NEWS
Conservation Agriculture and soil
fertility management: Part 1
Theoretical principles and practices
Hendrik Smith 1 and Gerrie Trytsman 2
Current Address: 1 Conservation Agriculture Facilitator and 2 Independent Scientist, Grain SA
Reprinted From: http://bit.ly/2XxvEIj
I
n South Africa, crop production sys-
tems based on intensive and continu-
ous soil tillage have led to excessively
high soil degradation rates with a re-
duction in natural soil fertility in areas
under grain production. It also results in
the consistent recommendation of the
use of huge quantities of chemical fer-
tilizers that are biologically unnecessary,
economically extravagant and ecologi-
cally damaging. Tillage results in the
oxidation and destruction of carbon
in the soil by increasing the soil oxy-
gen levels, thereby promoting bacteria
populations to expand and consume
active carbon in the soil. Soil organic
carbon (SOC), or soil organic matter
(SOM), is the key element that drives
soil health, which in turn is the primary
factor having an impact on sustainable
crop production. If sound farming prac-
tices are sustained over time, soil health
improvement could significantly esca-
late, influenced by positive changes in
a wide spectrum of soil parameters, in-
cluding soil fertility, which then result in
improved productivity and profitability
of farming systems.
There is general agreement among
key stakeholders in South Africa, that
soil health and sustainable crop-live-
stock production will only be achieved
through the adoption and implementa-
tion of Conservation Agriculture (CA)
principles and practices. CA is seen as
an ideal system for sustainable and cli-
mate-smart agricultural intensification
and regeneration, through which farm-
ers can attain higher levels of productiv-
ity and profitability, while improving soil
health and the environment.
One of the good agricultural practices
(GAPs) associated with CA is integrated
soil fertility management (ISFM), which
essentially depends on locally adapted
CA principles and practices to build-up
soil health, allowing producers to re-
duce the use of fertilisers, while sustain-
ing good and stable yields and increas-
ing profitability. This understanding is
Grassroots
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involved are transformations of carbon,
cycling of nutrients, maintenance of the
structure and fabric of the soil, and bio-
logical regulation of soil populations.
Ways to increase nutrient use efficien-
cy (NUE)
Nutrient use efficiency, which may be
defined as the yield obtained per unit
of available nutrients in the soil (sup-
plied by the soil + fertilisers), could be
improved as follows:
Figure 1: Crops can be planted into
crop residues without physically dis-
turbing the soil.
important if we wish to sustain produc-
tivity at the lowest possible costs, both
economic and ecological. Without be-
ing able to go into details, this paper
aims to provide a few principles, advan-
tages and examples of ISFM.
Integrated soil fertility management
This concept of ISFM emphasizes the
maximization of nutrient use efficiency,
the enhanced access of soil nutrients
to plant roots, the response of soil as a
living ecosystem and the role of sound
locally adapted soil management prac-
tices enhancing ecosystem functions
and services leading to improved soil
fertility. The concept acknowledges that
neither practices based solely on min-
eral fertilizers nor solely on soil ecosys-
tems services are enough for sustain-
able crop production, especially during
the transition years after starting with
CA on degraded soils. It also requires
well-adapted, disease- and pest-resist-
ant germplasm, as well as other GAPs.
The critical soil ecosystem processes
March 2019
• Adjustment of fertiliser application
rates based on (natural) soil fertility
levels taking account of SOC level,
organically bonded nutrients, nutri-
ent cycling and/or previous crop-
ping practices, especially legumes,
and their residue biomass.
• Apply fertiliser at the right time and
place and using the right source.
• Plant crops at the right planting
density having enough plants to
ensure optimal and efficient nutri-
ent access and yield. In CA higher
planting densities (around 30%
higher than the norm) or at least
above 22 000 p/ha ensures effective
use of soil nutrients and water in the
whole soil profile and surface area,
while reducing temperature at soil
surface level.
CA Principles and practices enhanc-
ing ISFM
Many producers world-wide have
achieved large improvements in soil
health in a relatively short time. What
are these farmers doing differently?
Minimum soil disturbance
Physical soil disturbance, such as tillage
with a plough, disk, or chisel plough,
that results in bare or compacted soil
is destructive and disruptive to soil mi-
crobes and creates a hostile, instead of
hospitable, place for them to live and
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