NEWS
Table 3: Salient analytical data for the degraded soil taken during the growing
season of a summer cover crop mix.
Soil pH (H 2 O)
7,3
Soluble Salts
mmho / cm
0,3
Excess lime rating
1
Soil Organic Matter (SOM), LOI %
0,8
Calcium ppm 187
Aluminium extractable ppm 651.6
% 4,6
ppm 378
Phosphorous Saturation
Iron extractable
Figure 3: A 100% cover by the mixed
summer cover crop residues.
Table 4: Critical plant nutrient levels in maize leaves.
Critical plant nutrients levels in leaf opposite and below the ear at tasseling
% of DM Ppm of DM N P K Mg Ca S Zn Fe Mn B
2.9 0.25 1.9 0.15 0.4 0.15 15 25 15 10
Source: Hoeft
& Peck, 1991
zal fungi. It has been shown in the past
that only 20% P fertiliser is taken up dur-
ing the first year after application, while
soil microbes provide plants with the
amounts of nutrients required. 12 kg of
K/ha - since there is sufficient amounts
of K in the soil, this application was just
to establish strong vigorous seedlings;
additional Sulphur and Zinc were also
applied. No further inputs as far as soil
fertility management were deemed
necessary. This was due to a great sup-
ply of nutrients in the cover crop resi-
dues that will be made available as the
CC biomass decomposes through mi-
crobial activity.
Photo 1 shows the soil surface before
cover crops was planted. Low levels of
cover with a soil surface crust and ero-
sion can be seen. The photo was taken
on 27 January 2016, just before the cov-
er crops were planted.
Figure 1: Soil with surface crusts and
signs of severe erosion. At the stage
when the cover crop was fully devel-
oped, photo 2 was taken on the 14
April 2016; the crop yielded an average
biomass production of 12t DM/ha.
soil ecosystem functions and decrease
the rehabilitation or transformation pe-
riod to 3 or 4 years.
In a high temperature, low rainfall en-
vironment such as Ottosdal, the high
amounts of CC residue would almost
immediately have had a positive effect
on the soil water content with much
higher infiltration rates and much less
water loss through evaporation. During
the following few years, the presence of
a diversity of plant roots in the soil will
most probably have a positive impact
on soil microbial diversity and activity,
including mycorrhizas, which are highly
dependent on a host and living roots.
These effects are currently being meas-
ured in on-going research in Grain SA’s
on-farm CA trials across the country.
The establishment of perennial pastures
is another possible solution, as part of
the crop diversity within integrated
crop-livestock systems, to facilitate the
Grassroots
Vol 19
No 1
Figure 2: Fully developed mixed sum-
mer cover crop system.
restoration process. From a degraded
soil to commercial maize production
In order to put this field back into maize
production (as was aimed for), the fol-
lowing fertilizer application rates (side
dress) were used to establish the maize
crop aiming for a 5 t/ha yield in the
2016/2017 season: 33 kg of N/ha – this
amount of N will cover a yield target of
only 2 ton/ha; the remaining N required
will be provided through nutrient cy-
cling and C decomposition of the CC
mix’s DM and roots. Depending on the
production of the CC, a saving of 70-80
kg/ha of N can quite easily be attained
during the first year (see Table 1, Part 1).
Eighteen kg of P/ha – this amount of P
will cover a yield target of 5 ton/ha; from
the Haney soil analysis it is clear that C
content and microbial biomass activity
is not yet sufficiently restored to recycle
and/or release sufficient soil P to sup-
port plant P requirements for a yield tar-
get of 5 ton/ha. It is expected that more
P will be released from the soil in the
next couple of years through biological
processes and colonization of mycorrhi-
March 2019
Photo 3 shows the CC residues (left
standing) killed by the winter frost,
taken on 2 September 2016. A decision
was made not to flatten it because of
the positive effect the standing residues
would have had on wind and water ero-
sion. The cooler soil under the residue
cover will also benefit the water cycle
due to the lower evaporation from the
soil surface.
Photo 4 was taken just before the maize
was planted on 12 December 2016; note
Figure 4: Field with summer cover crop
residues just before planting the maize
crop.
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