Seed Sowing

Most of the seeds do not need per-treament. Certain species with hard seed coat, however can be germinated more easily by treating the seeds.

Table 1

It is better to pre germinate the seeds of species with slow or irregular germination viz., Tectona grandis, Terminalia tomentosa, Pterocarpus marsupium etc., in trays or beds and then sow the pre germinated seeds in nursery beds so that the germination is completed and there are no gaps in the nurseries. This is also done when the seeds of Dalbergia sisso are sown in spring when the soil temperature is low for proper germination or when species with minute seeds viz., Eucalyptus species are to be raised singly in poly pots.

Sowing of seeds in seed or germination beds is generally done by hand and only with some practice, sowing of seeds can be done to the desired uniformly and thickness. If available, seeding trough may be used to achieve uniformly in sowing. Broadcast sowing is done for smaller seeds after mixing with some quantity of sand to facilitate uniform seed germination. Seeds are sown in drills which are made with the help of a drilling board. In order to make the drills, the board is put on one of the nursery bed and pressed. This results in small drills on the bed. The board is then lifted up and put on the adjacent part of the bed to make drills there. Seeds can be sown directly in containers if they are of bigger size since the germinated seedlings from large sized seeds are larger and may have more mortality during pricking out from the seed beds which is avoided by this method.

The seeds are generally sown in lines, the distance between the lines depends upon the seeds sown. Usually, the lines are made at 15 to 20 cm apart and the seeds are sown 3 to 5 cm apart. The depth of sowing should be 2 to 4 times the diameter of seeds, ensuring that the seeds are just covered with the soil intuit. The seeds should not be sown very deep because the germinated seed has to push its tender shoot through that much of soil, in which process it may die. They should also not be left on the surface of the bed. The seed should normally be sown in such a manner that the depth of the soil above it is not more than the minimum diameter of the seed. If the seeds are known to have a comparatively long germination time, the sowing should be deeper, though the soil cover should be over compacted. Just after sowing the seeds, mulching by covering up the soil with paddy straw or similar material is helpful. Care should however, be taken that straw is not attacked by termites.

Seeds of many species are non nodulated and therefore may not be able to fix atmospheric nitrogen. The Rhizobium which has the distinction of fixing atmospheric nitrogen can be introduced in certain species through inoculation of seeds. Rhizobium available in the market is mixed with water and made into a slurry. The seeds are heaped and inoculum is added to it thoroughly with a shovel. The seed are then sprayed with a thin layer of inoculum under shade and sown as soon as possible. To avoid these loss of seeds by ants, lime or rock phosphate is used as seed coat. Moderate supply of moisture and optimum light are conductive for Rhizobium growth in the soil. The Rhizobium can be inoculated with the seeds or species like Acacia, Bauhenia, Leucaena etc.

When a species which has mycorrhiza in its roots is to be raised in nursery its natural habitat, it is necessary that appropriate mycorrhiza is introduced in nursery soil for proper development of seedlings. Introduction of mycorrhize is done by mixing the soil brought from natural good quality forests of the species. The soil should be neither dry not very moist but should contain adequate moisture as well as mycorrhiza roots. It should be brought in sealed polythene bags and applied to the site as early as possible, but not later than 10 days after collection pt ensure viability of mycorrhiza. Introduction is also possible by inter planting imported seedlings with mycorrhiza in nursery beds. Mycorrhiza are seen in the species like Casuarina, Sandal, Podocarpus, Eucalyptus.

The quality of seeds to be sown in each bed depends upon the size of beds, weigh of seeds, spacing of drills, spacing of the seeds in drills and the plant per cent. It can be roughly calculated by the formula,

W = ( A X D X 100 ) / ( P X N )


W = weight of seed required in gram,

A = area of bed in square meters,

D = number of plants required per square meter,

P = plant per cent of the species,

N = number of seeds per gram.

In practice, twice the quantity of seeds should be used for drill sowing and six times for broadcast sowing.

Time of sowing depends upon various factors like time of seed ripening, the rate of growth of species, size of the plant to be planted out etc. If the size of the plants to be planted out is small and the seed ripens in winter, spring sowing can give plants fit for planting during rains. But where tall plants are required for planting, or where stumps are to be made, seeds are sown in rains to give plants or proper size by rains.

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