FEATURE
improve the soil structure and break
compacted layers and hard pans. The
cover crops also permit a rotation in
a monoculture and can be used to
control weeds and pests.
Cover crops are grown during fallow
periods, between harvest and planting
of commercial crops, utilizing the
residual soil moisture. Their growth is
interrupted either before the next crop
is sown, or after sowing the next crop,
but before competition between the
two crops starts. Cover crops energize
crop production, but they also present
some challenges.
The presence of a mulch layer (of
dead vegetation) in conservation
agriculture inhibits the evaporation of
soil moisture, yet leads to greater water
infiltration into the soil profile. The
percentage of rainwater that infiltrates
the soil depends on the amount of soil
cover provided.
As different cover crops produce
different amount of biomass, the
density of the residues varies with
different crops and thus the ability to
increase water infiltration.
Cover crops are useful for protecting
the soil, when it does not have a
crop. They also act as an additional
source of organic matter to improve
soil structure. While recycling nutrients
such as potassium and phosphorus,
these crops make the nutrients readily
available to the crops that follow. Vegetative cover is important in CA
for the protection of the soil against
the impacts of raindrops; to keep the
soil shaded; and maintain the highest
possible moisture content. We have
seen their importance for nutrient
recycling; but they also have a physical
and perhaps allopathic effect on weeds
such that they reduce their incidence
leading to a reduction in agrochemical use.
Different plants, with diverse rooting
systems, explore different soil depths
within the profile. They may also have
the ability to absorb different quantities of
nutrients and produce distinct root exudates
(organic acids) resulting in benefits both for
the soil and for the organisms. Species diversification
Crop rotation
The rotation of crops is not only
necessary to offer a diverse “diet” to
the soil micro organisms, but as they
root at different soil depths, they are
capable of exploring different soil layers
38 |November - December 2018
for nutrients. Nutrients that have been
leached to deeper layers and that are
no longer available for the commercial
crop, can be “recycled” by the crops
in rotation. This way the rotation crops
function as biological pumps.
Furthermore, a diversity of crops in
rotation leads to a diverse soil flora and
fauna, as the roots excrete different
organic substances that attract
different types of bacteria and fungi,
which in turn, play an important role in
the transformation of these substances
into plant available nutrients. Crop
rotation also has an important
phytosanitary function as it prevents
the carry over of crop-specific pests
and diseases from one crop to the next
via crop residues.
Crop rotation results in a higher
diversity in plant production and thus
in human and livestock nutrition. It
also causes a reduction in risk of pest
and weed infestations. With crop
rotation there is a greater distribution of
channels created by diverse roots. This
then ensures better distribution of water
and nutrients through the soil profile.