The following are the different methods of collection, handling, storage and pre-treatment of seeds before planting operations;
a. Seeds quality
Seeds are collected from ripe fruits on our farms to ensure good seed quality, fruit collection must be made from trees having the desirable characters. Seeds can also be obtained from a known seed source in the country or abroad.
In the latter case, the seed must be of good quality:
Clean from dirt, debris and chaff;
Free from pests and pathogens;
Have a high percentage of germination;
Must be accompanied by a note, carrying the scientific name of the species, place of collection, date of collection, number of seeds/unit weight and whether any treatment has been applied (this condition is important if the seeds are obtained from external sources.)
b. Seed extraction
This is the process of separating the seeds from the fruit. Therefore, the method of extraction varies with the type of fruit. Cocoa seeds are extracted from the cocoa pods.
Whereas the seeds of coffee are harvested from the coffee twigs as single seeds. Both may be planted as fresh seeds.
For cocoa it is mandatory to plant the seed within 24 hours of its extraction from the mucilaginous pulp of the pod.
Oil-palm seeds are extracted from the palm fruit bunches. Kola nut seeds are similarly extracted from Kola fruits.
The seeds of rubber are collected from the field in rubber plantations. Citrus fruits contain the citrus seeds. The citrus seeds need to be extracted from the fruits before they can be processed. Both oil-palm seeds and citrus seeds need drying before further processing can take place.
c. Seed storage
Seeds, whether bought or collected, must be stored in a proper way until needed. Dry seeds can be safely stored in polythene bags at room temperature.
When seeds are stored they are normally labelled, given a number and placed in an air- tight bag.
d. Seed viability
Some seeds lose their viability in a short period, e.g. rubber seeds lose viability in about 6 months; citrus seeds lose their viability rapidly within three months.
Therefore it is important to test seeds which are stored to determine their germination percentage and it is useless to store any seeds that fall below 40% germination unless they are very rare or very expensive.
The viability can be tested through germination tests:
Germination test methods:
i. Filter paper method – where seeds are small, about 100 seeds are germinated in a petri-dish over a filter paper.
ii. Silttest– 100 seeds are sown in a container with silt soil.
iii. Tetrazonium chloride test: This is a chemical that imparts colour to living tissue. The seed is cut and the liquid is smeared onto the cut surface to find whether the embryo is alive.
e. Seedling production
There are many operations involved in seedling production. The most essential ones are described below:
i. Nurserys oil mixtures
Nursery potting soil should have the following characteristics:
- Be light;
- Be cohesive;
- Have good water retention capacity;
- High organic matter;
- Be fairly fertile or made so by the addition of 2 kg NPK/M3 of soil.
In the majority of countries with arid conditions, a mixture of one part sand, one part clay, and one part of animal manure would be adequate. This is called 1:1:1 mixture.
ii. Nurserys oil treatment
Potting soil must be acidic (i.e. pH6). If it happens to be alkaline, it can be acidified by a solution of 2% sulphuric acid.
Sometimes nursery soil has to be sterilized against pathogens by use of a 40% solution of formaldehyde applied as 80 cc per 5 litres of water and applied to the soil 7 to 10 days before sowing the seeds.
Soil fumigation is also a treatment against fungi by methyl bromide gas.
iii. Filling the pots/potsize
Polythene pots of different sizes are now used for raising nursery plants. This does not preclude the use of other containers like boxes, half tins, earth pots, etc.
The pots are filled with nursery soil, taking care to have no voids by shaking and knocking regularly.
The pots are filled, leaving a small space at the top, and stacked side by side on nursery beds.
It is very important to determine the pot size because: large pots require more soil, take a lot of labour to fill and transport; they occupy a large nursery space and require more water in contrast to small pots. But they produce large plants in a short time. The general rule is that “the harsher the planting site, the larger the pot should be”.
The quantity of soil needed in a containerized nursery operation is directly related to the size of the containers used. To fill 100,000 small containers, 28 cubic meters of soil are needed; whereas 442 cubic meters of soil are needed for filling 100,000 of the largest containers (16 times more).
iii. Pre-treatment of seed
Some tree and shrub seeds are ready for sowing as soon as they are collected; others pass through a dormant stage, during which time the embryo completes its development.
Often, a pre-treatment is used to hasten germination or to obtain a more even germination. The methods of pre-treatment vary with the different types of dormancy of tree seeds. The main types of dormancy are:
Exogenous dormancy – associated with the properties of the pericarp or the seed coat (mechanical, physical, or chemical).
Endogenous dormancy – determined by the properties of the embryo or the endosperm (morphological or physiological).
Combined exogenous and endogenous dormancy.
In general, the most frequently encountered type of dormancy in arid zones is exogenous dormancy.
Some of the more commonly used methods of attempting to overcome this type of dormancy are described below.
Mechanical treatment – A small number of seeds can be scarified by scratching each seed with sandpaper, by cutting each seed with a knife, or by sandpapering the end of the seed that is opposite the radicle until the cotyledon is seen.
With large quantities of seed, mechanical scarification can be achieved by pounding the seeds with sand, or by rubbing the seeds over an abrasive slab. A variety of other methods of scarification are also available.
Soaking in cold water – For a number of tree and shrub species soaking their seeds in cold water for from one to several days is sufficient to ensure germination.
The improvement in germination is caused by the softening of the seed coat and the ensuring of adequate water absorption by the living tissues.
When long soaking periods are used, it is recommended that the water be changed at intervals. Usually, it is important to sow the seed immediately after soaking without drying, because drying generally reduces the viability of the seed.
Soaking in hot or boiling water – The seeds of many leguminous species have extremely tough outer coats, which can delay germination for months or years after sowing, unless subjected to pre-treatment by immersion in hot or boiling water.
The seed is immersed in two to three times its volume of boiling water, and allowed to soak from 1 to 10 minutes, or until the water is cold. The gummy mucilaginous exudations from the seed coat are then washed off by stirring in several lots of clean water.
Acid treatments – Soaking in solutions of acid is frequently used in the case of seeds with hard seed coats. Concentrated sulphuric acid (98 per cent) is the chemical used most generally. Most commonly, soaking times vary from 15 to 30 minutes.
After soaking, the seed must be washed immediately in clean water. Tests should be made to determine the optimum period of treatment for each tree or shrub species, and even for different provenances, since overexposure to solutions of acid can easily damage the seed.
Seed inoculation– Legume trees have root nodules which harbour nitrogen-fixing bacteria. When seeds are planted outside their natural range, the soil should be inoculated with crushed nodules from natural stands.
Some inoculum are available on the market which can be mixed with the seeds before germination.
Other treatments – For a number of salt bushes and shrubs such as Atriplex, washing seeds in cold water for one to two hours is sufficient to remove salt from the seeds and improve germination.
The germination process in oil-palm seeds is indeed a combination of the some of the processes described above. Rubber seed treatment is a simple scarification process.
f. Sowing of seeds
Having determined the soil mixture, kind and size of container, one would proceed to sow the seeds.
Depth of sowing: Seeds are sown at a depth of 1-3 times their diameter. When seeds are sown at this depth adequate moisture and optimum temperature will hasten their germination. Excessively deep sowing will impair seedling emergence.
Ideal sowing time: This is determined by the period required to raise a plantable seedling of the desired size.
For example, if it takes four months in the nursery to raise plantable seedlings to be planted in June; then the ideal sowing date for that species and locality is the first of February. Similarly, for planting in October, the ideal sowing date is the first of June.
Watering Plants in the Nursery
After sowing, seed beds should be watered using a fine nozzle spray, producing almost a mist.
Hand watering, whether by a container or with a hose, is the best method of watering. Watering is done frequently until seeds germinate.
Pricking out of seedlings
When seedlings raised in beds and boxes reach the 2-leaf stage, they are carefully picked up using a sharp stick and carefully replanted in pots or other beds.
This is a very delicate process which is now avoided by sowing the seeds directly in pots and thinning the excess seedlings leaving only one good seedling per pot.
Care of Nursery Stock
The production of good quality seedlings will depend on how well the following activities have been executed in its nursery:
Weeds compete for water and soil nutrients. They also block the circulation of air and may harbour insects and disease organisms. Where weeds are permitted to grow in the seedbeds, seedlings will be of poor quality; therefore weed competition must be eliminated.
The methods of ensuring a minimum of weeds in the nursery are: prevention, eradication and control.
Prevention is the practical method. It is accomplished by making sure that weeds are not carelessly introduced in the nursery. Eradication is the complete removal of weeds and their seeds from the nursery.
Control is the process of limiting weed dissemination. Eradication and control are generally carried out as one operation in the nursery.
Pests and Disease-Control
There are many types of pests and diseases prevalent in nurseries of tree crops. When the seeds are carefully selected, most of them may be eliminated. Because of the frequency of watering, diseases related to water and watering may not be ignored. The greatest of them all is Damping-off.
Damping-offis a common and serious disease in many nurseries. It can occur either in seed beds or in containers after transplanting. Damping- off is a pre-emergent and seedling disease caused by various fungi.
Some of these fungi attack the seed just as germination starts, whereas others infect the newly germinated seedlings. Affected seedlings topple over, as though broken at the ground line, or remain erect and dry up.
A watery-appearing constriction of the stem at the ground line is generally visible evidence of the disease. Damping-off is favored by high humidity, damp soil surface, heavy soil, cloudy weather, an excess of shade, a dense stand of seedlings, and alkaline conditions.
One of the best preventive measures for damping-off is to maintain a dry soil surface through cultivation, to reduce the sowing density, and to thin the seedlings to create better aeration at the ground line. The need for soil fumigation is minimized in nurseries where fresh soil mixtures are prepared annually.
Vegetative propagation – Stock planting
Not all trees and shrubs used in planting programmes are produced from seed. Species whose propagation by seed is difficult can often be reproduced by vegetative propagation. Nursery stock that is obtained by vegetative propagation includes stumps, cuttings, and sets.
“Stump”is a term applied to nursery stock of broad-leaved species which has been subjected to drastic pruning of both the roots and the shoot. The top is generally cut back to 2 centimetres and the root to about 22 centimetres.
Stump planting is suitable for “taproot-dominated” species. Frequently, stumped plants are used in sand dune stabilization plantations. Stumps are normally covered with wet sacks or layers of large leaves during transit to the planting site.
“Cuttings” and “sets”are also commonly used as planting stock. A “cutting” is a short length cut from a young living stem or branch for propagating; a cutting produces a whole plant when planted in the field. A rooted cutting is one that has been rooted in the nursery prior to field planting. “Sets” are long, relatively thin, stem cuttings or whole branches.
Size and Qualityof Planting Stock
There is a considerable range in what is considered the desired size of tree or shrub seedlings for planting.
The optimum size varies, depending on whether the seedlings are bare-rooted or containerized, on the tree or shrub species to be planted, and on the characteristics of the planting site.
In general, it is agreed that plants with a well-proportioned root-to-shoot ratio represent good planting stock, but it is difficult to define an “optimum” root-to-shoot ratio. A root- to-shoot ratio based on weight might give a more accurate measure of balance.
Stem diameter and height are other criteria for evaluating planting stock that might allow the setting of minimum acceptable limits.
Experience indicates that medium-sized stock, between 15 and 40 centimeters, with a woody root collar, have a better survival rate that do smaller plants.
The maximum size for planting potted stock is largely determined by the size of the container. The larger the containers, the larger the plant that can be grown in it; but the period of growth is limited to that free of harmful root restriction.
Excessively tall plants can be lessened in the ground or blown over, and root development might be restricted or inadequate to cope with the high transpiration demand of a large top.
Preparation of Seedlings for the Planting Site — Hardening-Off
Seedlings continue under nursery care while they develop for 2-3 months. Then the good ones will be selected and placed in separate beds.
They are given less water and exposed to the sun gradually to condition them for planting in the site. This hard treatment is called hardening-off. Seedlings will develop a dark green colour and look healthier in the open than under nursery shade.
Seedlings of plantable size are first graded. The grading of planting stock depends, to a large extent, on local experience and the establishment of local standards.
The main objectives of a grading system for planting stock are:
To eliminate culls, seedlings with damaged or diseased tops or roots.
To eliminate seedlings below minimum standards of size and root development.
To segregate the seedlings that exceeds the minimum standards into two or more quality classes.
Before seedlings are to be transferred to the field where they are to be planted into their permanent site, they are usually prepared for the situations they are to meet on the field.
Some of the conditions on the field may include: inadequate water supply from irregular rain, severe and intense sunshine (when compared with the situations in the nursery).
The areas where the pre-transplanting operations are concentrated are:
Pests and disease control.
Root treatment:In crops that are to be uprooted from the main nursery, the roots are usually disturbed during transplanting operations.
Crops that are budded or grafted stay in the nursery for about three to four months before they are ready for transplanting.
When it is established that budding or grafting has succeeded, the next stage is to prepare the crop for transplanting into the field. Where the crops are not planted in pots or polythene bags – i.e. they are planted into the main nursery bed, root treatment is definitely required.
Using the main stump as the centre, draw a circle of radius 6 – 8 inches (15 – 20 cm) round the stump. Divide the circle into two equal halves by drawing a diameter through the circle.
With the aid of a sharp cutlass or spade cut the roots along the first half of the circle to a depth of 12 – 15 inches (30-40 cm).
Three days to the intended date of transplant of the crop, cut the other half of the circle to the same depth of 30 – 40 cm.
The purpose of the cutting of the roots in each of the semi-circle is to induce root formation in preparation to field transfer.
On the due date for the transplant, uproot the crop seedling along the cut circumference and lift the seedling with the ball of earth that is 6 – 10 inches in diameter.
Where transferring with the ball of earth is very difficult, deep the roots in clay slurry so that the roots will notbe naked.
Shade Treatment: Since the seedlings will be exposed to more harsh condition of heat and sunlight when they are transferred to the field, it is often better to gradually expose the seedling to this type of situation.
This is achieved by gradually expose the seedling to this type of situation. This is achieved by gradually reducing the shade in the nursery over a period of 4 – 6 weeks. The seedlings should experience zero shade for about a week before they are transferred to the field.
Water stress is critical in some crops. Crops/seedlings to be transplanted should he heavily watered a day previous to the transplanting.
Freckleis a common disease on palms which is induced by water stress. Seedlings to be transplanted should be treated of all diseases and should be disease-free. Similarly, they should be free of all pests and pest eggs that will hatch later.
Transporting Seedlings to Field – Planting Site
Packing of container-raised plants for transport presents few problems. They are put in trays and loaded into vehicles. The tins which have been used for seedling trays can be used for transporting container plants. Sometimes wooden trays are used, but these are heavy.
Often, plants are damaged during transport to the planting site. Therefore, adequate care must be taken to avoid mishandling of plants during loading and unloading from vehicles.
Something that is often forgotten is that plants require protection during transportation, as the air-flow can cause drying. It also is important that the containers are packed tightly, so that they cannot move.
Special shelves for stacking pots or trays can be added to the vehicle platform (each layer of trays being placed on a shelf, with one shelf about 50 centimeters above the other). When possible, plants should be transported in the planting season on cool, cloudy, or even rainy days to prevent desiccation during transport.
Shipping schedules should be planned to avoid delays and to allow proper disposition of the plants immediately upon arrival.
Normally, plants should arrive one day ahead of planting; where shade and watering facilities are available; supplies can be brought several days in advance. As soon as the plants arrive at the planting site, they must be watered and, if necessary, heeled-in in a cool, moist, shaded place until they are needed for planting.
Organization of Seedling Production (Summary of Nursery Operations)
Seedling production must be organized in such a way that plantable seedlings of good quality are produced in time.
As time of planting is critical in deciduous areas – except when irrigation is applied – the organization becomes very important.
All the processes which have been described earlier must be done perfectly and on time. These activities include;
- Seeds and their treatment;
- Soil mixture;
- Filling of pots;
- Picking out;
- Provision of shade and shelter;
- Hardening off; and
- Transport to the field planting site.
Only the number which can be planted in one day should be removed from the nursery to the site. According to the planting programme seedlings are hardened off and transported.
The number of plants raised originally in the nursery is about 20% more than that planted in the field. This is to make up for culling and a reserve for replacing dead plants.
Administration is also very important in nursery work to ensure that:
Nursery activities (jobs) are done correctly;
These activities are done in time;
Labour requirement is available (man-days) for performing the work; and
Materials/tools and equipment required to do the work are suitable.
This requires a nurseryman having a fair knowledge of labour productivity, nursery technique and prices of materials. Records of nursery seedling production as well as costs of materials and labour are kept to show the economics of nursery operations.
Labour and material requirements depend on the size of the nursery.
Forms showing cost of tasks, e.g. seed collection, filling of pots with soil, sieving, mixing and preparing nursery soil, should be designed and filled-in regularly.
Read Also : Complete Waste Management For Restaurants