CRITIC STUDY OVER THE USE OF PLASTIC GREENHOUSES FOR FLOWER CROPS AT THE PROVINCE OF BARCELONA (SPAIN).
The main reason to start the use of plastic structures has been the need to protect crops from the light frosts that have been appearing in these last years but there has also influenced the fact that every day it is increasing the demand of better quality.
The convenience of not delaying supplies to the markets during the most appropriated commercial periods and the need of obtaining products of more selected characteristics have been noticed specially in carnations for exportation.
A simple plastic covering or ceiling may already be enough to save the growing of the carnation from damages originated by the light fall below zero that use to appear. Moreover there are obtained other direct and indirect profits.
Thus, in the "protection" chapter, it is avoided the abrasive action of wind and the noxious effects caused by dews (diffusion of criptogamic diseases, aggrieve frost damages, transport difficulties and preservation of cut flowers). Considering other sights as "cultural technics" there are also better incomes, for instance during the raining season, because it may be carried on the pesticide treatments, the cleaning of the plant and the clearing of flowers and even to keep a better control of the mineral nutrition in the habitual light soils. All of this of course reflects in a better "quality", but the covering itself gives positive results as well. The SIM varieties are those obtaining more profits. The whole plant acquires better esthetic qualities specially in the stem: larger and elegant length, flexibility, more separation between nodes, crimp leafs and colouring. Less advantages are obtained in the flower but nevertheless the colouring of petals is undoubtedly increased.
Causes are quite complex and must be a consequence of the better average thermic level in the air and in the soil, the protection against wind and some forms of adverse moisture, as well as associated effects of nutrition and control of pathogen agents.
The plastic greenhouse closed, due to its higher cost and specially because of a more complicated and delicate handling have been substituted almost totally in the growing of carnation by the mentioned simple covering without lateral closing. The greatest advantages that can be obtained-from a closed structure are diminished by the damages that can appear because of a defficient handling, as it happens in the case of larger thermic falls and internal dews that so often appears.
Plastic structures for roses with an isolation more or less complete are being adapted though there can be already appreciated the advantages over the crop without protection (forcing).
Several types of structures have been diffuse, all of them more or less limited to the superior covering and generally inspired in foreign patterns (specially french and italian). Numerous tests achieved by floriculturists have given as a result the development of some models with original characteristics.
The plastic film is extended over a support frame generally made out of pine, chestnut-tree or acacia.
The enemies of these coverings are wind and sun radiation. The wind causes damages which go from loosening the film and breaking it to the total destruction of the installation.
The sun radiation may cause a more or less quick degradation of the plastic, with progressive lost of its physic properties such as: transparency, flexibility and mechanic resistance, in general.
Both sights have conditioned first the drawings, which have been improved according