An e-publication by the World Agroforestry Centre |
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AGROFORESTRY EXTENSION MANUAL FOR KENYA |
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9. TREE PROPAGATION METHOD 9.3 Direct seed sowing at the desired site Another simple way of getting more trees on a farm is to sow the seed directly at the desired site. This is an important method for species and technologies which require very many trees or shrubs, e.g. live fences or dense woodlots. A good seed supply is a must for this method since normally a certain amount of seed will be wasted. Normally, directly sown seedlings cannot be as well cared for as seedlings in a nursery, and one must also expect accidents, e.g. seeds being washed away by rain, being eaten by birds, or young seedlings being mistaken for weeds and removed. Occasionally there may be a dry spell soon after germination and if watering cannot be easily arranged such a dry spell may result in almost total failure. It is then necessary to have access to plenty of seed so that the sowing can be repeated. If wildings are available in the surroundings but not growing exactly where they are wanted, they can be uprooted and transplanted to the desired site. If wildings of a certain species are wanted, the area under a seeding tree can be cleared of weeds and the soil loosened to help the seeds to germinate. When the rains start, the seeds will germinate and the wildings can be collected soon thereafter. Wildings can be collected when they are very small, e.g. with only two to four leaves. However, such a small wilding requires good care, including weeding, after transplanting, and therefore it is more common to transplant bigger wildings of up to 25 cm. If bigger wildings are transplanted, they must be carefully uprooted, leaving soil around the roots, and planted on the farm in the same way as seedlings from a nursery. Farmers already use wildings of very many species, both exotic and indigenous. Grevillea robusta and Cordia abyssinica are examples of species commonly propagated in this way.
Direct-seed sowing is a method that can be used both in high-potential areas and in ASAL areas. The risk of failure is, however, higher in dry areas where rainfall is erratic, but often it is still worth trying. In dry areas, it may be necessary to repeat the sowing several times, but it is still justified since the cost involved is small. Use of seedlings may be a safer method in ASAL areas, but if many seedlings are required the problems of raising and transporting them and still having to expect a relatively high mortality makes it uneconomical to use seedlings on a large scale. Criteria for species and technologies where direct-seed sowing is recommended are:
Some species and technologies that meet most of the criteria are:
It is rarely justifiable to raise any of these species in nurseries. Apart from climatic factors, sowing depth is a factor which frequently causes problems when directly sowing trees or shrubs. If seeds are sown too deep, the seedlings may not reach the soil surface after germination, and if they are sown too shallow the risk of the seeds being washed away by rain increases as well as the risk of drying out during germination. As a general rule, a sowing depth about twice the seed diameter can be recommended. It is also important that sowing be done as soon as the rains are well established to give the seedlings time to grow as big as possible before the dry season. If there is a dry spell, a little supplementary watering may make a big difference to survival. Weeding is even more essential after direct seed sowing than with any other tree-planting method since the seedlings are very small initially. |