Submodule 1 2 planting stock production ebook by GEORGE DIAMANDIS

MODULE: Artificial forest regeneration SUBMODULE 1.2.: Production of container planting stock of forest tree species (Authors: Sarvaš, Takáčová, Tučeková)

1.2.1 Concept 1.2.1.1 Reasons for using container planting stock 1.2.1.2 History 1.2.1.3 Terminology 1.2.2 Facilities of forest nurseries producing container planting stock 1.2.2.1 Fully controlled production 1.2.2.2 Partly controlled production 1.2.2.3 Least controlled production 1.2.3 Greenhouses for container planting stock production 1.2.3.1 Temperature 1.2.3.1 Light 1.2.3.3 Air humidity 1.2.3.4 CO2 Concentration 1.2.4 Containers used in container planting stock production 1.2.5 Substrates used for container planting stock production 1.2.5.1 Properties of suitable substrate 1.2.6 Technology of container planting stock production 1.2.6.1 Sowing 1.2.6.2 Irrigation 1.2.6.3 Fertilisation 1.2.6.4 Storage in repositories 1.2.6.5 Frost hardiness 1.2.6.6 Deformations of root system

1.2.1. Concept 1.2.1.1

Reasons for using container planting stock in forest regeneration

Artificial reforestation is one of forestry activities with highest costs. It is therefore necessary to maximize potential of natural regeneration of forest stands with suitable genetic properties for a given site, because in addition to being the least financially demanding, it is the best tool to maintain an appropriate gene pool of forest tree species. On the other hand, it is clear that use of natural forest regeneration has its limits, mainly due to forest fires and calamities. Survival and faster growth of forest plantations can be increased by use of container planting stock. Advantages of this type of planting stock comparing with bare-rooted stock are obvious: • • • • • •

shorter time required for production of planting stock, higher effectiveness in using seeds, possibility to control conditions during production of planting stock, flexible production according to current demand, reduced number of planting stock needed for area being reforested, higher survival and faster growth of planted trees in reforested area

On the other hand, there are also disadvantages of containerized planting stock: • •

1.2.1.2

higher demands on technology equipment and staff, higher costs related to transportation.

History of using container planting stock

Use of container planting stock in larger extent started in the 30’s of the last century in the United States within the Great Plants Forestry Project. Containers used were made from paper (paper cells). Further development of container planting stock production is linked with use of plastic containers (especially in Canada). In Europe, usage of container planting stock was pioneered by Scandinavian countries in the late sixties. In addition to a numerous benefits of containerized planting stock, some significant disadvantages were also found. The disadvantages resulted mainly from deformation of root systems due to using inappropriate types of containers. These deformations occurred mainly in the first-generation containers (plain-wall containers), which caused the spiral growth of seedling roots in forest nurseries, which caused negative impact poor quality of pine plantations (LINDSTRÖM 1998) Problems with spiral roots were partially resolved in the late seventies through development use of containers with inner ribbing (LINDSTRÖM, HÅKANSSON 1995). Introduction of new types of packaging with vertical slots contributed to significant improvement in the quality of the root system of planting stock. These slots allow straight lateral root growth after planting, and thus "more natural root system" (RUNE 2003). 3

Attention was focused not only at traditional technologies (peat-cellulose containers, disconnectable containers-removed before planting) but also to the use of small-scale containers. These technologies come from the Scandinavian countries.

1.2.1.3

Terminology

Bare-rooted planting stock: Seedlings with generative or vegetative origin whose root system is not protected by terrain or other substrate when being replanted. Generally, bare-rooted planting stock is grown in natural soil on open-air plots.

Container "plug" planting stock: Seedlings with generative or vegetative origin whose root system is protected by growing substrate (roots plugged to substrate) also when being replanted. Generally, container planting stock is grown in artificial growth media (substrates) in controlled environment, where some parameters can be adjusted.

1.2.2 Facilities of forest nurseries producing container planting stock Main goal when producing container planting stock is to get high quality seedlings that meets customer requirements. Compared with production of bare-rooted planting stock, there is a possibility to use technologies controlling environmental conditions and thus creating more favourable conditions for growing the seedlings. According to degree of controlling individual environmental factors, we can classify following types of technologies: â&#x20AC;˘ â&#x20AC;˘ â&#x20AC;˘ 1.2.2.1

Fully controlled production Partly controlled production Least controlled production Fully controlled production

This type of technology allows to check and adjust all the factors at the optimal level and thus produce planting stock throughout the year. It is suitable for almost all types of climates and risk of damaging growing stock is very low. Its disadvantage is high investment and operating costs. These types of technologies use so called growing chambers or greenhouses. Main advantage of growth chambers over greenhouses is a possibility of full control of light conditions (duration, intensity, quality of light). Within greenhouses lightening is used to prevent too early dormancy (the more northern latitude the more important).

Growing chamber with full control of light and temperature

1.2.2.2

Partly controlled production

Under this type of cultivation there is a possibility to check only some selected environmental factors. Thus the production time is limited to the period spring - early autumn. 5

This type of production technology is associated mainly with use of plastic foil greenhouses and their similar modifications. 1.2.2.3

Least controlled production

This type of production requires the lowest investments and operating costs. The container planting stock is grown all the time in the open air. Length of the photoperiod can be controlled (adding artificial lighting), as well as water regime and nutrient availability. The strong disadvantage of this production technology is high risk of damage by abiotic factors (high temperature, downpour, hail, frost, etc.).

1.2.3 Greenhouses for container planting stock production Greenhouses for container stock production may be of various sizes as well as shapes but in general they can be classified according to the outer shape, material used for covering (plastic foil, glass) and whether standing alone or connected to each other. The main purpose a greenhouse is to capture maximum sunlight and simultaneously protect growing plants from unfavourable environmental condition thus creating optimal environmental factors for growing container planting stock. Selected shape of a greenhouse depends primarily on weather conditions. Designs with steeper slopes are more suitable in colder areas due to faster melting of snow. Generally, greenhouses standing alone are preferred nowadays, due to the higher flexibility. On the other hand, greenhouses that are connected - placed next to each other, occupy less area and have lower costs for air conditioning compared with enclosures standing alone. In practical designing and construction of greenhouses it is necessary to consider shape and orientation of the greenhouse, floor cover, supporting structures and choosing the appropriate coverage. When choosing place for a greenhouse, it is necessary to avoid some sites which may not be suitable (e.g. freeze-sites, danger of floods etc.) and consider direction of prevailing winds (to orient greenhouses so they are facing in the direction of prevailing winds). Selection of floor cover is a compromise between biological needs and financial possibilities. With regard to the possibility of eliminating harmful agents, the best solution is a solid concrete floor, which can eliminate the contamination of groundwater by chemical pest control products used in the nursery. On the other hand, this solution can be expensive, so if needed, paved (concrete) roads between rows can be the acceptable compromise. Unprotected soil on the floor is not recommended.

Plastic foil greenhouse

The purpose of supporting structure is to carry greenhouse cover with minimal shielding (allowing light to pass through the cover) and thermal loss, and simultaneously allow good access and manipulation in the greenhouse.

Currently, as a covering material to cover greenhouses for growing container planting stock, mainly plastic foil with following properties has been used: • • • • • • •

Low weight, High durability, Sufficient light transmittance Good insulating properties Solid and easy connecting of individual parts, Minimum water condensation, Affordable price

Because of thermal properties, PE and PVC are recommended. On the other hand, PA (polyamide) is not recommended.

Depending on technological equipment available in the nursery greenhouses following critical environmental factors is possible to control:

1.2.3.1

Temperature

Temperature has a direct effect on the metabolism of a plant, because the level of biochemical reactions increase with temperature up to a level where enzymes are damaged. Effect of temperature on growth of individual plant parts is very different. Therefore it is important to focus attention not only on air temperature, but also on temperature of substrate around the root system. The optimum temperature also depends on the growth phase. The optimum air temperature is between 15 and 25° C. At the time of germination, air temperature may not be higher than 25° C and during the later growth stages may not be higher than 35° C. The optimum temperature of the root system is 17-25° C. Table bellow presents impact of different temperature regimes on germination of four pine species. Effect of different temperature on germination of selected pine species (seeds were not stratified) (DUNLAP, BARNETT 1982) Germination rate (%) Species 24 °C (18 hrs.) + 24 °C 35 °C 35 °C (6 hrs.) Pinus 79 61 12 palustris Pinus 84 83 71 elliottii 8

Pinus taeda Pinus echinata

88 89

78 76

Achieving and maintaining optimum temperature directly depends on technological equipment of the greenhouse. Under fully controlled conditions, it is possible to regulate the temperature in both directions (additional heating / cooling). Under partially controlled conditions, the focus is primarily on lowering the temperature by shielding or ventilation . Ventilation is particularly important in summer, when large amount of light energy is accumulated, what can have a negative effect on the growth of seedlings. The easiest way to reduce the temperature is to open the cover (gates and openings on the top). This method of ventilation is based on the principle that the lighter warm air exits the housing through the opening and is being replaced by heavier cold air. This method of ventilation is influenced by four factors: shape of the greenhouse construction, placement of ventilation holes, wind speed and its direction, and difference between the outside and inside temperature.

Ventilation through roof openings. (Photo: Sarvaš)

In general, this ventilation method is more suitable for higher greenhouses. In case of wind speed over 10 km per hour, the openings on the leeward side should be open on its maximum and vice versa vents on the windward side of the roof should remain closed. This will ensure 9

faster air exchange. Of course, this type of ventilation is effective only if the outside air temperature do not exceeds 38째 C (Land et al. 1990). Use of fans is more effective way of ventilation. On the other hand, the system is more expensive.

Lowering the temperature in summer can also be supported through shielding. On the other hand, this method reduces amount of solar radiation, which can have a negative impact on growth, mainly on growth of root system (BARNETT 1989). In addition to reducing the temperature in summer, heating may be necessary to ensure optimum temperature in the spring, especially for early sowings in areas with colder climate. Heating is very costly (operating costs) and the deciding factor is choosing the optimal energy conductor.

1.2.3.2

Light

The light is a complex factor that affects growth of planting stock in forest nurseries. Three main properties of light affect plant growth: intensity, duration and quality. To ensure optimal plant growth, the light source must provide sufficient energy input for photosynthesis. Optimal light intensity is 23-35 klx. Duration of light is directly related to the day length. The quality of light is expressed by its wavelength. Light with wavelength of 440620 nm have the most significant impact on growth. Extension of photoperiod length (duration of light during a day) can help, mainly in higher latitudes. E.g. a positive impact of photoperiod extension on growth of aboveground part of spruce container planting stock was recorded in early spring sowings was recorded.

Sodium spotlight lamps (400 W, 5000 lx). (Photo: Sarvaš)

Natural photoperiod length. (Photo: Takáčová)

24 hour photoperiod length. (Photo: Takáčová)

1.2.3.3

Air humidity

Relative air humidity and substrate moisture have direct impact on the growth when growing container planting stock. Relative air humidity below 50% reduces photosynthesis. The optimal level of relative air humidity depends on a growth phase. The optimum relative air humidity for the particular growth phases (Land et al. 1992) Relative air humidity (%) Growth phase Optimum Span Germination 80 60 – 90 Fast growth 60 50 – 80 Hardening Open air environment

1.2.3.4

CO2 Concentration

CO2 concentration in the air has decisive influence on the extent of photosynthesis. Natural CO2 concentration level is about 350 ppm. However, the optimal level of CO2 concentration with respect to the plant growth is higher. CO2 concentration can be increased by ventilation, or by direct supply. Table 20: Effect of different CO2 concentration levels on plants and the human body

Effect Plant Stopping the growth Growth reduction Natural concentration Enhanced growth Small positive effect Negative effect Human body Tolerable upper level Headache, tiredness Loss of consciousness, Dead

concentration (ppm) CO2

< 100 100 – 350 350 300 – 1 000 1 000 – 2 500 < 2 500 5 000 > 5 000 > 80 000

1.2.4 Containers used in container planting stock production Container parameters (mainly volume and height) directly affect growth of the root system of young plants. Survival and subsequent growth after planting is directly related to the growth of new roots and their overgrowth into surrounding soil. Root system parameters are reflected in the growth of aboveground parts and these factors should be taken into account when assessing individual characteristics of packaging. Container parameters (mainly volume and height) directly affect the growth of the root system of young plants. Survival and subsequent growth after planting is directly related to the growth of new roots and their penetration into the surrounding soil. Root system parameters are reflected in the growth of aboveground parts and these factors should be taken into account when assessing parameters of containers. Table: Effect of varying volume of containers on morphological parameters of Pinus contorta (Dougl.) - 20 weeks after sowing (ENDEAN, CARLSON 1975) Biomass â&#x20AC;&#x201C; dry matter Container Ratio Stem (mg) volume height stem/root (cm ) (mm) 3

Roots

Stem

Total length

150

246

1,6

222

319

541

1,4

335

389

724

1,2

498

722

1 220

1,5

131

638

936

1 573

1,5

262

790

1 265

2 055

1,6

524

897

1 544

2 440

1,8

Volume is the main container parameter. Genetally, the larger container, the larger plant can be grown. On the other hand, larger volumes of containers have a negative impact on economic aspects: â&#x20AC;˘ â&#x20AC;˘

Larger containers mean less production area Handling and transportation of nursery stock in larger containers is more difficult

When designing the container volume, it is necessary to take into account several parameters, not only in production in forest nurseries but also the environmental conditions at the planting site. In Slovakia, containers with volume of 150 to 250 cubic centimetres are used for production of one year old seedlings, and for older seedlings the container volume reaches up to 350 - 400 cm3. Above-ground height of planting stock to be produced is the main parameter which derives the container size. Similarly, in Finland, cultivation density is the main indicator of defining allowed height of above-ground part. (number of containers/m2 ): 14

Table: Allowed maximum height of above ground parts of container spruce seedlings, depending on the cultivation density (RIKALA 2000) Cultivation Maximum density (container/m ) allowed height (cm) < 300 40 300 – 399 35 400 – 499 30 500 – 599 26 600 – 799 23 800 – 999 20 1 000 – 1 299 17 1 300 – 1 600 16 2

Table: Recommended container size for growing planting stock. Container size Aboveground Minimum height (cm) allowed (cm) Tree species container height (cm) Upper diameter up to 35

Beech, oaks, maples, ash trees

Scotch pine

36 – 50

do 35

36 – 50

51 – 80

81 – 120

10 – 14

15 – 25

26 – 35

36 – 50

51 – 80

81 – 120

up to 35 36 – 50

Silver fir

51 – 80

81 – 120

26 – 50

do 50

51 – 80

81 – 120

36 – 50

51 – 80

81 – 120

up to 25

European larch

up to 35

Douglas fir

Norway spruce

Container height

36 – 50

51 – 80

81 – 120

Depending on material, containers can be divided into following groups • •

Rigid containers (containers not allowing growth roots though them) Soft containers (containers allow roots to penetrate through it) - not necessary to remove them before planting 16

Rigid containers are mostly connected together to the trays. Individual rigid containers are used rarely, especially in the cultivation of larger plants.

Rigid containers (beech seedlings 5 weeks after sowing). (Photo: Takáčová)

Soft containers (beech seedlings 3 weeks after sowing in Jiffy 7 Forestry containers on the left, and spruce seedlings in peat-cellulose containers on the right). (Photo: Takáčová)

1.2.5 Substrates used for container planting stock production Substrates are classified according to the organic content as follows: • •

organic substrates ( content of combustible matter more than15 % ) mineral (combustible materials below 15 %).

Suitable substrate should meet the following criteria: • •

• •

Ensuring sufficient water availability - plants grown in containers , compared to plants cultivated in the open area have limited growth area and this factor has a direct impact on limited water availability Ensure sufficient exchange of O2 and CO2 in the root system - by aerobic respiration produces carbon dioxide, which can accumulate in substrate to toxic levels and therefore the substrate must have sufficient porosity to provide sufficient exchange capacity Ensuring sufficient intake of nutrients - plants receive the majority of nutrients ( in the form of cations ) from water solution and therefore it is necessary that the substrate has high cation exchange capacity Ensure sufficient mechanical stability and desired plant growth - substrate must be compact enough to ensure stability of the plant.

1.2.5.1

Properties of suitable substrate

Currently, peat substrates are most commonly used for the production of container planting stock. All types of peat can be used for production of substrates (highland peat, moor peat etc.). Suitable substrate for growing container planting material must meet a number of criteria that can be divided into two basic groups: •

Criteria that influence the growth of plants:  Suitable pH - substrate pH depends on proportional composition of various components of the substrate and their pH and cultivation methods (mainly irrigation and fertilization). pH affects nutrient intake, occurrence and number of microorganisms in the substrate including fungal pathogens (Landis et al. 1990). Recommended value of pH/H2O is 5.0 to 6.0 for hardwoods and 4.5 to 5.5 for softwoods.  High cation exchange capacity – this is the most important characteristic affecting intake of nutrients. In the form of cations, plants absorb nutrients - calcium (Ca2+), magnesium (Mg2+) , potassium (K+) , nitrogen (NH4+) as well as microelements ( iron , manganese , zinc , copper , etc. ) . These nutrients are embedded in a substrate in places with high cation exchange capacity, and taken by plant through the root system  Low internal nutrient levels - at the time of germination, plants do not require nutrients for their growth. Conversely, high levels of nutrients during germination, especially nitrogen, may promote the spread of fungal pathogens.  Porosity - suitable physical structure of the substrate provides sufficient gas exchange in the root system, which has a direct impact on intake of water and nutrients. Recommended values for the porosity of the substrate vary significantly. 18



•

They range from 50 to 80 % (HANDRECK, BLACK 1984 HAVIS, HAMILTON 1976). Required purity - for successful production of planting stock, the substrates may not contain weed seeds and various kinds of pathogens.

Criteria affecting production technology  High degree of uniformity and stability - it is important that the chemical and physical properties of the substrate do not differ among deliveries and guarantee the desired outcome for the same growing techniques  Low density - defined as kg/m3. Density depends on chemical composition and physical structure of the individual components in the substrate. Its value is provided for absolutely dry substrate. However, density is of great importance even in wet state, as it affect handling and transport of the planting stock  Durability and easy storage  Easy to put into containers  Ability to be re-irrigated  Price

There is no universal substrate for growing planting stock. It is recommended to use highquality though more expensive substrate produced by a certified supplier rather than cheaper but less quality substrate or prepare substrate in forest nursery. Higher input costs bring economic effect through the quality of planting stock produced.

1.2.6 Technology of container planting stock production 1.2.6.1

Sowing

Seeds quality is a basic precondition for successful production of container planting stock. The best solution is to place one seed into the cell (container). When using seeds of worse quality, 2-3 seeds should be placed into each cell. However, this increases personal costs - snipping young seedlings if several seeds germinated in one cell. An important feature of seed quality is so called germination energy, which is essential for growth homogeneity. Larger seeds (beechmast, acorns) are better to sown when sprouted - sprouts down. A seed should be placed at the middle of cell. It is necessary to compact the substrate before sowing it is recommended to place more substrate - about 10 % more than capacity of the container. An important factor of protecting the sown seeds (especially small seeds) is to cover them by thin layer of substrate. Thickness of this layer should be up to 0.5 cm for small seeds, and up to 1.0 cm for larger ones. When sowing small seeds (e.g. spruce or pine) in higher number of trays, sowing lines can be efficient to perform placing substrate into trays and flattening it, sowing itself, and covering seeds by soil. Time of sowing depends on temperature and photoperiod length. The optimum temperature is 15-20°C. In early spring sowings in more northern latitudes, it is necessary to provide additional light by using lightening (16 hrs. day-length) to prevent risk of growth arrest.

Germinated spruce – 12 days after sowing (photo: Takáčová)

Germinating beech – 15 days after sowing (photo: Takáčová)

1.2.6.2

Irrigation

Water is a limiting factor for plant growth. Almost every physiological process in a plant is affected by water. Several factors must be taken into account when designing an irrigation scheme for container planting stock production. Size of containers and their upper diameter are ones of the most important factors. As containers used for growing planting stock have a small diameter and low volume, it is difficult to ensure uniformity of irrigation dose especially in hardwoods. Loss of water is due to evaporation (directly from the substrate) and plant transpiration. Both of these are affected by high temperature, low air humidity and air movement. Water used for irrigation must not be chemically contamined or with mechanical impurities - the danger of clogging of irrigation nozzles. Irrigation intensity should not exceed 3 mm/h.

Stable upper irrigation. (Photo: Sarvaš) High constant humidity as well as avoiding substrate waterlogging must be ensured especially when producing container planting stock by vegetative reproduction. Therefore, irrigation equipment used works on the principle of fogging when water is sprayed under high pressure through a nozzle of small diameter. Droplet size in this irrigation system is between 5 and 50 μm.

Fogging equipment with compressor and control unit. (Photo: Sarvaš)

Need for irrigation must be monitored to set proper intensity of irrigation. There are several methods to monitor a need for irrigation - from simple - visual observation to much more exact e.g. detection of water potential of plants with a pressure chamber). An acceptable and reliable compromise, which is fast and does not require expensive equipment is to weigh the container trays. Principle of this method is based on the fact that overall weight trays can change mostly depending on water content in the substrate. It is necessary to weigh the trays more times, until the optimal weight of trays is set to control irrigation needs. Table: Weights depending on the growth phase of coniferous planting stock (LANDIS et al. 1989) Irrigation weight * (% out Growth phase of total weight**) Germination 90 Fast growth 80 Hardening 65 – 70 After bud creation 75 Storing 80 – 85 * weight when irrigation is needed, ** weight during maximum water capacity of the substrate Irrigation (beside water supply for plants), can also play role of „adapting“ to external environmental conditions. In summer, it means mostly temperature reduction (freshening sprays). On the contrary, in autumn and spring seasons in repositories - as protection against early or late frosts, respectively. Of course, these measures are effective only to a certain extent, and especially in anti-freeze spraying depend on air movement velocity. Table: Irrigation dose depending on temperature and air movement velocity (HANSEN et al. 1979) Temperature Irrigation dose (mm/h) (°C) 0 – 0,05 1,0 – 2,5 3,0 – 5,0 km/h km/h km/h -3 2,5 2,5 2,5 -4 2,5 3,5 5,5 -5 3,0 5,0 — -6 3,5 6,5 — -8 5,0 — —

1.2.6.3

Fertilisation

The goal of fertilization is to deliver nutrients for plants in required amount, form and proportion. Fertilization is mainly concentrated on the delivery of six basic elements (N, P, K, Ca, Mg, S) and partially to seven microelements (Fe, Mn, Zn, Cu, B, C, Mo).

When growing container planting stock, there are several factors to be considered when designing fertilization specific for particular conditions: •

Substrate

It is necessary to take into account the content of nutrients in the substrate and based on this specifically adapt fertilization practices. •

Container size

Containers used in planting stock production have a relatively small volume (up to 500 cm3). Therefore, especially in phase of fast growth, concentration and ratio of nutrients are rapidly changing. Therefore, it is important to regularly check and then supply the nutrients. •

Relation between pH and nutrients

pH value of the substrate has a direct impact on the ability of nutrients intake. At extreme pH values (in both directions), mechanism of a nutrient intake is malfunctioned. The recommended pH for coniferous and deciduous tree species are listed in chapter 1.2.5.1 Properties of suitable substrate •

Water content in substrate

Fertilization is directly dependent on water content in the substrate - low water content dramatically reduces efficiency of fertilization. •

Content of salts

Soluble salts may have a negative effect on intake of some nutrients. •

Determining the appropriate fertilization

When adjusting the fertilization regime, it is necessary to determine concentration of nutrients, ratio between nutrients and take into account the growth phase. Low concentration of nutrients is ineffective; however, high concentration may directly damage planting stock. Several units of concentrations can be used in determining the appropriate fertilisation, but the most common ones are the unit of weight - mg/l (milligrams per litre) and proportional unit - ppm (part per million). For determining the concentration of nutrients in the water the conversion between units is 1:1. Several fertilization methods are based on the concentration of nitrogen as the main nutrient. There is number of recommendations for concentration of nutrients depending on the growth phase. Table: Recommended values of nitrogen fertilization at different growth stages Applied dose (ppm) Author Initial Fast growth growth Hardening phase phase 24

MULLIN , HALLETT (1983) CARLSON (1983) pine spruce Douglas fir TINUS, MCDONALD (1979) INGESTAD (1979) Scotch pine spruce MORRISON (1974) BRIX, van den DRIESSCHE (1974)

100

225 112 62

229 112 100

45 45 62

—

223

— —

20 – 50 60 – 100

— —

—

50 – 300

—

28 – 300

—

Balanced ratio between nutrients is important because an excess of one nutrient can affect intake and utilization of other nutrients. Table: Target nutrient content for fertilization by liquid fertilizer (Landis et al. 1989)

Nutrient application Generally, there are two main methods of nutrient application:

1. Application of a fertilizer directly to substrate. 2. Application of liquid fertilizer through irrigation. Direct application of a fertilizer to substrate has following advantages: • •

No need for special application equipment Low costs for mixing and application compared with liquid fertilizers

Its main disadvantages are as follows: • •

No possibility to continuously control concentration and balance between nutrients in substrate Necessity to ensure proper mixing of fertilizers in the substrate

Improper mixing of fertilizer with substrate can cause problems mainly when small containers are used – risk of uneven nutrient concentration and thus uneven growth. Application of liquid fertilizers has following advantages: • • •

Exact control of dosing particular nutrients, Possibility for flexible changes in fertilisation regimes, Low risk of overdosing the fertilizer.

Disadvantages of liquid fertilizer applications results from higher costs mainly related to the need for a liquid fertilizer dispenser and appropriate irrigation system

Preparation of liquid fertilizer Preparation of liquid fertilizer should be based on required target concentration of fertilizer to be applied. Other parameters are the chemical composition of water and fertilizer - water mixing ratio. In setting appropriate dose of the fertilizer, it is necessary to bear in mind different ways of declaring contents of main nutrients. Nitrogen is referred to as total, phosphorus as content of P2O5 and potassium as content of K2O. Table: Conversion of nutrients (Landis et al. 1989) Form to be Coefficient Conversion to converted (multiplication) P 0,4364 PO P 2,291 PO K 0,8301 KO K 1,205 KO 2

Monitoring of fertilisation Regular monitoring of fertilization is necessary for successful growing of container planting stock. The monitoring can be done by measuring of different factors. The basic characteristics that reflect supply of nutrients are electrical conductivity of solution and nutrient content in plant tissues. Measuring electrical conductivity determines salt content and it is a quick method of measuring nutrient content. Detection of nutrient content in plant tissues is the most accurate but costly method, and results are not available immediately. Table: Recommended values of nutrient content (%) in leaves (in dry weight) (Landis et al. 1989) Recommended content (%) Nutrient N 1,40 – 2,20 P 0,20 – 0,40 K 0,40 – 1,50 Ca 0,20 – 0,40 Mg 0,10 – 0,30 S 0,20 – 0,30 The monitoring itself should be conducted in following stages: • • •

•

1.2.6.4

Irrigation water - you need to determine values of electrical conductivity and pH of the water and take these characteristics into account when setting appropriate fertilization; and check these parameters in regular intervals, Concentrated liquid fertilizer - prepared liquid fertilizer, which is later diluted with irrigation water by dispensing pump. The difference between electrical conductivity of prepared fertilizer and directly applied fertilizer should not be more than 10% Applied fertilizer (through irrigation) - this is the most important part of the monitoring as it directly comes into contact with aboveground parts of a plant. Electrical conductivity and pH values should be monitored. Measurement should be carried out directly at the exit of the nozzle. Conductivity values are approximately the sum of natural salt content in water and salts added through fertilization. The pH should vary around 5.5. Leachate (extract) from a container - it's the final test of fertilization. Samples for measurement should be taken from several containers.

Storage in repositories

When container planting stock reaches required morphological parameters (height of aboveground parts, root collar diameter), it is transported to a repository. Storage area should be paved and free of weeds. Area of plastic foil greenhouse (after removing the foil) can also be used as a repository. In such case, transport of planting stock is not necessary.

Greenhouse used as a repository after removing the plastic foil from greenhouse construction (protection net against direct sunshine). (Photo: Sarvaš) Ensuring adequate irrigation is a prerequisite for safe storing. In order to avoid deformation of root systems, it is is necessary to ensure air space (air pad) under each tray (as well as in growing greenhouses). The air must flow between plants, although excessive airflow causes excessive drying of substrate and roots. Bearing surface may not consist of horizontal surfaces (such as crates, which are not suitable because of horizontal surfaces).

Suitable design of trays and bearing construction without horizontal surfaces ensuring cutting roots by air (avoiding roots deformations). (Photo: Takáčová)

1.2.6.5

Frost hardiness

Container planting stock is grown in an intensive way. The aim of this production is to obtain seedlings suitable for planting, possibly in the shortest period of time. One of the crucial parameters affecting successful production of planting stock in colder climates is its resistance to withstand low temperatures (frost resistance ). Due to intensive cultivation method there may be a risk of inadequate maturation (lignifications) of aboveground parts, and thus its damage by early autumn frosts or late spring frosts.

Equally important is the risk of frost damage to the root system of seedlings stored in a repository. Therefore, attention should be paid to determination of resistance potential against frost. On the basis of information on actual resistance to frost, some measures increasing frost resistance should be carried out. Shortening photoperiod is the most important factor affecting formation of terminal buds in coniferous planting material and to stop growth of stems, which can have a significant effect on increasing resistance to frost. Beside the length of photoperiod, low temperature is the most important factor affecting frost hardiness of conifers (RYYPPÖ 1998). Low temperature (typically below 5°C) significantly affects the physiological processes, which are directly involved in increasing resistance to frost (Sarvaš 2003). Gradual change of temperature (from higher to lower temperatures) causes greater resistance to frost rather than direct change in temperature conditions (Timm 1978 COLOMBO 1994). Low temperature is of great importance also for hardening the root system as opposed to the stem, for which the decisive factor is the photoperiod length. In addition to measures that are carried out to mitigate the weather conditions, some products are widely used to accelerate maturation (lignifications) of aboveground parts. In practice, fertilizers low in N (FLØISTAD, Kohmann 2004) and high P or K (Edwards 1989) are commonly used before the end of the growing season. Sarvaš (2004) found a positive impact of “Cukrovital K 400” application (liquid concentrate of organically bound potassium) on the growth of new roots of container oak planting stock after frost test conducted in autumn season. Table: Growth of new roots 49 days after frost test – application of organically bound potassium (SARVAŠ 2004) Growth of new roots* Growth of new roots* Variant

Application of Control plots “Cukrovital K 400” (no application) + 5 °C 4,2 3,0 -5 °C 4,0 3,0 -10 °C 3,8 2,4 -15 °C 2,6 1,2 *Growth of new roots: 0 – no growth; 1 – some new roots, shorter than 1cm; 2 – 1–3 new roots longer than 1 cm, 3 – 4–10 new roots longer than 1 cm, 4 – 11–30 new roots longer than 1 cm, 5 – more than 30 new roots longer than 1 cm Beside the risk of frost damage by early autumn frosts, another critical point is storing of planting stock during winter period. Trays placed on open areas do not provide sufficient protection against low temperatures during winter in regions with cold climate. The best approach is to perform reforestation (planting) during autumn and avoid storing the planting stock during winter in repository.

1.2.6.6

Deformations of root system

When growing container planting stock of forest trees, growth and development of the root system is different compared to growth of young trees from natural regeneration. Using improper packaging as well as incorrect production and planting procedures cause roots deformation and subsequent reduced stability of forest stands in future. Several studies from Nordic countries have confirmed an assumption that the root distortions caused reduced mechanical stability of forest stands, reduction in growth, and trees with deformed root system were more affected by fungal infections. MAUER et al. (2006) reported the following types of root system deformations: • • • • •

Flattening into vertical plane Flattening into horizontal plane One-sided “flag” formations U-shaped and J-shaped deformations Entanglement of roots in container space

U-shaped and deformations (Photo: Tučeková)

Entanglement of roots in container space (Photo: Tučeková) Measures to eliminate the occurrence of deformations of the root system:

• • • • •

Placing trays on an air pad (air layer) during all cultivation time Shorten time of growing the seedlings in containers - possibility to replant stock into larger containers Adding ribs on the inner side of containers prevents turning roots around inner side of container (spiral growth) Improving shape of containers – using containers with corners (to guide root growth downwards) instead of round containers (causing spiral growth) Application of inhibiting chemical substances at the inside of containers.