Seeds are to be tested before use or sowing in the beds or fields as the success or failure of artificial regeneration work depends on the quality of seeds. When the treatment is given before sowing in the field, it is called pre-sowing treatment. If some species of seeds are not treated, germination may be delayed or germinate irregularly. And in order to hasten germination of such seeds, they have to be given treatment. Why seed treatments are necessary as :
- To determine genuiness: Genuiness of seeds means purely desired seeds for producing plants in the beds, not mixed. Identification of such seeds is necessary. Sometimes, it is very difficult to identify the seeds. In such cases, it is necessary to collect a botanical specimen of the seed bearing plant and get it identified by an expert botanist.
- To determine purity: Seeds may have other foreign matters, even if they are genuine. For the purpose, seeds are cleaned by winnowing or hand-picking. If samples of cleaned seeds are compared with the collected seeds. Purity can be determined easily.
- To determine seed viability: Viability of seeds are can be determined by direct inspection or by physical or chemical test. Short viability (not more than three weeks) are for Shorea robusta, Artocarpus lakoocha. No doubt, viability by direct inspection is rough estimation mostly done by nepalese farmers. By the inspection, seeds having hollow, insect-eaten, mouldy or otherwise obviously bad are excluded as unviable. Physical test, which is done by winnowing or submersion in water. Similarly, chemical test may be done by using chemicals such as Indigo carmin in 1:1000-2000 has been reported to be the most useful. Some kinds of chemicals discolor the seeds whether their parts are genuine or not. If they are not genuine, their color becomes changed.
- To test germination capacity: This type of test are practically done in the tray or beds, the germination is found out.
Methods of seed treatment before sowing in the beds
- Weathering: Weathering means exposing the seed to sun, wind and rain to crack its hard coat. When germination is seen to be just starting, the seed is spread out on mats to be exposed to sun, wind and rain. The seed is then dried in shade and bagged for sowing in the following rainy season.
- Water Treatment: In water treatment, water either cold or hot, is used to hasten germination.
- Soaking in cold water for 24-48 hrs before sowing: This treatment is applied to most medium-sized dry seeds, eg., chir pine and many leguminosae species.
- Soaking in boiling hot water: Water is heated in a tray and then seeds are kept in hot trays just after removing from stove so as to crack the seed-coat, eg. Albizia, Oaks and chestnut. By this treatment, insects may be killed, if any.
- Alternate wetting and drying: Nursery bed process and Pit process It can be done either in nursery beds or in the pit of specific size (0.8m deep and 1to 1.2m square). In nursery bed process, 5mm thick layer of sand is laid and then covered with grasses and watered sufficiently. After 12 hrs, the grass is removed so that the seeds are exposed to sun and dries. Again, the grass is put back on seeds and watered. This continues for 2-3 weeks, when the seed starts germinating. Similarly, in the pit process, bottom and sides of the pit are lined with teak leaves. Seed soaked in water warmed by sun during the day is placed in the pit separated by teak leaves of 6-10mm thick. After some layers, bamboo pipes are kept. The seeds are kept in the pit for about 10 days and watering is done every alternate day. The pit is then opened when seeds are expected to have germinated. Heavy watering must not be done.
- Passage through animal body: Some seeds germinate quickly if they are passed through the digestive system of the animals or poultry, eg., Acacia arabica, Santalum album, etc.
- Mechanical Treatment: It refers to the mechanical cutting or filling of the hard coat of seeds so that moisture may reach inside. It is beneficial if fruit has 2 or 3 seeds, eg. Rudraksha, Lapsi, etc.
- Chemical Treatment: Chemicals such sulphuric acid, sulphate of magnesium, etc are used to soften the seed-coat and renders them permeable to water.
- Scorching or fire treatment: A fire through the teak forests stimulates germination. Therefore, the teak seed is sometimes spread on ground on a layer of leaves and given a light burn. But it is now not being used practically as this method is difficult to control.
- Stratification: The seeds are spread in layers of 1-2 cm deep altering with layers of sand, or charcoal about 5-7cm deep in boxes or baskets, stored in pits dug in the ground. This method is suitable in higher hill forests.
- Fermentation: This method has been successfully used for teak. For this, seeds are spread on ground covered with grass which is kept moist. Fermentation is induced by adding innoculum for a cattle shed or drain. The bacterial action is allowed to continue for about 2 months when the seed is ready for dibbling.
Soil management and use of manure
Temporary nursery located in recently felled area or new good fertile site need not be manured but for permanent and semi-permanent nurseries, Manuring is quite essential. For this, Organic manure, Commercial fertilizers or Mycorrhiza are applied based on the qualities of soils. Additionally, other types of innoculationmay be needed to produce large quantities of healthy seedlings.
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