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In the Finnish fertilizer program, a special hopper slung under the helicopter is fitted with a small diesel motor, controlled by the pilot, which throws the dry fertilizer out centrifugally.|

The Finnish forest industry has confirmed pretty much what every gardener knows: The best way to manage your crop is to fertilize it—and they are doing exactly that with their trees, expecting some good gains in timber volume.

By Alan Froome

It probably comes as no surprise to anyone with a green thumb, but the Ministry of Forests in Finland has stated that the best thing managers can do for their forests is to fertilize them. This is after independent scientists have proved that bigger and better trees result from spraying fertilizer.

Government sources stated that forest fertilization is the most profitable thing a forest owner can do and taking the lead, ordered sufficient fertilizer to spray 36,000 hectares of state-owned forest in 2007. They plan to increase this to 100,000 hectares in future years and predict that a single application of fertilizer on this area will increase the wood availability by 1.5 to 2 million cubic metres. They also claim there are less defects in the wood.

The senior scientist at Metla, Finland’s largest forest research organization, endorses the program and says he anticipated 15 to 20 per cent improved tree growth after seven to eight years of aerial fertilization. “The lower sawlog part of the tree actually grows faster after fertilization than the upper pulp-wood section, a further value advantage.”

Note that in Finland, standard practice is to use only the larger lower part of the tree for sawlogs, with the upper part of the same tree going for pulp-wood. Typically, the value of the sawlog section is three times the value of the upper pulpwood section of the tree.

To provide a bit of background, Finland has the largest forest in Europe with 76 per cent of its area covered by trees, primarily coniferous. Some 20 per cent of the country’s exports are from the forest industry. No less than 60 per cent of the forest is privately owned and most of this is in small parcels, 10 to 30 hectares being typical for the 300,000 or so owners. About 26 per cent is state owned and the rest is owned by big companies like Stora Enso and UPM.

Most private owners are members of an organization called Metsanhoitoyhdistys (roughly translated as Forest Maintenance Society), which also promotes the use of fertilizer and actively contacts their members to co-ordinate fertilization programs in different regions of the country.

Ground level spraying is sometimes used for the smaller areas, but aerial spraying by helicopter is preferred on areas 20 hectares and larger. To keep the cost down, the usual approach is to get groups of owners with adjacent forestland to order helicopter spraying over their combined area.

The two principal companies involved so far in the helicopter fertilization program in Finland are GrowHow, a division of Kemira Oy, which supplies the chemicals, and Helitour Oy which provides the helicopters.

Petri Kortejarvi, sales manager at GrowHow, describes the program. He says they have developed eight separate chemical mixes to suit different regions of the country. The main ingredients are nitrogen, potash and phosphate, but several other chemicals are added depending on local needs.

For example, tree defects in one region of Norway spruce, indicated by yellow tree-tops, have been successfully corrected by adding boron to the mix. Kortejarvi says that GrowHow feels the best results come from fertilizing every five years, but it’s recommended at least once every 10 years.

For ground spraying, a regular farm tractor type spreader is used, driven between the trees. For the aerial method, the fertilizer is supplied to the job site in 650-kilogram sacks, each of which comprises one lift for the helicopters used. At present, Helitour Oy is the only company contracted to do the aerial spraying, or spreading as it perhaps should be called, as the fertilizer is in dry granular form. Of the 36,000 hectares fertilized in 2007, 30,000 were sprayed by helicopter.

Helitour is based near Tampere and uses Bell 204 helicopters for the work. The spray team comprises four people on the ground, with two trucks carrying the fertilizer to save time and servicing two landing sites at a time, plus two pilots to fly the helicopter. Each pilot is allowed to fly for six hours.

A special hopper slung under the helicopter is fitted with a small diesel motor, controlled by the pilot, which throws the fertilizer out centrifugally. “We find it best to spread the fertilizer after the first thinning, when our trees are nearly 50 years old,” Kortejarvi explains. “The helicopter flies about 30 metres above the tree tops and covers a series of 30-metre wide, parallel paths over the area.”

Kortejarvi says that precise maps are used, along with a GPS navigation system, to tell the pilot exactly where and when to spray. It has to be very accurately done to avoid lakes and streams.

For practical purposes, a landing site to pick up the chemicals should be a maximum of two kilometres from the spray zone and it should be at least 60 metres in diameter. Typically seven or eight landing sites may be used when working in a large area, with the ground crews moving the bags of fertilizer to the site nearest to the spray zone.

Aerial spreading cannot be carried out in windy conditions and when snow is on the ground, which means from mid-October to April in most of Finland.

The big question, of course, is how much does it cost and what’s the payback? GrowHow says that current costs in Finland for the chemicals alone are 60 to 100 euros ($90 to $150) per hectare. This rises to between 240 and 280 euros ($360 to $420) per hectare in total for chemicals, labour and helicopter costs. The payback for the forest owner after six years, however, according to the experts, is in the region of 20 per cent more wood and higher value wood, plus the trees can be harvested earlier. It does seem to be—as the Finns say—the best thing you can do for your forest.