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To the farmer – rational defrosting plant

In the municipality of Fondi, as for the large part of the Pontine Plain, during the winter is customary to utilise the “hot” groundwater in order to keep “warm” the greenhouses, by flowing or sprinkling the roof when the temperature nears to 0°C. The so called “idroserra” (hydro-greenhouse) was invented in Fondi in the first 70ies by two researchers from Salerno (Porcelli, Amore). It spread quickly all over the Pontine Plain and actually it is esteemed that it covers an area of more than 1200-1400 hectares. It is clear that it has an huge environmental impact, because it is calculated that the underground water consumption for this defrosting utilisation overcomes largely the crop irrigation consumption during the hot season, even referring to the more water-requesting crops. It is esteemed a yearly underground water global consumption for defrosting of about 15.7 millions of litres/hectare. It is obvious that this “method”, because of its enormous environmental impact, brings evident stress to the groundwater system, due to the uncontrolled water drainage from private wells of the different farmers.

During a survey concerning the behaviour of the local farmers, it came out that a very high percent of these latter starts the defrosting device even when there is no real danger, for different motivations:
- wrong evaluation of frosting risk;
- scarce attention to the calibration of the instruments of control inside the greenhouse;
- scarce utilisation of technologies apt to mitigate low temperatures (textile covers);
- utilisation of flowing instead of other systems with better performances;
- scarce or absent scientific knowledge upon the different performance degrees of sprinkling systems and of different micro-irrigators typologies .

All this is confirmed by the fact that the drainage of underground water is freely allowed and for the farmers the only restricting element is due to the energy cost for the water pumps (electric energy or diesel fuel for the engines).

It is esteemed that the defrosting methods actually utilised (through micro-irrigation spray sprinklers or polyethylene micro drilled pipes Sbrinex) have an average consumption values per hectare as follows:

Water

volumes per minute

m3/(minute x ha)

Number of our

of operation

of the plant
Global volume

per hectare

per year(m3)
1– 1.5
250
15,000 – 22,500

The solution given thanks to the demonstration model, proposed a) to create a short circuit to recycle water; b) to utilise a more efficient system for water sprinkling (spray sprinklers at 360° instead of Sbrinex drilled pipe); c) to adopt a thermic screen in order to mitigate the temperature falls inside the greenhouse.

Sbrinex pipe
Spray 360° sprinklers

Although the demonstration with the short-circuit system was not completely satisfying (perhaps because the reservoir dimension was too small), the adoption of 360° spray sprinklers helped to reduce of more than 20% the use of water. This solution technically easy and quite economic brought a save to the farmer and an environmental benefit of interest.
But the more interesting technical innovation was individuated in the thermic screen. It is a kind of perforated tissue made of alternated strips of aluminium and transparent plastic waved on natural cotton thread. There are different kinds of tissue, because by varying the number of aluminium and plastic strips it is possible to obtain different thermic-shading properties. If for instance the number of plastic transparent stripes is augmented, the thermic action is reduced, and on the contrary if are augmented the aluminium stripes. For SUSTGREENHOUSE demonstration, an intermediate kind was adopted, named PH 55 FP, made by BONAR BV (Netherlands) company, which gave 55% of shade, UV stabilised, anti-flame, 84 gr/m2 weight.

opening a thermic screen
the screen tissue
thermic screen opened

The screen runs on a rail and is drawn up under the ceiling of the greenhouse when it is too cold or there is too much sunshine. In this way during the night the infra-red rays of the crops are reflected downward and is avoided direct contact with the cold air procuring dew; instead during the hours of excessive sunshine there is a shading effect. The presence of the screen make the practice of “liming” superfluous (the external painting of the greenhouse with lime paint in order to shade the interior during the summer).In fact the reflective property of aluminium enables a reduction of the intense summer shine which otherwise would strike crops, soil and iron structures, with a benefit for the reduction of too high air temperature.

In the trial made on February 2011 the thermo-regulation of the screen gave a reduction of temperature loss caused by radiation starting from the first hours of the night. At 19.00 internal air temperature of the sustainable greenhouse was always higher of 1 – 1.5°C respect to the standard greenhouse. At the end of the night it was 0.6°C higher. This enabled the completely un-utilisation of the defrosting plant into the sustainable greenhouse with an estimated save of 18,500 m3 water/ha.

Globally the utilisation of a thermic screen got an increase of production of 16,25% (on tomato crop). During the daily surveys was detected a sensible decrease of air moisture inside the greenhouse testified by absence of the morning dew on the leaves: This enabled a reduction of the phyto-sanitary treatments against diseases due to fungi or bacteria. For this reason in the sustainable greenhouse in the last crop cycle only 8 pesticides treatments were made instead of 11, with a save in products and accessories of 124,80 € (that is 36,3%) and a save in environmental terms of 3,4 Kg / 1000 m2 of pesticides. It is important to note that cupper application was thus totally avoided, thanks to the fact that there weren’t conditions favourable to bacteria diseases.

 

Defros- ting

Soil  tillage

Water, nitrogen