Frost protection irrigation
When frost protection irrigation refers to the targeted spraying of crops in orchards , vineyards and vegetable growing and in nurseries with very fine water droplets. When the distributed water freezes, heat of crystallization is released on the plants , so that leaves and flowers are usually protected from frost damage. The aim is to protect the plants in the event of frost during the vegetation period and thus to avoid later crop failures. Frost protection irrigation is used especially in spring when the fruit is in bloom and when growing frost-sensitive crops such as strawberries or new potatoes.
functionality
If the air temperature falls below 0.5 ° C, uninterrupted irrigation begins, which causes a growing layer of ice to form on the frost-sensitive parts of the plant . The irrigation is carried out by sprinklers (e.g. circular sprinklers ) which spray over a large area and produce fine droplets and wet the above-ground parts of the plants . When the water mist freezes, the solidification heat of the water is released - about 335 kJ per liter of water - so that the temperature inside the ice envelope does not drop below freezing point. Particularly in late night frosts, this can prevent the sensitive flowers from freezing to death during critical hours. After sunrise, the heat of the sun thaws the ice sheet again. A small proportion of the heat supply takes place via the surface tension, because the atomization of the water requires pressure energy, which is then stored in the surface tension of the microdroplets; if the microdroplets combine to form larger droplets, this stored energy is also released in the form of heat that is absorbed by the buds. In the fine droplets, oxygen dissolves better and freezing microdroplets include additional air bubbles one, creating a thermal insulation effect by so-called loose rime ice formed.
Some insensitive plant species can be protected against frost damage by irrigation at air temperatures down to the range of −9 ° C.
restrictions
A sufficient protective effect through the solidification heat can only be achieved if the relative humidity is at least 60% and the wind speed is below 3 Beaufort . Otherwise more energy will be withdrawn from the plant by evaporation heat than heat is given off by the freezing process. The evaporation cooling at a temperature of 0 ° C is approx. 2498 kJ per liter of water.
This opposite, additional cooling effect also occurs if the continuous irrigation is interrupted when the frost is still persistent. For the frost protection irrigation to be successful, it is therefore necessary to continue irrigation until a positive ambient temperature has been reached and the ice on the plants has completely thawed. In the event of prolonged frost, there is a risk of ice breaking due to the freezing irrigation water in fruit trees and bush fruits.
Problems
Frost protection irrigation is still considered to be the safest way to protect flowers from frost. However, depending on the degree of frost, between 20,000 and 50,000 liters of water per hour and hectare are required, which can lead to the soil becoming soaked. This inhibits the root activities of the plants and increases their susceptibility to diseases. In addition, nutrients can be washed out and the drivability of the soil restricted.
Alternatives
Alternative methods are listed under frost protection .
swell
- http://www.lid.ch/fileadmin/user_upload/lid/infoservices/2661/Md2661.pdf
- Ulrich Sachweh (editor): The gardener, volume 3, tree nursery, fruit growing, seed growing, vegetable growing . 2nd edition, Ulmer, Stuttgart 1986/1989, ISBN 3-8001-1148-9 , pp. 80, 283 f.
- Ulrich Sachweh (Editor): The Gardener, Volume 1, Basics of Horticulture . 5th edition, Ulmer, Stuttgart 1984, 2001, ISBN 3-8001-1184-5 , p. 480 f.
- Dirk Köpcke: Successful frost protection taking into account the thermodynamic processes in orchards, 2012, Mitteilungen des Obstbauversuchsring des Alten Landes eV, pp. 136–143 ( http://www.esteburg.de/service/mitteilungen-des-obstbauversuchsringes/archiv/did_2267544 .html )
Individual evidence
- ↑ Archive link ( Memento of the original dated February 9, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
