Severe night frosts are expected throughout Italy, but there are those who have been using anti-frost irrigation since 2003. This is the case of Stefano Rivalta, a farmer in the province of Ravenna. And he is very satisfied with the active protection implemented.
"I have 23 hectares of peach orchard, with underground drainage and all protected by the anti-frost irrigation below the foliage. I used the system last week, when the temperature dropped below 3°C below zero. I started the system at 9:40 pm and then I unplugged it at 8 am".
Ice formed during below-foliage irrigation (from the Rivalta archive)
The weather forecast gives us an idea about the frosts, but every farmer knows that there is a lot of difference between different zones, sometimes even within the same area. Rivalta uses a scientific method which, until now, has always allowed him to accurately forecast if there will be a frost.
"First of all, it is necessary to have a professional thermometer, placed in a weather shed and not directly affected by sunlight. To know what the minimum temperature will be the next morning, it is necessary to detect the temperature of the dry bulb (TA), that of the wet bulb (TB) and apply the following formula: TA + ((TB - TA) - VF) = minimum temperature. VF, a fixed value, is equal to 8 with relative humidity greater than 40%, or equal to 10 with relative humidity less than 40%. The margin of error is around half a degree, and the temperatures must be measured at sunset, for maximum accuracy. This has been my experience in over twenty years and I always had excellent results".
Rivalta has a long experience in active anti-frost protection and, at the turn of the 2000s, was part of the Emilia Romagna region's team for experimentation in this sector. His system has below-foliage sprinklers with 5x5 meters spacing, equal to 400 sprinklers per hectare, and a rainfall of 32 cubic meters per hour.
"In the absence of below-foliage irrigation, I have had excellent results with the hose reel as well. In my peach orchard I have both grassing and pruning residues. This allows me to increase the surface on which the water stops and passes from liquid to solid state, generating the heat necessary to preserve the plants".