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Soil collection

Soil collection and mixing is vital in nursery operations. This is because the soil collected will be used by the seedling for nutrient and support for quite a long time.

It is very important to select an area with good soil. The existing vegetation of a place can assist in making a judgment if an area has good soil or not. For example, areas with a lot of vegetation indicate fertile soils but areas with less vegetation or vegetation with stunted growth might indicate poor quality soils.

The soil must be rich in nutrient. The soil is dug up to about 20 cm deep, or at the depth where there is good topsoil,  using hoes (Jembes in Swahili) after scraping off the vegetation.

It is best to collect soil three months before potting so that organic matter can decay and the seeds of weeds can germinate and can be removed easily. However, if time does not allow, one can use the collected soil immediately for potting.

After collecting the soil, ensure that it is free from roots, stones, and other substances. Ideally, this can be achieved by sieving the soil.

Soil mixing

Soil mixing is a regular activity in the nursery. The main purpose of soil mixing is to improve the nutrient and drainage of the soil.

To on improve the nutrient, the soil is often mixed with manure. The manure should be fermented NOT fresh!

Sand is added to the soil to improve drainage, especially to clayey soils. Sand is added to allow air and water to infiltrate.

Soil is usually mixed in ratios. The ratio to be used will depend on the type of soil collected. A common ratio for clayey soils in sub-Saharan Africa is 5:2:1 meaning five parts soil to two parts manure to one part sand. Soils with good drainage e.g. loam do not require sand, the ratio, in that case, could be 4:1, meaning four parts soil to one part manure.

It is good to ensure the soil is evenly mixed through thorough overturning.

Potting

The polythene tube 4” by 6” is commonly used as planting pots but 5” by 7” are also good especially for indigenous seedlings that stay in the nursery for a long time. Also locally available materials such as tins, tetra packs, milk packets boxes, etc. can also be used for potting. It is better to use open-bottomed than closed containers since this allows healthier root development and possible root pruning. If tins or other containers are being used, it is important that holes are made in the bottom to allow the movement of water.

The pots are then filled with the mixed and if possible sieved soil. When filling the pots with soil, ensure that the soil is not too compact.  After filling the pots with soil, they should be properly arranged in the nursery. The proper arrangement makes counting of seedlings or pots easier.

In dry areas, it is good to make sunken beds to conserve water

Following the correct procedures in soil collection and mixing in a tree nursery ensures that the substrates for supporting seedlings is of high quality.