USE OF SLOW RELEASE TABLETTED FERTILIZERS SILVAMIX® WHEN GROWING FRUIT TREES IN COMMERCIAL NURSERIES (FINAL REPORT)

Good nursery products represent an indispensable predisposition for successful growing, early onset of fruit production, regular harvests and top quality of final products. Besides the traditional methods of production of young plants it is also possible to use containers which enable planting also in the course of growing season, i.e. not only in the spring or in the autumn. Although this method has a number of advantages, it is necessary to say that there also some factors or requirements which must be carefully observed and fulfilled. Losses of planted trees are very low, their root system is not damaged during transportation, plants continue to growth without any shock which could be caused by re-planting and the annual growth increments are sufficiently high.

When using this method of growing, it is necessary to use a suitable substrate, ensure adequate nutrition and fertilization, and provide sufficient and regular irrigation. This means that it is necessary to create optimum conditions for the development of root system of young plants. It is quite clear that containers have a special water regime and that the system of plant nutrition should be adapted to it. The lighter and more aerated substrates, the higher wash of nutrients due to top irrigation; for that reason it is necessary to use not only base but also regular supplementary fertilization. In case of bottom irrigation the wash-off of nutrients is not so intensive.

Low-soluble preparations are used for reserve fertilizing. Base fertilizing is usually used in case of spring planting. However, if the plants are placed into containers in the autumn, the fertilizer is applied on the soil surface next spring. However, higher doses of nutrients applied at the beginning of cultivation into containers inhibit the growth of plants. For that reason it is important to use slowly working fertilizers, especially those which are pressed into tablets. Among Czech products, pelleted and long-term soluble special feritlizers of the SILVAMIX® series represent a prospective product which is characterized by a gradual and slow release of supplied nutrients.

Experiments with the application of tabletted fertilizers in the field of production of young fruit trees in nurseries were established at our institute in 1993 and 1994. Seedlings in containers (growing pots) were placed in growing cages on the soil surface covered with a black plastic foil. In Experiments A and B, grafted apple trees and cuttings of black currant and an interspecific hybrid Josta, respectively, were used while Experiment C involved seedlings of rootstock species Prunus davidiana. The substrate for containers was prepared as a mixture of top soil and horticultural substrate B (1 : 1).

Established were the following variants (Experiments A, B, C): (1) Control; (2) SILVAMIX® A; (3) SILVAMIX® MG and (4) SILVAMIX® FORTE. Individual fruit species were planted into containers with 4.5 kg of the aforementioned substrate in the first decade of April.

In Experiment A, the following combinations were used: rootstock M9 and cultivars ‘Rubin’, ‘Melrose’, ‘Doris’ and ‘James Grieve’. Altogether 5 tablets (10 g each) were put into each growing pot at the moment of planting . During the growing season, the growth processes were maintained by means of regular irrigation, cultivation and weed control. To overwinter, the containers were placed together and covered by litter (leaves). In the course of the whole growing season, data about growth, i.e. about the length and numbers of annual shoots, were obtained in monthly intervals. In experiment C, parameters under study involved height of plants, weights of aboveground part and roots and damage by low temperatures. In Experiment B, percentages of Mg in leaves and annual shoots were calculated for both years under study.

In all experiments attention was paid to monitoring of growth parameters of plants placed in growing pots. In Experiment A, the following means of five measurings of the length of annual shoots were obtained:

15 June - 0.22 m; 16 July - 0.37 m; 15 August - 0.49 m; 16 September - 0.71 and 15 October - 0.77 m. In Variant 2 (SILVAMIX® A) , all measured values were higher than in control (Tab. 1). Similar results were obtained in Variant 3 (SILVAMIX® MG) while markedly higher increments were recorded in Variant 4, in which SILVAMIX® FORTE was used. The highest increments were observed in Variant 3 where, as compared with controls, this increase represented as much as 36.17% in 1993. In 1994, the highest increment was recorded in Variant 4 (28.12%). In 1993, the average number of annual shoots was markedly lower and the highest figures were recorded in Variant 3 (12.96%). In the following year, the increase in this variant was 64.58%; in Variants 2 and 4, the corresponding figures were 58.75% and 56.25 %, respectively. As far as the interspecific hybrid Josta was concerned, longer annual shoots than in controls were observed in all fertilized variants (Tab. 3). The best increments were recorded in 1993 in Variants 2 and 3, i.e. 44.0% and 42.0%, respectively. In 1994, the situation was nearly the same and the best results were recorded in Variants 2 and 4, i.e. 37.0% and 40.0%, respectively.

In the first year of growing, the average number of annual shoots was lower but in the second one a marked increase was recorded. The best results were obtained in Variant 3 (an increase by 26.0%), followed by Variant 2 (17.7%) and Variant 4 ( 10.4%).

Tabletted fertilizers showed a positive effect on both the height of plants and weights of tops and roots of P. davidiana rootstocks. The highest figures were measured in Variant 3 where the increase against controls was 20.2% (Tab. 4 ). Significant was also a reduced damage by low temperatures, especially in Variants 3 and 4. It is obvious that the nutritional status of plants affects the resistance of plants against low temperatures as well as their overwintering.

As far as the contents of Mg in annual shoots and leaves of black currant and Josta were concerned, higher values were observed in foliage of experimental plants in both experimental years. In the first year, these contents were higher than in the second one. In both experimental years, the highest contents of magnesium in annual shoots and leaves were recorded in Variants 3 and 4, respectively. A positive effect of tabletted fertilizers was observed above all in black currant and Josta; increased contents of this element were reported also by many other authors.

Table 1: Experiment A - Average annual increments in metres (1994)

Table 2 Experiment B - Growth data - black currant "Othello" cv.

Table 2 Experiment B - Growth data - black currant "Othello" cv. (continuation)

Table 3 Experiment B - Growth data - interspecific hybrid Josta.

Table 3 Experiment B - Growth data - interspecific hybrid Josta (continuation)

Table 4 Experiment C - Growth data and frost resistance of rootstocks P. davidiana (1993)

Table 5: Experiment B - Mg content in leaves and annual shoots (DM%) - black currant, josta