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Circular Knitting

Heating textiles for use in plant cultivation

The heating elements can be used to control the vegetative phase very accurately to optimise the harvest, the Institute reports.

14th August 2014

Knitting Industry
 |  Boennigheim

Technical Textiles

By the year 2050 there will be about 9.2 billion people living on the Earth – around 2 billion more than today, according to the latest estimates.

In order to be able to secure food supplies in the light of this rapid increase, scientists around the world are looking for innovative solutions for the agricultural industry.

The heating elements can be used to control the vegetative phase very accurately to optimise the harvest. © Hohenstein Institute

Among them are the scientists at the Hohenstein Institute, who, together with the circular knitter roma-Strickstoff-Fabrik Rolf Mayer and the State College of Horticulture and Agriculture, have developed heating textiles for use in plant cultivation. These are placed around the roots of the plants and so supply them with targeted warmth.

Heating textiles

The temperature around the roots is a crucial factor in germination (seeds), sprouting (bulbs), plant development (generative phase) and plant growth (vegetative phase). That is why, when these high-tech textiles are used in the greenhouse, they help save energy, because the ambient temperature can be greatly lowered with no reduction in yield.

The textiles being developed needed to have a stable temperature profile, permit variable heating from about 5 0C to 40 0C, be structurally resilient and water-resistant and not degrade in soil. © Hohenstein Institute

The heating elements can be used to control the vegetative phase very accurately to optimise the harvest, the Institute reports. Last but not least, because the heating textiles provide safe and reliable frost protection, they are said to enable more tender plants to be grown even in difficult climatic conditions.

Meeting requirements

The research project was based on an extensive list of specifications in order to meet the various requirements. Among other things, the textiles being developed needed to have a stable temperature profile, permit variable heating from about 50C to 400C, be structurally resilient and water-resistant and not degrade in soil (anti-fouling).

The Hohenstein researchers paid particular attention to analysing the heating capability of the textiles. This was studied in relation to the germination behaviour of the trial plants. © Hohenstein Institute

To achieve these objectives, the project partners investigated the suitability of various circular knitted heating fabrics.

The basic material for the fibres was always polyester, in once case galvanised with silver to make it conduct electricity. In a second material, conductivity was achieved by knitting a stainless steel yarn into the fabric. In the third test material, two stainless steel threads entwined in a criss-cross pattern provided the electrical conductor.

Field trials in an all-weather greenhouse after 14 weeks of heating Pelargoniums Left and centre: heated, Right: unheated © Hohenstein Institute

The three fabrics were subjected to various textile technology tests at the Hohenstein Institute that included not only mechanical stress testing but also tests to assess the resistance of the textile to destruction by microorganisms.

Experimental greenhouses

On the basis of this work, in the winter of 2012/13 the researchers from the State College of Horticulture and Agriculture put the heating textiles into use in various experimental greenhouses. Alongside the functional analysis of germination behaviour and plant growth, the main focus of these practical tests was on possible negative influences, e.g. from plant fertilisers used in so-called ebb-and-flow hydroponics systems. During the first trials, the researchers had problems with salt deposits and corrosion of the heating textiles.

The heating capability of the textiles that were being developed was tested in real-life conditions. © Hohenstein Institute

The following winter, more experiments were carried out in real-life conditions. To alleviate the problems, the textiles had been specially modified: the researchers tested the suitability of coating films based on wax, latex, silicon and polyurethane. The polyurethane film proved to be the best at preventing the deposits of salts that caused the material to corrode. Plants with the benefit of underfloor heating grew significantly better than the comparison specimens, in all test conditions. The energy consumption was also measured.

www.hohenstein.de

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