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13
January 2018
In the absence of penetrometers that can
measure compaction in a direct way, root-
ing patterns and bulk densities were conse-
quently investigated.
CA and soil compaction
Photo 1a
and
Photo 1b
shows a soil profile
with rooting characteristics in a maize field
that has been no-tilled for five years. Soy-
beans were grown the previous summer
and a winter mixed cover crop preceded the
maize.
A concentration of roots is seen directly
under the plant row (Photo 1a). This is co-
incidentally where the previous year’s soy-
bean row was situated. A second concen-
tration of roots was observed in the middle
between rows where the winter cover crop
row had previously been (Photo 1b).
These observations could suggest that old
root channels were used by the maize roots
to reach and fully exploit the effective root-
ing depth. Soil bulk density measurements
confirmed that the soil porosity would
have been supportive for easy root growth.
These measurements in fact, suggested
that soil porosity was improved by the CA
practices followed on this farm.
Bulk density was determined at a depth of
30 cm comparing measurements of the no-
till soil with a tilled soil of a neighbouring
farm. The clod and wax method was used
(
Photo 2
on page 14) on clods that were
sampled under the tractor wheel tracks
where compaction was supposed to be the
greatest.
Bulk densities were 1,3 g/cm
3
and 1,6 g/cm
3
for no-till and tilled soils respectively. This
indicates that the no-till soil is more porous
and less compacted and defies the con-
ventional wisdom that tillage to a depth of
45 cm is needed to alleviate the compaction
in this area.
On the contrary, tillage destroys soil struc-
ture and root channels leading to compac-
tion, lower infiltra-tion rates and less soil
water. Micro-organisms that are necessary
for enhancing and preserving soil structure,
porosity and aeration, are also disrupted,
sustaining the destructive spiral of tillage
practices.
CA and plant density
A plant population trial on the farm indi-
cated that yield potential had increased be-
yond the point where the traditional norm of
40 000 plants/ha could utilise the season’s
full potential. It should be noted that total
rainfall was below normal at approximately
580 mm.
In this light, the current year’s high yields
were very satisfactory reaching record
yields in some cases.
Graph 2
shows that
yields of a little less than 8 t/ha were pos-
sible with approximately 40 000 plants/ha.
It can be assumed that the potential was
even higher (9 t/ha) under higher plant
populations.
This farm’s practice is to use 45 000 plants/
ha, which is already higher than the norm
for the area, but probably not high enough
to match the higher potential under CA
systems.
The following factors generally contribute
to an increased yield potential under CA:
Improved soil physical properties;
more effective utilisation of rainfall and
sun energy;
improved soil cover, higher soil micro-
bial activity; and
more favourable microclimate above
the soil surface in the field crops.
CA and soil fertility
Results of a fertilisation experiment at
Skulpspruit supported the notion that CA
practices improve soil health and soil fer-
tility to a level where higher yields are ob-
tained with lower fertiliser application. This
fertiliser experiment was planted with diffe-
rent levels of a 3:2:1(25) fertiliser mixture.
Graph 1: Soil water content for different tillage treatments prior to and after the summer rains began
to fall in October 2016.
Graph 2: Plant population/yield curve for maize.
Graph 3: Effect of fertilisation levels on maize yield produced under CA conditions.