Containerised forest nurseries

Containerised forest nurseries Planning and operating a commercial plantation forest seedling nursery

Warrick Nelson

Also by Warrick Nelson Propagating plantation trees from cuttings in containers

© 2012 Warrick Nelson, all rights reserved Title: Containerised forest nurseries Publisher: 888 Management Ltd Christchurch New Zealand Available through www.lulu.com

Layout using Writer (openoffice.org) in Gentium Book Basic typeface (scripts.sil.org/Gentium)

Table of Contents

Introduction.....................................................................................1 Why containerised stock?...........................................................................1 Designing from scratch................................................................................2 Acknowledgements................................................................................2

1. Containers - evolving ideas.........................................................4 Cells shape root systems..............................................................................5 Root-pruning features.............................................................................6 Air-pruning.............................................................................................7 Chemical pruning...................................................................................8 Other pruning systems..........................................................................10 Benefits of root-pruning............................................................................10 Predictable container shaping with no pruning....................................11 Cell size, shape and density.......................................................................14 Cell size................................................................................................14 Cell shape.............................................................................................15 Density..................................................................................................15 Common specifications........................................................................17 Configuration, manufacture and handling features..............................17 Configuration........................................................................................17 Manufacture..........................................................................................18 Disposal................................................................................................20 Handling features.................................................................................21

2. Growing medium - filling the space.........................................23 Chemical.......................................................................................................23 pH.........................................................................................................23 Cation exchange capacity.....................................................................25 Buffering capacity................................................................................26 Electrical conductivity..........................................................................26 Nutrients...............................................................................................27 Contaminants........................................................................................28 Physical........................................................................................................28 Bulk density..........................................................................................29 Porosity.................................................................................................30 Water holding capacity.........................................................................32 Air filled porosity.................................................................................34 Particle size and shape..........................................................................34 Drainage...............................................................................................36 Shrinkage..............................................................................................37 Biological factors during storage.............................................................38 Components.................................................................................................39 Mixing and handling............................................................................39 Additives...............................................................................................41

Management factors..................................................................................42

3. Watering - preventing parching..............................................44 Planning an installation........................................................................44 Capacity - storage, flow..............................................................................44 Maximum daily requirement................................................................45 Average daily requirement...................................................................45 Maximum flow rate..............................................................................45 Physical installation..............................................................................46 Application methods..................................................................................48 Hand.....................................................................................................48 Fixed sprinkler......................................................................................49 Travelling irrigation boom...................................................................50 Capillary and ebb and flow systems.....................................................51 Automation...........................................................................................52 Quality..........................................................................................................53 Chemical...............................................................................................53 pH.........................................................................................................54 Conductivity.........................................................................................54 Other chemical components.................................................................56 Pathogens and weeds............................................................................57 Temperature..........................................................................................59 Water sources..............................................................................................59 Rainwater..............................................................................................59 Domestic treated supply.......................................................................60 Bore holes and springs.........................................................................60 Recycling and treatment.......................................................................60 When and how much..................................................................................61 Too often, too little...............................................................................61 Too much, too fast................................................................................61 After severe drying...............................................................................63 Testing when to water...........................................................................63 Edge and patch effects..........................................................................65 Measuring uniformity of watering.......................................................68 Drains and waste water..............................................................................68

4. Nutrition - feeding the baby.....................................................70 Nutrients......................................................................................................71 Application..................................................................................................72 Solids....................................................................................................72 Liquids..................................................................................................73 Organic.................................................................................................75 Monitoring and management...................................................................76 Fertigation strategy...............................................................................78

5. Hygiene - keeping clean............................................................82

Weeds...........................................................................................................82 Other plants in the nursery...................................................................83 Fungi.............................................................................................................84 Damping off..........................................................................................84 Mildews and blights.............................................................................85 Root diseases........................................................................................85 Mycorrhizae..........................................................................................86 Pests..............................................................................................................87 Algae.............................................................................................................88 Chemical contamination...........................................................................89 Accidental.............................................................................................89 Deliberate.............................................................................................90 Spray drift.............................................................................................91 Tray cleaning...............................................................................................91

6. Climate - feel the difference.....................................................93 Greenhouse climate control......................................................................93 Seed germination........................................................................................94

7. General and practical tips - let's get on with it......................96 Size specifications.......................................................................................96 Hardening of plants....................................................................................96 Height control.............................................................................................99 Grading, packing and transport.............................................................100 Planting......................................................................................................101 Plug propagation......................................................................................101 Logistics.....................................................................................................102 Costing........................................................................................................104 Scheduling.................................................................................................106 Risk analysis..............................................................................................106 Calibrating pH and conductivity meters...............................................107 Conductivity units of measure................................................................107 Acronyms...................................................................................................108

http://www.lulu.com/spotlight/warricknelson Evaluation version

Introduction

1

Introduction I began planning this manual during the 1980s plantation forestry investment boom. The 1990s investment boom reinforced my view that forest nursery technology was not being well passed on from one investment cycle to the next. A noticeable change between these two investment booms was the recognition that forest nursery management was a career path distinct from plantation forestry itself. A number of forest nursery manuals have since been published, but I felt that my approach was more directed to nonacademic needs, even though many forestry companies manage their nurseries through their research divisions. Further, there are many privately owned and operated nurseries commonly entering the industry without forestry training. Good quality planting stock is one of the key foundations for the success of the plantation investment. I have attempted to keep this manual as practical as possible, emphasising the principle to be understood and explaining it with a range of altern atives to achieve good practice. Choice of materials in the nursery can sometimes reduce the skill levels required to produce a good plant, for example using an excellent growing medium makes watering practices very much simpler than using a poorer quality product. But a fully standardised growing process cannot be described, nor can a set of procedures replace the skill of a good manager and staff. References for more detailed reading on topics have only been included in a few very specific cases. This manual is intended to be for practical use and not an academic resource.

Why containerised stock? Speed and quality of planting are probably the most important aspects for choosing containerised planting stock. Many others might come into play too, such as being able to plant at otherwise non-standard times, e.g. where actively-growing stock is planted in warmer months, or to overcome issues such as methyl bromide to treat nursery beds against root pathogens, or the cost of land and water (container nurseries are typically far more efficient

2

Introduction

in use of both of these per seedling sent for planting). Scale of production and opportunities for mechanisation are available for containerised nurseries, for example producing 25-100 million plants is quite feasible in a con tainerised nursery management structure with a single manager.

Designing from scratch Planning a new nursery is an exciting process. It is at this early stage that many aspects of the success of a tree plantation can be influenced. In par ticular, how the choice of the container system will impact on subsequent tree growth. This is the single most important aspect where a decision made in the nursery impacts on plantation growth. There are many other nursery decisions that will affect a batch of seedlings, for example produ cing sufficiently hardened plants, or nutritional aspects known to have impacts later in plantation life. However, choice of containers fixes so many aspects, from root-pruning to plant density, that this choice must not be made lightly, or for simple short-term economic aspects affecting only the nursery stage. Planning a nursery layout is akin to a production flow process. Movement of materials within the nursery, placement of activities, and the decision whether to move plants to an activity, or for the activity to occur where the plants are positioned, are key decisions driving effective use of resources. There can be no single prescribed method, and new technologies and efficiencies are constantly being developed. Visit many nurseries and “steal with your eyes” is a good means of introducing improvements in your own nursery. Join a forest nursery association and participate fully in dis cussions and visits to nurseries. Acknowledgements I have had the pleasure of knowing and working with many nursery managers and researchers. These have included forestry, vegetable and general propagation (ornamental) nursery systems. In particular, I must mention the enormous help and guidance I have received from members of the Seedling Growers Association of Southern Africa, the New Zealand and Australian Forest Nursery Associations, International Plant Propagators' Society, In-

Introduction

3

stitute for Commercial Forestry Research, Pietermaritzburg, South Africa, New Zealand Forest Research Institute (Scion), and the many nursery managers in Africa, SE Asia, Australasia and South America who answered my many questions or who were so generous with their time in arranging nursery tours. [email protected]

4

1. Containers - evolving ideas

1. Containers - evolving ideas The concept of the ideal container for containerised tree seedling propagation has changed dramatically over the years. Lateral root-pruning and shorter depth of the cells are the two most important areas now coming into general practice. "What is the ideal size of container?" is a common question put to forest nursery researchers. While an absolute answer is not possible, we can now go a lot further towards suggesting a range of excellent options. Most of these ideas have been developing over the last thirty years, reflecting the long lead time between the idea and the confidence to introduce it after a suitable trial period. Containers linked together as cells in a growing tray fix the space available for growth and affect the root form. Cell volume affects nutrient and water availability as well as light penetration between plants. While occasionally desired to have single cells as the container unit, most nurseries use some form of cell tray, and increasingly it is common in nurseries to handle groups of cell trays together in growing 1a 1b 2 3 frames. The choice of container is fundamental to many factors affecting seedling growth. Apart from the logistics in the nursery, containers have a direct impact on growth of plants in the nursery. The two biggest factors in the nursery are rooting volume and plant spa- Figure 1: Major early developments in container design were the cing/growing density. addition of basal air root-pruning More important than ease of growth in the (1b) and addition of vertical rootnursery is the impact nursery management training ribs (2). The most recent will have on subsequent growth after plant- designs incorporate side slots for lateral air root-pruning (3). ing. Of these, three factors are the most im- Container design has also evolved portant. They are overall plant balance (size from the long thin shape (SA:D  of plant relative to root volume, as well as 1.0) to more squat shapes (SA:D  1.5).


5

stem thickness), water and nutrient status at time of planting, and the im pact of container design on root form.

Cells shape root systems Containers produce a predictable effect on the shape of tree roots. This is not simply the effect of root growth while in the container, but also the growth effects visible many years after planting. Why not then use this knowledge to design a container to produce a predictably good root form? This is possible, and a range of trays with cells specifically designed to eliminate root shaping is now widely available. These containers all incorporate some means of pruning roots on both the base of the cell, and the lateral roots along the sides. Side slot containers are rapidly becoming the standard for this purpose, although both physical and chemical pruning methods are available as commercial systems for forestry seedlings. The lack of lateral root-pruning features does not necessarily cause trees to fail, but there

Figure 2: Schematic root system response to root-pruning in the container and after planting out.

6


is now considerable evidence to show that root deformation typical of nonpruning container systems is a risk factor to plantation growth and viability. Individual cells, generally of volume 50-400ml 1, have become a common feature for tree propagation. The specific design of the cell, whether grouped together into cell trays or kept as individual units, and the method of manufacture have all changed over the years. Many different designs and manufacturing technologies are used. Root-pruning features Full lateral and tap root-pruning is generally recognised as a preferred feature to be incorporated into container designs. Roots of containerised plants are confined to the rooting volume allowed by the container. Root tips retain apical dominance that suppresses development of a branched root system, provided the root tip remains active. Virtually all commercial containerised propagation systems include air root-pruning at the base of the cell. Options for rootpruning down the vertical surfaces are more varied. Side slot technology extends air rootpruning to this zone too. It is important that the internal cell architecture encourages the root tips to grow towards the slots for airpruning. All root-pruning systems rely on some means of breaking apical dominance, by physical, chemical or air desiccation means. t3np0milg1a

1

Figure 3: Different methods of achieving similar root-pruning results. Physical pruning tends to only occur in bare-root nurseries, air-pruning has been used extensively for many years and requires no regular treatment of containers as is required of chemical methods.

Some argue that cubic centimetres should be used. I have found most growers can visualise millilitres more easily than cubic centimetres, especially in the multiples used in nurseries . 1 cm 3 = 1 ml.


7

At present, chemical and air-pruning techniques are the most commonly incorporated into commercial propagation systems. Air-pruning Air-pruning is effective by creating a barrier to root-growth. The active root tip encounters dry air, dries and dies. This action releases the apical dominance of the root tip in the same way as Figure 4: Note the shaping of the vertical ribs physical cutting will do. The loss of ap- to guide roots to the side slots in this Lannen ical dominance allows new lateral root 63F cell. development to occur. Air movement is necessary to dry the root tips and is particularly import ant in humid environments such as greenhouses. Practical experience has shown that containers need to be suspended at least 200mm above a clear surface to obtain adequate air movement beneath the cell base and up past the side slots. In many nurseries, trays are supported on benches 8001100mm high as a convenient working height and no root-pruning issues arise with this degree of air movement available. Any evidence of roots growing out through the slots or the base of the cells indicates inadequate air movement.

Figure 5: Insufficient air movement around and through the trays allows roots to grow out of the slots. This can cause extraction and planting problems.

8


Figure 6: Dramatic differences in root exposure between copperpruned (L) and unpruned (R) Eucalyptus seedlings.

Chemical pruning Chemical root-pruning has also been used extensively. Successful commercial products have almost all been based on copper salts in a liquid carrier. Commonly, this is copper oxychloride, cupric carbonate or similar powdered formulation of copper applied in a liquid such as a water-based emulsion paint. The formulation is generally applied annually, often as a dip treatment, but increasingly by spray. The pruning occurs because copper ions inhibit growth of the tender root apex and this breaks root apical dominance. This is very similar to air-pruning of the root tip. This pruning of the tips causes development of the desired dense, bushy root system. The copper has to be soluble and in the root-tip zone to be effective. Too much copper results in too much inhibition of the root system, especially prevalent in very small plug containers or where there is limited drainage. Some formulations are made with too much copper available, for example using copper sulphate which is highly soluble in water. Too little copper will result in inadequate pruning. This can occur if there is simply too little


9

copper in the treatment, or when the emulsion liquid carrier forms a barrier preventing any copper leaching from it. I have seen both of these prob lems occurring in nurseries, using both commercial and home-made formu lations. A lack of pruning is clearly evident. A beneficial side effect of many of these copper treatments is the reduction of disease organisms carried between crops on the containers, especially those made from expanded polystyrene. Copper ions are antifungal and antibacterial, and yet appear to have no detrimental impact on mycorrhizae or rhizobia required by many tree species. A few other chemicals have been tested as pruning agents. Various herbicides have shown some promise when incorporated into the plastic during container manufacture. Other metals can also be used, but copper remains the metal of choice as it is readily available, cheap, effective and safe.

Figure 7: Root coiling in a cell with no provision for root-pruning. Note the thickened lateral roots coiling round the bottom and sides of the plug.

10


Other pruning systems Containers can have copper incorporated into the plastic at manufacture. Copper is easily mixed into the plastic, but generally the problem of the plastic completely encapsulating the copper prevents it being available to prune the root tips. Polycaprolactone and related plastics have been used to overcome this problem as they are not entirely impervious to water. These biodegradable plastics are more expensive compared to the other plastics more commonly used for cell trays. Physical trapping of the root system is another means of breaking apical dominance. This system is more common in large containers, especially large volume bags made from geotextile material, or the container methods incorporating other root trapping devices. I am not aware of any plantation forestry systems using this technique as the Figure 8: Root-pruning removes apical containers are small compared to dominance and allows a more fibrous, branched the root trapping devices, but this root system to develop. Once the pruning stops, apical dominance will establish again and system is used in some large pot tree superfluous lateral roots simply wither away. propagation systems for fruit and ornamental trees.

Benefits of root-pruning A branching root system while in the container is an important development. Firstly, a branched root system tends to have a larger number of act ive root tips. These are the sites at which active nutrient uptake occurs, thus more tips mean a better utilisation of nutrients. Secondly, a branched root system binds the growing medium more effectively and reduces dam -


11

age and root distortion during handling. An intact root plug makes handling quicker and less prone to damage of the roots. Thirdly, an active, branched root system tends to allow the tree to re-establish a natural root form after planting out. This occurs because a few of the active root tips will re-establish apical dominance after planting and the non-active roots will die. Mature trees do not have large numbers of lateral roots - those un able to retain their activity simply die and wither away. Containerised plants typically have far more lateral roots than will be retained to tree maturity, thus allowing the natural selection of retained lateral roots to occur after planting. Predictable container shaping with no pruning Where no root-pruning is incorporated into the cell, the initial root tips will retain their apical dominance and will simply circle in the cell as they grow. A sparse root system develops, with few laterals. The growing medium falls away easily. After planting the tree will only have the few existing root tips to continue growing. Nutrients and water from these tips have to move through the spiral system before entering the stem. As the roots thicken, there is insufficient space in the tightly coiled mass and "root strangulation" occurs. The connection between the root system and the stem remains very small and the trees become very prone to snapping off. Similar root development may occur Figure 9: Pine lateral roots shaped by where there is root-pruning only at the base the container into a root cage and the of the cell. Spiral and coiled root systems tips pointed downwards. are less common, especially where roottraining ribs are added to ensure roots are guided downwards rather than around the cell. Lateral roots in these cells take on a typical growth form,

12


Figure 10: Swelling at the root collar and root "strangling" of each other resulting in poor connection between the stem and root system, leading to toppling.

commonly called a "root cage". They grow away from the main tap root, but are deflected by the cell walls downwards at a sharp angle. They can look somewhat like the steel bars of a cage, hence the name (Figure 9). Where full lateral root-pruning is not possible, typical problems after planting out are possible. These are instability resulting in butt sweep, socketing or toppling and appear to become more likely to occur the longer the plants remain in the cells. One possible reason for this time in cell effect is that as the roots become lignified, they lose the ability to produce adventitious root tips and thus outgrow the coiled lateral root system that will have developed. The practical difficulty is that an acceptable time to reduce the risk of permanent root system deformity will vary according to species, climate, management techniques and container volume and design. Vulnerability to toppling is generally highest about 2-3 years from planting out. In general, after this period, the risk for instability diminishes as the deformed component of the root system becomes occluded into the stem/root interface and a new root system becomes fully established.


13

There are two other factors associated with "root cage" root systems. Firstly, a typical swollen root collar zone occurs (Figure 10). This is thought to be related to the constriction in the movement of nutrients between the lateral roots and the stem. In particular, the swelling is caused by an accumulation of photosynthates from the leaves destined for the growing root system. As they accumulate at the root collar, they are not available in the roots for normal root development. Poor root development ultimately reduces overall plant vigour. A potentially more serious problem is that honey fungus (Armillaria sp.) infection of the root collar zone is increased because of the higher concentration of stored sugars in this swollen zone. Furthermore, infection at the root collar is more likely to be fatal than one occurring on the root tips.1 A possibly related effect is the observation that lodge-pole pines with deformed root systems are more likely to suffer fatal consequences when attacked by the Warren root collar weevil. 2 Secondly, "root cage" systems typically inhibit the growth of more firstorder lateral roots. It is thought that increased numbers of these roots is an indication of plant vigour. Any practice that reduces the genetic potential for producing many first order lateral roots will therefore also reduce plant vigour.3

1 2 3

See also Skogen 4/94 pg 15; and Livingston, W.H. 1990. Armillaria ostoyae in young spruce plantations. Can J For Res 20;1773-1778. See Robert, J.A. and Lindgren, B.S. 2010. Root deformation reduces tolerance of lodge-pole pine to attack by Warren root collar weevil. Env Ento 39;476-483. See also Nelson, W.R. 1990. Root pruning can influence first order lateral root development of containerised plants. Com. Proc. Int Plant Prop Soc 49;96-103.

14


Figure 11: Severe socketing caused by wind buffeting the plant which has a poor root form, resulting in toppling.

Cell size, shape and density These three measures have interacting effects on plant growth. Changes in one measure can have implications on the effect of the others, and these effects can be difficult to separate out. Cell size The larger the cell volume, the easier it is to grow plants and generally the better the plants themselves grow, both in the nursery and after planting out. Larger volumes simply having a greater buffer capacity and therefore the margin for grower error is wider. In addition, other physical effects such as the percentage of saturated growing medium caused by the perched water table will be lower compared to smaller volume cells of a similar shape. Common sizes for general plantation forestry plants are 80-110ml volume, smaller sizes for plantation use are 40-80ml volume cells, while large cells used for specific plantation requirements are often 200-400ml volumes. Large plants from these large cells are more commonly used in


15

difficult sites, for example where animal browsing cannot be adequately controlled, or proper weed control is not possible. Small cells are generally used under very good plantation conditions, in which case the cost of plants and planting can be reduced without necessarily affecting plantation performance. Cell shape Cell shape has little impact in the nursery other than its effect on plant density and interaction with the perched water table effect. Shallow cells will show a much higher percentage of their volume affected by saturation after watering. Note also that internal architectural features can have an impact on subsequent plant growth, but generally have little or no effect in the nursery. In general, round cells produce root plugs which are easier to extract, but at the expense of reduced volume compared to similarly spaced square cells, and the increased potential for root coiling. Cells walls are typically 3-8o off vertical. This is an important feature to facilitate removal of the plants. As the plants grow, the roots grow into the volume previously forming the pore space around the growing medium particles. The roots also produce a degree of compaction on the growing medium, pressing the whole root plug against the cell walls. By having the walls at an angle, force is required to dislodge the root plug, but there is no friction force once the initial drag is overcome. Density Density of plants, usually expressed as plants or cells per square metre, is an important factor. Generally, the higher the plant density, the shorter the plants will be when ready for planting out, and they are likely to come from smaller volume cells. High density growing tends to reduce movement of air around the foliage,

Figure 12: Well-spaced plants have leaves down the length of the stem. Plants grown too densely have leaves only at the top, dead leaves lower down can be a source of infection, and stems are often thinner.

16


leading to an increased risk of diseases such as Botrytis. Low light levels will also occur at the base of the plants. Plants grown at high densities lose their lower leaves resulting in "lollipop" growth that can cause problems after planting out. The dead lower leaves can be a disease risk, and poor root collar development will occur.

Table 1: Common specifications for mainstream subtropical and temperate climate plantation species. Specific site requirements need to be considered, but these general guidelines should suffice in most circumstances. Species

Site type

Common plantation conifers and Eucalyptus species, e.g Pinus radiata, P taeda, P patula, Eucalyptus grandis, E nitens Conifers

t3np0milg1a

Planting period

Collar diameter (mm)

Stem height (cm)

Comment

Good, well- Year round prepared, if adequate fertile soils soil moisture

>2.5

15-20

3.5

20-30

4.5 on very difficult sites

30-50

1.5

5 - 10

For ½ / ½ method of bare root system

>3

10-20