All about potatoes.pdf - Vegetableipmasia.org

3.
SOIL
3 SOIL
3.1 Soil ecology
What do we imagine when we hear the term soil? Something made up of piles of
dead creatures possibly, or leaf litter, sand or dust. However, soil is much more than
that. Soil can be called a living entity, because within it there are millions of different
living organisms. Some are large and visible; others are so small that we cannot see
them with the bare eye. Examples of larger ones are white grubs, mole crickets,
crickets and earthworms, while smaller ones are fungi, bacteria and nematodes. The
total mass of living organisms, including plant roots in a 20 cm deep area of soil
covering one hectare is around 5,000 – 20,000 kg.
The living organisms in the soil interact with each other, in that some are mutually
beneficial, while others are detrimental to one another. Mole crickets and white grubs
are pests that attack plants, roots and tubers under ground. Some bacteria and fungi
cause plants to become sick; while other bacteria and decomposers break down
plant remnants turning them into fertile humus.
Soil that contains no living organisms will become degraded as leaves cannot
decompose and are left to pile up on the soil surface. They will not decompose and
form the nutrients that plants need.
Soil is a vital resource that must be preserved to support farming sustainability. In
order to maintain life in the soil:
• Organic matter must be kept and added when necessary, as it can increase the
diversity, quantity and roles of beneficial living organisms.
• Contour crops, cover crops and build terraces to prevent soil erosion.
• Soil must not be polluted with pesticides. Pesticides kill off beneficial organisms
and can upset the soil’s ecological balance.
3.1.1 Soil types
Soils are composed of three essential minerals – sand, clay and loam. There are
three classes of soil:
• Clayey soil. Made up mainly of clay and silt, it is difficult to work when dry, is
tough, and does not absorb water easily.
• Sandy soil. Dominated by sand and characterized by its ability to absorb water
and be worked easily. This soil type can lose its organic content easily, so a lot of
organic matter must be added in order to maintain fertility.
• Loamy soil. The most prevalent component is sand, but this is balanced with clay
and silt. Loamy soil usually has the good characteristics of clay and sand; it has a
friable nature, the ability to hold water well and is fertile. This soil is often found in
mountainous regions or on the slopes of volcanoes. Loamy soil is suited to all
crops, and particularly to potatoes.
You can determine soil types by doing a "Sediment test":
• Put soil samples into clear bottles,
• Add water at a ratio of 3 parts water to 1 part soil,
• Shake the bottles until the water and soil are thoroughly mixed together,
• Leave to settle,
A HANDBOOK TO THE ECOLOGY AND INTEGRATED MANAGEMENT OF POTATO 5