthermore straw is applied in the form of Strohbauplatten for the purpose of drying Ausbaues.

Straw is a good insulator and has a WLG- value of 046 in ball shape. Expertly built of straw bales are mildew resistant, are considered normal flammable building material (B2 ) categorized and are on a par with setting values ​​of 2.3 % in the component other insulation materials. The bulk density of the bales is between 90 and 150 kg / m³.

In addition there are numerous hybrids. So straw was traditionally often mixed in earth building with clay used, it increases strength and improves the thermal insulation. In addition, straw roofs were made ​​earlier in many regions. Investigate the use of straw in combination with cement as a building material is similar to the plate-shaped wood-wool board.

Other materials production

Above all, historically the use of straw for a number of products had a much greater importance, however, was superseded by other materials. Of woven straw shoes were made, the straw shoes so-called. Another use were beehives of woven straw, which are sometimes still made ​​.

Refit is the use as a drinking straw, although plastic drinking straws are often still referred to as straws. As a packaging material previously straws were used to dampen vibrations. This function is fulfilled primarily by today polystyrene and other plastics, although there are new products based on straw as packaging filler. Sometimes straw is also used for the production of paper .. Also targets for archery are made of straw

In traditional Japan are straw mats made ​​from rice straw ( tatami ), which were placed on the floor, the seat of the People, not chairs or benches. The soil was also to roost By placing multi-layer cotton blankets ( futons ) on this tatami, so that there were no beds in the European sense. In Europe, tatami mats are used inter alia as a base for the practice of judo, and other Japanese martial arts.

For a long time also served in Europe straw as a bed of straw. However, since the long stalks broke quickly, the camp was hard and uncomfortable. Today, the natural product experienced in straw mattresses a small renaissance: Purified straw is baled, surrounded by a fabric, quilted with yarn and often combined with other layers of natural materials such as natural rubber.

In addition to wood, especially fast -growing species from short rotation plantations, cereal straw is a potential supplier of the lignocellulosic biomass as raw material for use in biorefineries for the production of various chemicals platform dar. Corresponding projects are still at the planning stage.

Energy Use

Combustion

Straw is released in Germany in accordance with the small combustion regulation as a standard fuel for heating between 15 kW and 100 kW, so that a burning in plants is permitted for home use without a special permit. For plants, for example, 15 to 50 kW resulting from this rule emission limits (per m³ gas) of 0.15 g / m³ dust and 4 g / m³ carbon monoxide (CO), the use in heating systems for individual households, however, is not widespread because the system technology compared to other fuels (pellets, wood) is more complex. In Denmark the burning of straw to decentralized heat and power production is already relatively widespread. In northern Germany the first three straw heating plants in Germany are planned, the rated thermal input should be 49.8 MW each. It is to be distinguished thereby from the combustion grain, wherein the grain is used for the firing. The production of energy from straw pellets for combustion is practiced sporadically, but most are only suitable for pellet wood pellets.

The combustion properties of straw differ significantly from those of the fuel wood. Among other things, the ash contents are significantly higher, at the same time reduced ash melting point and higher airborne dust emissions. In addition, the concentrations of nitrogen, sulfur and chlorine are less favorable for combustion. Especially in small systems comply with applicable emission limits, considerable additional expense is connected. It has a calorific value from 18.3 to 18.5 MJ / kg.

Liquid fuels

As cellulose -rich raw material straw is also suitable for the production of biofuels, the cellulose used as a starting material (eg BtL fuel and other synthetic biofuels, cellulosic ethanol). These fuels are still largely in the development phase.

Biomethane

2012 was taken into Zoerbig (Saxony- Anhalt), the first plant in operation, capable of producing biomethane from annually 20,000 tons of straw. The German Biomass Research Centre in Leipzig estimates the potential in Germany on 8-13 million tons, in Eastern Europe to 240 million tonnes, with 8 million tons 2.5 gigawatt or clear the energy requirement of 4 million natural gas vehicles equivalent. Unlike the cultivation of energy crops due to the energetic use of straw is no competition for land for food production. Since the digestion residues can be spread on the fields, no nutrient loss occurs.

Etymology

Etymologically, the term depends straw along with the Old and Middle High German stro expression ( scatter ), actually means Fully sprinkled or Spreading. Another term for straw is Strüh and can be found in the Rhenish dialect.