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Soil as one of the principal environmental components represents a complex system consisting of mineral and organic compounds and of living organisms that are in permanent interactions. This means that any negative intervention, either of mechanical or chemical nature, can have deteriorating, damaging or even destructive consequences.


It is well known that a continuous production of immissions represents one of the most serious anthropogenous impacts on forest soils and results in marked changes in both physical and chemical properties of soil. Very often it is possible to observe more and more significant negative changes in reserves of essential nutrients in soil. Acid rains cause a permanent acidification of soil environment, a gradual release and/or leaching of basic elements and, therefore, also a marked deterioration of soil fertility. As mentioned by Pavlenda (1999), acid depositions result in a wash-off of bases (K, Mg) from soil. All these factors show a very negative effect on fertility of forest soils and for that reason it is necessary to take ameliorative measures. Fertilisation represents a very significant intervention of this type. Reasons for application of fertilisers in forest soil were mentioned by Materna (1999) as follows:

  • Forest ecosystems are continuously deprived of great amounts of biogenic elements without any compensation;
  • Since the second half of the last century, forest soils of Central Europe have been contaminated with acid immissions containing great amounts of sulphur and, therefore, also protons. The amount of immissions was estimated to as much as 6,000 kg/ha and it is clear that this caused a further significant deterioration of soil fertility.
  • At present, forest soils in Slovakia and other Central European countries are very to extremely acid and with a low content of calcium, magnesium, potassium and, in some localities, also phosphorus and trace elements.
  • Mineral nutrition of our forest stands is negatively influenced by deficits of magnesium, calcium, some trace elements and, on large areas, also nitrogen. This deficiency is manifested not only in elder forest stands but also in young cultures established now on large areas.
  • Disturbances of mineral supply are very important especially in higher altitudes.
  • The organic (humus) horizon of forest stands contains relatively great amounts of nutrients; however, the bioavalability of these elements is relatively low and the rate of their mineralisation is inhibited above all by extreme acidity of soil as well as by negative effects of immissions of heavy metals, risk elements etc.


For the time being, a supplementary fertilisation of forest stands is more and more important not only on soils with reduced fertility but also when reforesting territories affected by immissions and in regions with finished amelioration works. Growth and vitality of young trees should be increased especially immediately after planting. Regarding the expected climatic changes, it is very important to increase the stability of forest stands through a higher proportion of deciduous tree species; however, they require an increased supply of nutrients than conifers and for that reason it is necessary to pay greater attention to amelioration of forest soils.


Problems associated with nutrition and supplementary fertilisation of forest stands can be separated into two basic categories: the first one concerns nutrition of bare-rooted and balk-rooted seedlings in forest nurseries while the other involves reserves of nutrients and supplementary fertilisation of young stands. There are several types of fertilisers of different quality on our the market. When selecting suitable fertilisers, it is important to consider not only the content and ratios of essential nutrients but also the technical and personal aspects of their application under concrete conditions of forest stands. Today, not only finances but also methods of application belong to important limiting factors. When thinking about application of fertilisers in forest stands it is necessary to take into account some specific aspects of this activity, namely the need of a simple method of application and importance of long term effects of applied fertilisers. Tablets of slow-release fertilisers represent the product that meets these requirements.


There is a number of fertilisers of this type on the market at present. A gradual and slow release of nutrients results from different properties of these products and it is necessary to emphasise that the final results are rather different. The application of these fertilisers is important above all in young stands just after their establishment because they supply necessary nutrients during the most critical period, i. e. after planting and during the period of initial growth and development of the root system. In case of tree species this critical period can last as much as several years and is dependent above all on existing climatic conditions. It is quite clear that after planting it is not possible to assure such care and growing conditions for young trees as in the forest nursery.


Reserve, slow-release fertilisers enable to simplify the system of plant nutrition because the total dose of nutrients can be applied into the substrate at the beginning of growing season without any risk of a too high supply of nutrients. The period of fertiliser efficiency depends on the type and dose of fertiliser, properties of soil and climatic conditions. There are three basic groups of slow-release fertilisers:

  • biodegradable organic compounds;
  • slow-release fertilisers containing compounds with a low degree of solubility in water that are either hydrolysed or very slowly dissolved and
  • water-soluble fertilisers coated with compounds inhibiting their release.


Pellets of Osmocote® product line (manufacturer the Scotts® company) are probably the most frequent fertilisers of this type. They are used predominantly for nutrition of ornamental plants and are well-known in whole Europe. The release of nutrients from this fertiliser is dependent only on soil temperature. Its price, however, is a limiting factor because it ranges from 120 to 170 CZK per kg.


Slow-release fertilisers of SILVAMIX® series

Fertilisers of SILVAMIX® and SILVAGEN® series (manufacturer Ecolab Znojmo s.r.o.) belong to the groups of classical and special fertilisers developed for the needs of forest management. Their development and production were started in 1980´ on the base of an order of North Bohemian Forest Estate and they were used for the purpose of reforestation of areas destroyed by immissions. Both products are characterised by a slow release of nutrients and the rate of this release is dependent on soil humidity. The product is supplied in powdered, pelleted and/or briquetted form.


As defined by the manufacutrer, fertilisers of the SILVAMIX® series (SILVAMIX® MG, FORTE, A, J, W, R and SILVAGEN®) belong to the group of full and special fertilisers with a high content of nutrients that are gradually and slowly released (for a period of at least two years). These products are used for fertilisation and supplementary fertilisation of a wide spectrum of plant cultures. Nitrogen is supplied to plants mainly in the form of urea-aldehyde condensates (Ureaform) that show a different degree of water solubility in dependence on the length of polycondensate chain. This means that the fertiliser functions in soil as a slow source of nitrogen nutrition. There is no undesirable high concentration of nitrogen in soil solution at the beginning of the fertilisation and there are also no losses of this element from soil thereafter. A marked advantage of application of SILVAMIX® fertilisers represents the fact that they contain slowly soluble secondary potassium-magnesium phosphates that assure a very slow release of all essential nutrients, i. e. K, P and Mg.


A gradual release of nutrients represents the main difference between SILVAMIX® tablets and Preform pellets that were used in the Czechoslovak silviculture in years 1987 - 1992 (Nárovec 1989). Fertilisers of the Preform series contained quickly soluble components (urea, potassium sulphate and powdered superphosphate). It was demonstrated in lysimetric tests performed in the Research Institute of Forest Management (Research Station Opočno) with Preform tablets that nearly the total reserve of nitrogen was washed off within the period of only 2 months (and/or after the total sum of precipitation of 150 mm) and that about 70 % of potassium were released as well. Phosphorus, on the other hand, was not released from these tablets.


Table 1


Fertiliser Woody species Forest stand Number of tablets Season Note
Spring 2000 Autumn 2000
Height(cm) Root collar thickness(mm) Height(cm) Root collar thickness(mm)
SILVAMIX®MG Norway spruce 6 44.7 10.1 65.2 a 12.4 a Clearing - fertiliser applied at the moment of planting
4 45.5 10.1 63.3 a 12.6 a
2 47.1 10.2 61.2 a 12.8 a
0 50.3 10.1 61.7 a 11.4 a


Fertilisers of the SILVAMIX® series have a special feature: since 1983 these products had been developed and manufactured exclusively for the use in forests and in accordance with requirements of silvicultural practice. This fertiliser was designated above all for supplementary nutrition of young forest plantations on immission clear cuttings in the Ore mountains (Czech Republic) and its formula was specified by the former management of North Bohemian State Forests. The requirement on a gradual release of all nutrients was met through an optimisation of chemical composition of the fertiliser. In the years to follow, the fertiliser was widely applied in immission regions of the Czech Republic and Poland. We have started to test this fertiliser also in Slovakia in the year 2000.


The first results of experiments with application of SILVAMIX® MG fertiliser in Slovakia

When selecting the type of fertiliser it was decided to use SILVAMIX®MG either in the form of tablets (on new plantations and for cultures established in immission regions) or of a powder (sowings and bale-rooted seedlings in nurseries). Test of SILVAMIX®MG tablets took place in Forest Estates Námestovo and Beňuš. In both estates some stands were influenced by acid immissions.


Fertilisers were tested either directly during the spring planting or applied in older stands. To be able to carry out a more complex evaluation of effects of supplementary fertilisation on growth of forest cultures, not only different tree species but also different types of seedlings were used (in the Forest Estate Beňuš tests were carried with bale-rooted seedlings cultivated in Jiffy pots). Test were carried out with seedlings of Norway spruce, fir and beech. Results of these tests are presented in Tabs 2 and 3. These results are, however, only of preliminary character and for a complete and final evaluation of fertiliser application it will be necessary to carry out measurements also after the second growing season, i. e. in the period when the positive effects of the fertiliser should be the most marked. A positive effect of fertiliser application could be observed also in this stage of testing .


Table 2 Mean growth parameters of Norway spruce on a clear cutting in the locality of the Forest Estate Zákamenné before and after application of SILVAMIX® MG fertiliser


Fertiliser Woody speciesForest stand Number of tablets Season Note
Spring 2000 Autumn 2000
Height(cm) Root collar thickness(mm) Height(cm) Root collar thickness(mm)
SILVAMIX®MG Norway spruce 6 44.7 10.1 65.2 a 12.4 a Clearing - fertiliser applied at the moment of planting
4 45.5 10.1 63.3 a 12.6 a
2 47.1 10.2 61.2 a 12.8 a
0 50.3 10.1 61.7 a 11.4 a


Table 3 Effect of application of different doses of tablets of SILVAMIX® MG fertiliser on growth of one-year-old Jiffy seedlings of Norway spruce in the ea clear cutting in the experimental locality Jasienok (Forest Estate Beňuš)


Fertiliser Woody speciesForest stand Number of tablets Season Note
Spring 2000 Autumn 2000
Height(cm) Root collar thickness(mm) Height(cm) Root collar thickness(mm)
SILVAMIX®MG Norway spruceJiffy pots 6 8.4 2.9 16.0 a 3.9 a Autumn planting on a clearing (1999) fertiliser applied in the spring of 2000
4 8.8 2.6 16.6 a 3.8a
2 8.0 2.5 16.0 a 3.9 a
0 8.5 2.8 14.4 b 3.4 b


The powdered form of SILVAMIX®MG fertiliser was tested in the nursery on seedlings of beech, Norway spruce and fir. Positive effects of SILVAMIX®MG fertiliser on the growth of seedlings are illustrated in Tabs 4 and 5.


Table 4: Mean height of tops and root collar thickness of two-year-old seedlings of Norway spruce and fir after the application of SILVAMIX®MG fertiliser in the nursery Tanečník, Forest Estate Námestovo


Fertiliser Woody species Fertiliser dose
Season Note
Autumn 2000
Height (cm) Root collar thickness(mm)
Norway spruce 400 13.4 2.4 Nursed seedlings 1+1
Control 10.4 1.7
Fir 400 13.2 2.7 Nursed seedlings 2+1
Control 10.8 1.9


Table 5: Mean height of tops and root collar thickness of two-year-old seedlings of oak after the application of different doses of SILVAMIX®MG fertiliser in the nursery Stráž (Forest Research Institute Zvolen)


Fertiliser Woody species Fertiliser dose
Date of measurements Note
Spring 2000 Autumn 2000
Height(cm) Root collar thickness(mm) Height(cm) Root collar thickness(mm)
SILVAMIX®MG Oak 500 10.3 4.7 44.7 a 7.4 a Two-year-old oak seedlings
300 11.1 4.5 27.9 b 6.1 b
150 12.3 5.6 24.9 b 5.9 b
Control 12.8 5.0 17.5 c 4.9 b


Fertiliser application showed a marked effect especially on growth of beech seedlings. After the application of 500 g/m2 of powdered fertiliser the height increment was as much as 330 % and the thickness of root collar increased in a similar manner. Doses of 150 and 300g/m2 resulted in an increase by 100 % and 150 %, respectively. In controls, on the contrary, the annual height increment was only 36 %. When evaluating effects of SILVAMIX®MG fertiliser attention was paid not only to quantitative parameters of growth (i. e. to the height increment and the thickness of root collar) but also to the quality of planting stock (i. e. to the degree of maturity of the terminal shoot). Tops were able to mature even after the application of 500g/m2 and the quality of the root system of young seedlings was very good because the number of fine hairy roots was also high . Another advantage of application of SILVAMIX®MG in forest nurseries consists in the fact that its application is very simple and that it does not damage the leaf area of young plants. SILVAMIX®MG was applied to plants on 13 May, i. e. at the moment when the leaves of seedlings were fully developed. Although a great part of the applied powder remained on the surface of leaves and stems, no symptoms of the damage of assimilating organs were observed. As far as the problem of weed infestation was concerned, all beds were treated by the Roundup herbicide in the spring so that no weeds were observed during the whole growing season. In this context, however, it is necessary to emphasise that the application of SILVAMIX®MG fertiliser in the nursery may result in an intensive weed infestation and for that reason the treated beds must be sprayed with herbicides. In general, the application of SILVAMIX® fertilisers in powdered form seems to be efficient especially in small nurseries where it can be added directly into growing substrates (the substrate, however, must be well protected against weed infestation and the fertiliser itself should be uniformly distributed). Fertiliser application is very simple and does not damage the tops of seedlings. Very advantageous is also its long-term efficiency because, basing on results of the evaluation of growth and development of seedlings, it is sufficient to carry out only a single application on leaves in the next year.



Application of tablets of the SILVAMIX® fertiliser is simple and easily localisable. This means that it is possible to apply exact doses of nutrients to each plant and that the non-productive dressing outside the root system of young plants is really reduced to a minimum. Application of SILVAMIX® tablets saves time as well as labour and transport costs associated with the supplementary fertilisation of newly established stands later in the growing season or in the next year.


In this context it should be emphasised that any fertilisation of forest stands increases costs associated with production of young plant stock. This requires a complex analysis of the system of dressing and application of supplementary fertilisers only in those localities where this measure will produce the required effect (i. e. improvement of soil properties and shortening of cultivation period). For that reason it is necessary to carry out soil analysis prior to any fertiliser application and to define not only the dose of fertiliser but also the composition of supplied nutrients in a proper way. At present, the manufacturers are very flexible and can modify their products exactly according to requirements of their customers.


Zvolen (Slovakia), 2001