GB2531749A - Photoselective fabric for horticulture - Google Patents

Abstract

Horticultural shading such as netting that comprises black areas interspersed with areas of other colours, such areas preferably being stripes or other patterns. The other colours are selected from white, yellow and/or blue. The various coloured areas are selected for their qualities relating to reduction of infrared and UV light, scattering of visible light, modifying insect behaviour and the transmission of red and blue light to the plants.

Description

Photoselective fabric for horticulture

Technical Field

The present invention relates to shading for use in horticulture, especially shading used in connection with growing crops in an enclosed space. The shading may be netting.

Prior Art

Known greenhouses and shade houses use a variety of materials to modify the transmission of solar radiation. Glass is the most well known as it transmits visible light well but prevents the radiation of heat -' the greenhouse effect'. Polythene is commonly used for the same purpose and results in a cheaper but less durable solution.

However, in hot, sunny climates, it is desirable to reduce temperatures, rather than to trap the heat, and this is commonly achieved with evaporative cooling, e.g. using a greenhouse with an evaporator at one end and a fan at the other., which is also known as 'pad and fan' technique. A company, Seawater Greenhouse Limited has pioneered the use of seawater, rather than fresh water for this process (see www.seawatergreenhouse.com).

However, such 'pad and fan' solutions use greenhouse structures -covered in glass or plastic to act as wind tunnels, to trap and retain the cooler and more humid air. As a consequence, the air tends to heat up as it travels from the pad to the fan. This temperature gain limits the effective length of the tunnel to around 40m.

An alternative solution is simply to grow crops under the protection of a shade fabric which reduces solar gain by any given %. As a fabric is not airtight, there is no advantage of using fans to draw air along a tunnel made of the fabric, so pad and fan solutions are usually not employed with shade systems.

We have discovered through trials and verified with a considerable amount of CFD and numerical modelling that in most locations, there is sufficiently strong prevailing wind to drive the evaporative cooling process directly, without the need for fans, and that this cooling effect is retained within a shade structure, largely because cooler air is denser and tends to sink and it is drawn through a greenhouse by the positive pressure at the windward end, and negative pressure at the lee end.

Shade nets are available in a very wide range of colours and densities or % transmission and they are commonly used for crop cultivation in hot climates, especially Mexico, Israel, China and the Middle East. They are made to serve a specific function, either to: 1 Transmit a specific fraction of light -anywhere from 10% to 90% 2 Transmit a specific colour, often red, green, yellow or blue to modify the photosynthetic response of the plant, or 3 Prevent to passage of pests, birds or insects.

4 Diffuse and scatter light, such that direct solar radiation penetrates the plant canopy Provide a degree of wind protection Disclosure of the Invention The present invention provides improved horticultural shading for use either in greenhouses or in other enclosures or for use outside, for example suspended above a crop.

According to the present invention, there is provided a horticultural shading comprising areas of black interspersed with areas of white and/or yellow / blue.

The shading may include holes or pores (and generally will include such holes or pores when in the form of netting), in which case it is the material between these holes/pores that bears the black, white or any other colour. The overall percentage of the shading that is made up of holes/ pores can vary widely according to degree of shading required, e.g. pores can make up 10% to 90% of the shading surface area. The holes or pores may allow air to pass. The shading may be a woven, knitted or non-woven netting material and the nature of the weave will generally dictate the area that is made up of the holes or pores. Alternatively, the shading may be a continuous sheet bearing the black/white/yellow colours; the sheet may be continuous, e.g. a glass or plastic panel, or may include holes or pores.

Specifically, black shading areas are the most effective provider of shade, reducing solar radiation transmitted to a crop while allowing a relatively large passage of air to pass through it. --Black shading requires less material to achieve a given shade % value and it tends to be the cheapest and most durable as carbon black, which can used to provide the black colour, provides a good UV block.

White shading areas provide the best scattering of light, ensuring direct sunlight penetrates further into the plants.

Black and white stripes or patterns, as employed by zebras, some cows, goats and sheep are known to confuse and deter certain flies and other insects. Yellow and blue are also known to attract certain insects, and when they land on a yellow net they get confused by the shading pattern and so at least a portion of them starve and die. Yellow also scatters incident light.

Thus the areas may be (a) black-and-white or (b) black and yellow / blue or (c) most preferably, black, white and yellow / blue. The areas may be of any shape, although, in one embodiment, they are elongated so as to form stripes. These stripes need not be evenly spaced and indeed the stripes of one colour may merge with stripes of another or the same colour, for example in the manner of the stripes on a zebra. A stripe need not be of a single continuous colour along all of its length and, for example, a single stripe may be white along part of its length and yellow along the remainder.

The terms "white", "yellow" and "black" are used to denote the colours as perceived by the human eye. Obviously, the black colour may be a very dark colour that is perceived as being black or almost black. The white colour may be an "off white" colour, such as cream. The usual definition of "yellow" is radiation having a wavelength within the range of 570 and 590 nanometers. However, that does not preclude the presence of other wavelength bands within the yellow colour so long as the overall perception is that the colour is yellow. Insects are known to be attracted to infrared and/or ultraviolet radiation and the yellow colour may be to reflect or transmit such invisible IR and UV radiation.

The shading may include areas of other colours, although it is preferable that it should be largely made up of the areas of black/white/yellow colours, for example at least 80% of the shading (by area) is made up of the black/white/yellow colours, e.g. at least 90%, and in one embodiment, the shading is substantially made up of the areas of black/white/yellow colours.

The black, white and yellow / blue colours may each form at least 20% of the area of the shading Plants, being green, reflect green light, and absorb preferentially the light in the red and blue ends of the visible spectrum -known as PAR or Photosynthetically Active Radiation and light in these wavelengths will mostly be provided by light that has passed through pores in the shading and by light scattered from the white areas of the shading but some will also be provided by the yellow areas. The shading should preferably be such that it allows PAR radiation to pass through it in the red and blue ends of the spectrum while blocking green combined, or white light minus green appears pink to the human eye.

Around 50% of the energy in sunlight is in the infrared band. It is is invisible to the human eye and does not contribute substantially to photosynthesis. Excess heat translates to excess transpiration, stomata! closure and reduced photosynthesis. The shading therefore preferably will block (absorb and/or reflect) some or all of incident infrared radiation.

Around 5% of the energy in sunlight is in the UV band, again invisible to the human eye and not considered to be a component of PAR, although UV does have some subtle influence on chemical development in plants and influences taste. It is also used by pollinating bees for example to navigate. The shading therefore may be such that it will allow some of incident UV radiation to pass through it.

In summary, an ideal shading is a netting fabric that provides a combination of stripes or patterns to: 1 Block the transmission of infrared (black) 2 Scatter visible light and confuse insects (white and yellow / blue) 3 Allow the selective transmission of red and blue to plants 4 Allow some transmission of, but be unaffected by, UV.

All polymers commonly used for net fabrics as well as greenhouse films, such as polythene, PVC, polycarbonate etc. are degraded by UV, giving them a short life in very sunny climates. Polythene may last 6 years or more in the UK, 2 years or less in the Middle East. Black net is the most durable but still only last 4-8 years. Nets made from glass fabrics are very much more durable and therefore are preferred. They are used on large architectural type canopies, (e.g. the 02 Dome in London) and the glass in the fabric can be made in any colour and last indefinitely. Glass fabrics are commonly used in high performance applications but not for horticulture.

Claims (10)

1. CLAIMS1. Horticultural shading, e.g netting, comprising black areas interspersed with areas of white and/or yellow / blue.
2. 2. Horticultural shading as claimed in claim 1, which includes white and yellow / blue areas, with the coloured areas being interspersed between the white and all black areas.
3. 3. Horticultural shading is claimed in claim 1 or claim 2, wherein the black areas are elongated, e.g. in the form of stripes or patterns.
4. 4. Horticultural shading as claimed in any preceding claim wherein the white and/or yellow areas are elongated, e.g. in the form of stripes or patterns.
5. 5. Horticultural shading as claimed in any preceding claim wherein the black areas block a large fraction (by energy) of the incident infrared radiation.
6. 6. Horticultural shading as claimed in any preceding claim wherein the white and coloured areas scatter visible light
7. 7. Horticultural shading as claimed in any preceding claim wherein the coloured areas alter the behaviour insects, such as confusing them.
8. 8. Horticultural shading as claimed in any preceding claim that allows the selective transmission of red and blue to plants.
9. 9. Horticultural shading as claimed in any preceding claim that allows some transmission of, but be unaffected by, UV.
10. 10. A method of growing plants comprising shading them from sunlight by horticultural shading as claimed in any preceding claim.