Dr Pieter Swanepoel
Department of Agronomy, Stellenbosch University
F
armers have come to understand that agriculture
should not only be high
yielding, but also protect
the environment. This means that
both sustainability and continuous
production from soil should be ensured. Conservation agriculture (CA)
can be viewed as a combination of
management practices that ensure
more sustainable agriculture. According to the Food and Agriculture
Organization’s (FAO) definition, CA
is characterized by three management principles. The first is following a reduced soil disturbance regime, the second maintaining a soil
cover (either live as cover crops or
dead organic material as mulches),
and the third cultivating diverse
crops in sequences. These three
principles directly and fundamentally relate to soil conservation. International experience suggests that
soil quality improves significantly
following the adoption of conservation agricultural practices. In simple
terms, soil quality can be defined as
the ability of the soil to function,
which include chemical, physical
and biological processes. It is upon
soil quality that plants rely to sustain productivity.
Reduced tillage
It has been shown that continued
conventional tillage operations have
a profound negative impact on soil
quality. This is because soils are
alive. Hundreds of thousands of soil
microorganisms could flourish in a
mere few grams of soil. The environment for microbial activity differs within only a few centimeters
of soil along the depth profile, usually highly stratified profiles skewed
to the soil surface. This means that
organic matter and its related factors, nutrients, texture and soil
pores (gaseous exchange and water
availability) are highly concentrated
towards the soil surface, and lesser
so deeper down into the soil. When
these different horizons are disrupted and modified by tillage, changes
in the microbial activity and soil
quality could be anticipated. These
soil microorganisms have a strong
influence on the physical and chemical processes in soil. They bind soil
particles into aggregates, which in
It is widely known that continued
conventional tillage operations
have a profound negative impact on soil quality. Even with
enough residues on the soil surface, soil disturbance will still
have a negative effect on soil
quality, which is not easily rectified. Soil is a living biological system and the practice of tillage
have adverse effects on soil life.
It is important to minimise soil disturbance by tillage to less than
30% of the soil surface area. Reduced tillage is one of the three
principles which forms the basis
of conservation agriculture.