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Literature review
content studies involving organic soils, some inaccuracy is probable. In such cases
some of the observed decrease in weight may be caused by changes in the
composition of the organic matter (GARDNER et al., 1991)
Field capacity is defined as the soil moisture content where gravitational drainage
ceases in a soil that was saturated with water (DONAHUE et al., 1983). Wilting point
is defined as the specific soil moisture content at which the plant can no longer
absorb water. The water available to the plant can thus be calculated by the
difference between field capacity and wilting point (DONAHUE et al., 1983).
2.6.2 Organic matter
This includes living, dead and decomposed biotic matter (DONAHUE et al., 1983).
Soil organic matter is a very important factor in soil fertility (DONAHUE et al., 1983).
It is a reservoir of essential plant nutrients, including nitrogen and phosphorous. Soil
organic matter also loosens up the soil to provide aeration (DONAHUE et al., 1983).
2.6.3 Soil nutrients
Sixteen chemical elements are known to be important to a plant's growth and
survival. The sixteen chemical elements can be divided into two main groups, non-
mineral and mineral, according to chemical structure. The non-mineral nutrients are
hydrogen (H), oxygen (O), & carbon (C). The mineral nutrients are divided into two
groups; macronutrients and micronutrients (See Table 2.2). The macronutrients are
considered to be the nutrients essential to plant growth.
Table 2.2: Classification of mineral elements into macro- and micronutrients (Modified from
(MARSCHNER, 1995)).
Classification Element
Macronutrient N, P, S, K, Mg, Ca
Micronutrient Fe, Mn, Zn, Cu, B, Mo, Cl, Ni, Na, Si, Co
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