Continued on page 30
Q: How should we manage residues for better wind erosion
control on the sandy soils?
A: Of course, the more residues you leave on the soil surface, the better
(see
Photo 2
). The higher the maize stalks are cut above the soil surface,
the better for avoiding wind erosion. Standing stubble is more efficient
than laying stubble for wind erosion control. Planter technology has
improved drastically in order to plant in these conditions.
A knife-roller (roller-crimper) could also be used to flatten cover crops,
but the design and use of it should be correct, i.e. the blades should be
blunt and it should not be too heavy or too light. In a region with yields
of 7 ton/ha and a similar amount of crop residues, there should not be
any problem with erosion, provided that all the residues are left on the
soil surface.
Q: What about the use of different cultivars under CA?
A: Very little work has been done to develop cultivars specifically for CA,
but it is an issue to keep in mind and research should be encouraged on it.
Q: What is your experience with row-width and plant population,
e.g. using 0,5 m row width and higher plant populations, such as
in Argentina?
A: I would be cautious because plant population depends on rainfall. You
could increase the plant population a little bit. If your situation allows
higher plant populations with narrow rows, weed control will be much
easier, since your canopy cover will suppress weed growth.
(
Comment from Wynn Dedwith from Parys, Free State:
Have done trials
with 16 000, 20 000, 24 000 and 40 000 plant populations under 0,9 m and
0,5 m row width; under high populations the 0,5 m row width was doing
better, apparently because of better micro-climatological conditions in
the maize field. Varieties with single cobs and no suckers seem to do
better.)
Q: In sandy soil areas with low rainfall (around 450 mm per
annum) and high temperatures, soybean rotated with maize
leaves very little residues. How can we improve this situation?
A: In similar conditions in Brazil they have developed a crop rotation
system where they are seeding winter cover crops (such as black oats
or Brachiaria) by air before harvesting maize or soybean, to utilise the
residual soil water and nutrients and leave a thick, living mulch right
into the next planting season. There are other options to enrich the crop
rotation, since there are thousands of potential plant species to consider.
Crop diversity is the key and cover crop mixtures could be a real solution.
Q: What is the best way to integrate livestock?
A: If you want to improve the soil organic matter as quickly as possible,
it is better to keep animals out of the cropping fields completely by
separating the grazing system (e.g. under a long-term grass ley crop)
from the cropping system. This will stop the removal of crop residues by
animals. These two systems can be rotated after a number of years, e.g.
after five years. The ley crop will also help to recuperate the (degraded)
soil, preparing it for more productive cropping.
(
Comment from Wynn Dedwith from Parys, Free State:
By taking better
care of pastures for livestock, it is possible to keep animals out of crop
fields and retain residues.)
Q: Some producers in South Africa incorporate cover crops into
the soil using tillage. What is your view?
A: Incorporating cover crops using tillage implements is something from
the old, old books. In the olden days there was no other way of seeding
a crop than previously incorporating the cover crop with tillage. From
our experience in South America, we ask the question: Why should we
incorporate cover crops? On the soil surface the crops will mineralise
slowly (i.e. slow release of nutrients), compared to quick mineralisation
with tillage. My recommendation would be to leave the cover crops on the
soil surface, since it will be incorporated by nature through a biological
process (see
Photo 3
).
1. Improve your knowledge about the system, especially weed
control.
2. Analyse your soil (aim for a balanced nutrient status) and allevi-
ate soil acidity (liming).
3. Avoid soils with bad drainage.
4. Level the soil surface.
5. Eliminate soil compaction by cultivation.
6. Produce the highest amount possible of mulch cover.
7. Buy a no-till planter – only after steps 1 to 6 have been met.
8. Start on 10% of your farm.
9. Use crop rotation and green manure cover crops.
10. Be prepared to learn constantly and be up to date with new de-
velopments. Join the nearest CA study group.
Critical steps for a successful
CA adoption (Derpsch, 2008)
Photo 2: Maize is being seeded into wheat stubble. Red clay soil, Paraguay, 1990s.
Photo 3: No-till soybeans at the farm of Theodor Pankratz on very sandy soil
(± 80% sand) in Paraguay.
29
February 2014
