Oktober 2013
84
Focus on livestock
How to use cover crops
to your advantage
DEAN MILLER, GROUP MARKETING, ADVANCE SEED
The world population currently stands at
approximately 7 billion people, and will
increase significantly in the next decade or
two. This means that our natural resources will
be placed under increasing pressure to provide
for the masses at large.
One of these natural resources is the available
arable agricultural land to provide an ever
increasing supply of food to feed this growing
population.
It may not come as a surprise to most that
7 billion people get their sustenance from the
20 cm of topsoil that has been provided for by
Mother Nature. It is therefore imperative that
this natural resource is cared for now more so
than ever before.
Cover cropping can provide one of the means
of caring for our arable land. Cover cropping is
an old, sustainable, good agricultural practice
which has been used for centuries, but in
recent times has been largely forgotten as a
technique. Today, cover cropping is growing
in its use in small scale as well as commercial
agriculture, as soils across the globe become
depleted through less than optimum
management techniques.
A cover crop is a crop planted primarily to
manage soil fertility, soil quality, water, weeds,
pests, diseases, biodiversity and wildlife in
an agro-ecosystem. This ecological system
is managed and shaped largely by humans
across a range of intensities to produce food,
feed and fibre.
Producers choose to grow and manage
specific cover crop types based on their own
needs and goals, influenced by the biological,
social, cultural and economic factors of the
food system in which farmers operate.
Soil fertility management
One of the primary uses of cover crops is to
increase soil fertility. These types of cover
crops are known as “green manure”. They are
used to manage a range of soil macro- and
micro-nutrients, as well as to stimulate the
living microbial biomass, which is all important
when trying to increase soil fertility and soil
productivity. The primary intention of cover
cropping is to provide food for the unseen
microbes working for us in the soil.
Green manure crops are commonly
leguminous. They are high in nitrogen, which is
fixed in nodules from the available atmospheric
N, by differing strains of
Rhizobium
spp.
bacteria and can often provide some of
the required quantity of nitrogen for crop
production. Green manure crops are grown
for a specific period and then ploughed under
or left on the soil surface as a mulch, before
reaching full maturity in order to improve soil
fertility and quality.
Legumes have the unique ability to convert
biologically unavailable atmospheric nitrogen
gas (N
2
) to plant available nitrates (NO³)
through the processes of immobilisation
and mineralisation in conjunction with the
Rhizobium strains of soil bacteria.
Cover crops can also be used as “catch crops”
which are used to retain and recycle soil
nitrogen as well as the other macro-nutrients
and micro-nutrients already present in the soil
profile. The catch crop in this case takes up
residual nitrogen remaining from fertilisation
of the previous crop, as well as all other
nutrients necessary for plant growth. This
prevents loss of nitrogen through leaching,
gaseous denitrification or volatilisation.
The nitrogen tied up in the catch crop biomass
is released back into the soil once the catch
crop is managed, and begins to be digested by
the soil microbes.
Soil quality management
Cover crops can also improve soil quality
by increasing soil organic matter levels.
Increased soil organic matter enhances
soil structure as well as the water and
nutrient holding and buffering capacity of
soil.
Cover crops can performmultiple functions
in an agro ecosystem simultaneously.
However, they can be grown for the sole
purpose of preventing soil erosion.
Soil quality is managed to provide optimum
conditions for crops to flourish, and can
be defined as: Soil quality is the capacity
of a specific kind of soil to function,
within natural or managed ecosystem
boundaries, to sustain plant and animal
productivity, maintain or enhance water
and air quality, and support human health
and habitation.
Water management
Cover crop biomass, which is mulched onto the
soil surface, acts as a physical barrier between
rainfall and the soil surface, allowing raindrops
to steadily trickle down through the soil profile.
Cover crop root growth results in the formation
of soil canals (pores) which in addition to
enhancing soil macro fauna habitat, provides
pathways for water to filter into the soil profile
rather than draining off the field as surface flow.
Cover crops can be used as mulch to conserve
water by shading and cooling the soil surface
and by creating a micro-climate between
the top of the soil and the bottom of the mulch
layer, especially in regions where water for
crop production is in short supply.
Weed management
A thick cover crop stand often competes well
with weeds and will prevent most germinated
weed seeds from completing their life cycle
and reproducing. Cover crops left on the soil
surface drastically reduce light transmittance
to weed seeds and therefore reduce weed seed
germination rates.
Certain cover crops are known to suppress
weeds through allelopathy. Allelopathy refers
to the beneficial or harmful effects of one plant
on another plant, both crop and weed species,
by the release of chemicals from plant parts by
leaching, root exudation, volatilisation, residue
decomposition and other processes in both
natural and agricultural systems.
Product information
