Types of Seed Germination, Seed Emergence and Seedling Vigour
The type of germination exhibited by the seeds (seed emergence) of a species influences their ability to emerge from great depths. Seeds with epigeal germination have to push their cotyledons to the surfaced and therefore have limited ability to emerge from great depths.
Moisture Status of the Soil
Under dry condition the seeds should be sown deeper in order to place them in contact with moist soil.
Soil Type
All other factors being equal, seeds can emerge from greater depths in sandy soil than in clay soil. Sowing depth can therefore be adjusted according to soil texture.
Position of Seeds in Respect to Land Preparation
The position at which the seed is sown with respect to land preparation depends on the nature of the crop and climatic factors.
Under waterlogged conditions, the seed is normally planted on top of the mound or ridge so that it is removed from the high water table.
At the other extreme is the situation in dry land areas where planting the crop in the furrow may ensure greater moisture availability.
Placement of Vegetative Propagules
The principles of seed placement in the field are also generally applicable to the planting of vegetative propagules. Because of the large quantity of food that they usually contain, such propagules are capable of emerging from much greater depths than seeds.
As a rule, however, they should not be planted more than 5-10 cm deep in the soil. An additional consideration with respect to vegetative propagules is their orientation. Stem cuttings fail to sprout or perform poorly if planted in an inverted position.
Seed Emergence and Seedling Vigour
Emergence is the appearance of the seedling above the ground. Even though germination occurs only a few days after planting, the emergence of the seedling above the ground is the first visible assurance to the farmer that germination has occurred and that the seedling is now on its way towards establishing itself.
From the farmers standpoint there are three important aspects of emergence:
Time from planting to emergence.
Final percentage emergence.
Uniformity of emergence.
The time of emergence should ideally be as short as possible, so that the seedling can attain independent existence before the seed reserves have been depleted.
Factors Influencing Seed Emergence
The factors influencing seed emergence include the following; temperature, the time to germination, the sowing depth, the nature of the soil, and the Vigour of the seedling.
Time to emergence is usually short if germination is rapid, the temperature is moderate, sowing depth is shallow, seedling is vigorous and the soil is light, loose and free of crust.
The final percentage emergence is the percentage of seeds sown that eventually emerge. It is this percentage that determines the nature of the stand obtained. If the percentage is low, the stand is poor and irregular and the farmer may consider replanting.
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Causes of Poor Emergence
The major causes of poor seed emergence includes but not limited to the following; Poor germination, Very low seedling vigour, Sowing at too great a depth, Attack of diseases and pests, and Extremes of temperature which may severely retard the growth of seedlings.
The Uniformity of Emergence
This indicates whether all the seedlings that emerged did so simultaneously (i.e. on the same day) or whether there was a long period between the early emerges and the late emerges.
Importance of Uniform Emergence
It ensures that all the plants on the field are at approximately the same age.
Operations such as fertilizing and harvesting which depend on timing can be programmed.
Factors Affecting Uniformity of Emergence
Uniformity of germination, non-uniform germination will usually result in non-uniform emergence.
The use of dormant seed can also result in non-uniform germination and emergence.
Seedling Vigour
The seedling vigour assessment is an indication of the health of the seedlings and of the likelihood that they will yield well.
Factors that may lower seedling vigour include the following: small seed size, the presence of pathogens in the seed or in the soil, protracted storage of the seed, and adverse environmental condition during germination.
In summary, the vital role of planting only quality seeds and planting materials in obtaining high yield cannot be over emphasized.
Seeds germination, emergence, and vigour depends on using seeds and planting materials of superior quality as well as appropriate cultural practices such as seed dressing with appropriate chemicals, time of planting, depth of planting, rate of seeding, spacing and position of seeds and propagules in relation to land preparation practices.
The quality of seeds and planting materials plays a significant role in successful crop production enterprises.
The various methods of overcoming seed dormancy and of enhancing seed germination are treated.
Depth of seeding, time of planting, spacing of plants and other parameters that could ensure seed emergence and seedling vigour are covered.
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