Seedlings Management Practices
Tree species differ in their requirement of shade to germinate. Shade bearing species require heavy shade to reduce temperature and keep the soil moist and fresh. Light demanding species like Tectona grandis and Gmelina arborea do not necessarily need shade to germinate. Shading is provided for small seedlings sown in boxes or trays in the Savannah zone but not usually for pricked out seedlings or seedling raised by direct sowing into containers.
Mulching or spreading insulating substances over the surface of the soil can be used in place of shading. It regulates soil temperature and conserves soil moisture by reducing evaporation through lowering of the soil temperature and by increasing the absorptive capacity in the upper layers of the soil. It also controls weeds and reduces erosion by encouraging infiltration and decreasing surface run off.
Water is vital to seed germination and seedling growth. The seed or seedling environment must be kept adequately moist through irrigation where natural watering conditions are not adequate. The frequency and amount of irrigation depend on the climatic conditions in the nursery the rate at which water is absorbed by the roots and the water holding capacity of the soil in the root zone.
Scanty irrigation encourages deep root development while excess (flooding) reduce drought resistant and cause seedlings stagnation as a result of insufficient aeration. A balance between excess and scare irrigation will produce the optimum seedling.
Three nursery irrigation methods are currently in use. They include surface, sub-surface and sprinkler irrigation systems. In surface irrigation or flooding, the water is distributed either by flooding the entire surface or restricting the water to some type of furrow. In sub-surface irrigation, the water flows under ground as a controlled water table over an impervious substratum and provides moisture to the seedlings by upward capillary movement. It involves creating and maintaining an artificial water table where soil is permeable enough to allow lateral and vertical water movement. In fadama areas and around the Lake Chad such water tables exist naturally. Both manual and mechanical sprinkler irrigation involve artificial simulation of natural rainfall on the seedlings.
Weeds compete with seedlings for moisture, mineral nutrients, space and light. If left unchecked they may stunt and even kill the plant. Movement of soil (tillage) during weeding also improves infiltration, aeration of the roots, absorption of water and reduces run-off and minimizes soil erosion.
Chamshama and Hall (1984) observed that a simple way to promote growth and yield of trees in plantations is to produce and use strong healthy planting stock. This can be achieved through the use of fertilizers to improve soil fertility and consequently promote strong healthy seedling growth.
On the entisole of north- eastern Nigeria results of experiments suggested the ideal fertilizer rates to be 30-90kg/ha, 30-60kg P/ha and 60-90 kg K/ha for rapid growth and high yield of mahogany seedlings. Single application of N or P produced maximum tree yield at the rate of 30kg N or P/ha while single K did so at 60 kg K/ha. Where N and P were applied together, 60 kg N/ha and 60 kg P/ha gave maximum tree yield. Combined application of N and P produced superior yield on pots with 90 kg N/ha and 30 kg K/ha. The best combination for P and K was 30 kg P/ha and 30kg K/ha, while 60 kg N/ha, and 90 kg K/ha produced the highest mahogany seedling yield where all the three fertilizers were applied.
Rapid seedling growth implies rapid availability of strong, healthy planting stock. It also implies less time spent at the nursery. This is particularly important in these semi-arid areas where resources, such as water for long time (extended) seedling irrigation, are very scare. The application of fertilizers would improve the quantity of seedlings and enhance implementation of afforestation programmes.
Roots of both bare-rooted and potted seedlings need to be pruned regularly to restrict their extensive development or to change their rooting habit, especially the tap root. Root pruning involves severing the tap-root and the lateral roots as well. The aim is to restrict the tap-root development and to encourage the seedling to develop quickly after planting it. Shoot pruning of seedlings is also practiced as a means of checking the growth of seedlings that tend to grow tall, thin and weak.
Seedlings in beds or rows can have their roots pruned or undercut in situ as an alternative to transplanting. In containerized seedlings, root pruning involves cutting off the roots that have grown through the pots.
In the tropics, the occurrence of the wet season usually determines when planting should be done. Evapo-transpiration stress at planting is the main cause of death and is minimized by three practices.
- Plant seedlings when soil moisture levels returned to field capacity, this is often only after about 100mm of steady rain has fallen and the wet season commenced.
- Plant on cloudy days.
- Use well- balanced and conditioned plants which have been well watered just before leaving the nursery.
In arid regions it is safest to use container stock and to plant when there are heavy rains during the period they are most expected. However, this time for tree planting coincides with sowing and planting of food crops by villagers and farmers, a conflict which needs to be recognized and allow for, particularly in social and community forest project.
Laying Out Planting Positions
There are consideration alignment of rows and spacing between trees. Row alignment should fit in with the intended extraction system and be at right angles to the main extraction roads and tracks in a compartment road and tracks mostly follow the contours, rows run up and down slopes.
There are many methods of marking the planting position to ensure regular spacing of trees. It is important that the method is simple, easy to apply, and practicable on the kind of terrain encountered. Extreme precision is not necessary. Clearly visible rows and evenly spaced trees are quite adequate.
Two patterns are commonly used, square planting, where distance between trees is the same along and between rows, and rectangular planting where trees are closer in the row than between rows. Rectangular planting patterns may be done to aid machine access, allow food crops to be cultivated between the trees, or where trees are planted in spaced lines in enrichment planting or to avoid complete clearance of vegetative cover for protection reasons. Most tick plantation follows this pattern of planting. The number of trees planted per hectare (stocking), is one of the most important silvicultural decision in plantation establishment. Wider spacing than 5x5m is largely confined to agro forestry. Spacing affects plantation yields, tree sizes and growing cost and revenue. Overall, more widely spaced plantations are probably cheaper to grow. At closer spacing cost were higher due to both greater planting costs and weeding cost because of less opportunity for mechanized weed control.
The effect of spacing on revenues is complex. Spacing directly influences total volume production and tree size, but in summary:
- Wider spacing reduces total volume production, especially in short rotation, since for a longer period a site is not fully occupied.
- Wider spacing increases neam tree size.
- Wider spacing tends to increase stem taper which may reduce the percentage conversion when the log is sawn.
- In broad leaved stands wider spacing usually results in trees of poorer form, with larger crowns and less strong apical dominance.
- With wider spacing, there are fewer final crop trees to choose from. Many broad leaves require close spacing to assist upward development and reduce overly spreading crowns such as teak and iroko.
Bare-rooted plants and stumps can be planted in a hole or slit dug with a spade. Container plants are planted in a small pit. Planting is an important operation and deserves been done carefully, poor practices hastily carried out can lead to high mortality even with robust species like teak. For all planting the following general rules apply:
- Insert roots into the soil up to the root collar.
- Avoid damaging roots by breaking, blending or crushing.
- Firm soil around the roots using ball of the foot.
- Remove impervious container before planting. However, in termit-infested sites, plastic sleeves are slit but left in place around eucalypt seedlings as a protective barrier.
On day sites the planting position should maximize water retention, e.g. furrow bottom, based of mound or micro- catchments.
- Stump plant should not be forced into the ground. They should be placed in specially prepared holes and the soil firmed around them as with ordinary plants.
Fire protection is especially important on dry grassy sites since young trees soon die if burning occurs. Provided there is adequate weed control which reduces fire hazards. No other special protection measures are applied to young trees. Fungal infections are uncommon, provided cultivation, weeding and fertilization are satisfactory. Two most serious damage to young seedlings are from animal and insect attack.
Animal damage to small trees from burrowing, transplanting, breaking and rodent gnawing bark can be a serious problem. This is most acute in dry countries with sparse natural vegetation where animals turn to planted trees for food. Goats, Carmel, sheep, and cattle in sahel, Sudan and guinea zones of Africa are perpetual obstacle to afforestation programmes. Protection includes errection of fences and walls and use of Shepards and herdsmen may be the only solution.
Insects can destroy newly established plantations. In many parts of the tropics, especially Africa, termites attacks are the most common problem. A protection against termites is most important for eucalypts, pines and Gmeline. Plant extract such as “azadiracttan” from Neem azadiracta indica, mulching with foliage of certain species and surrounding newly planted trees with Euphorbia have all been found to contain some insecticidal properties.h