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Januarie 2018
14
ON FARM LEVEL
Conservation agriculture
CA proofs to be key in sustainability
2: Dry clods sealed with wax and ready to be im-
mersed in water to determine their volume via meas-
urement of the displaced water.
3a and 3b: The zero-fertiliser strip (3a) with chlorotic
plants can clearly be seen and (3b) plants in the zero
fertiliser strip without any adverse leaf symptoms but
they became tasselled a little later.
2
3a
3b
Photo 3a shows the crop chlorosis shortly
after emergence in a plot receiving no fer-
tiliser, because of a decreased amount of
chlorophyll in the leaves, often as a result of
nutrient deficiency. However, the yellowing
on these plots disappeared soon after with
the only lasting effect delayed flowering
(see
Photo 3b
).
The following could be the reasons why the
initial chlorosis was observed:
Roots only reached residual nutrients
after a while.
An N-negative period.
An initial period of dry soils until the
point where 70 mm of rain fell.
Whatever the case may be,
Graph 3
on page
13 shows how little the yields varied over
different fertiliser levels ranging from zero
fertilisation to 617 kg/ha of a 3:2:1(25) mix-
ture. The plot without fertiliser was even-
tually not hampered in terms of grain
production.
The highest nitrogen (N) level applied was
77 kg/ha (N), which is relatively low. The last
value in Graph 3 (8 t/ha) depicts the yield of
a control treatment representing the normal
farm fertilisation practice where a total of
120 kg/ha N was applied. No yield difference
was observed between this treatment and
treatment with no fertilisers.
The findings of this fertiliser trial were gen-
erally confirmed by another fertiliser trial
in the study area for which results are not
presented here. The second trial was done
with only variable N levels. The plant popu-
lations of these trials were 45 000 plants/ha.
According to the plant population trial an
upper yield limit of approximately 8 t/ha
had been set. Due to this fact increased
fertiliser levels could not increase yields
beyond this point. It is extremely significant
that the yield limit could be reached without
added fertiliser.
Conclusions
Results from the Ascent (Vrede) CA trials
for the 2016/2017 season presented in this
article, showed a range of positive impacts
on soil health, soil compaction, rainfall use
efficiency, reduced need for fertiliser and
sustained high yields.
Under the current difficult economic situ-
ation for grain producers and major en-
vironmental threats, such as soil erosion
and climate change, CA would have a sig-
nificant positive effect on the sustainability
and profitability of crop production systems
in the Vrede area if it is to be scaled out to
many more producers.