Page 43 - Agriculture_Form_Three

Chapter

Two

Chemical properties of soil

Introduction
In previous classes, you learnt about physical properties of soil and their importance
in agricultural production. In this chapter, you will learn about the concept of chemical
properties of soil, soil colloids, ion exchange, soil pH and carbon to nitrogen ratio
in relation to soil fertility and productivity. The competencies developed from this
chapter will enable you to manage soil properly so as to attain maximum returns
from soil.

The concept of chemical properties of soil

Chemical properties of soil can be described as interactions of various chemical
constituents that take place among soil particles in the soil solution. The levels and
availability of nutrient elements to plants is an essential component of chemical
properties of soil. Thirteen (13) out of sixteen (16) nutrient elements are obtained by
crop plants from soil mineral or organic matter and they can be restored by application
of manures or fertilisers. All these nutrients are taken up in ionic forms from the

soil solution as cations or as anions. These include nitrogen (N), phosphorus (P),
potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), iron (Fe), manganese
(Mn), zinc (Zn), boron (B), copper (Cu), molybdenum (Mo) and chlorine (Cl).
Three (3) out of the sixteen (16) nutrient elements are obtained by crop plants from
air and water. These nutrients are carbon (C), hydrogen (H) and oxygen (O). Even
though we don’t apply manure or fertiliser materials to the soil in order to supply
carbon, hydrogen and oxygen; soil management practices affect their availability.
The basic factors related to levels and availability of nutrient elements to plants
include soil colloids, ion exchange, soil pH and Carbon to Nitrogen ratio. These

factors are discussed in the following sections.

Soil colloids

You have learnt in previous classes that soil consists of solid particles of different
sizes which are generally large, intermediate and very small or mixture. Some of
those particles are clay and humus. Clay and humus particles are very small in size.

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