Q: We have the experience that no-till disc planters do not
penetrate into clay soils. When are tine or disc planters
appropriate?
A: This discussion has been going on in South America for many years.
Herbert Bartz (pioneer CA producer in Brazil) has been doing CA with
discs under high clay soils very successfully.
My opinion is that tine planters would be appropriate during a transitional
phase, where you are starting CA with soil organic matter levels of 0,2%,
for example. But if you want to go to the top of the system and quickly
accumulate soil organic matter you must switch to discs. When you are
using tines, especially in narrow row spacing, you are actually ‘tilling’
the soil.
(
Comment from Cobus van Coller from Viljoenskroon, Free State:
We
usually have compaction in the first 10 cm - 15 cm in degraded sandy
soils; we use a small tine (12 mm - 13 mm wide) on the no-till planter,
which we believe will probably work better for the first seven to ten
years while we have the compaction, whereafter a disc planter could be
introduced.)
Q: How do you apply fertilisers under CA?
A: There are different schools of thought. Some say you can fertilise
in the row for a period, whereafter you can broadcast and your crops
will respond well. Others say you don’t have to fertilise soybeans, since
it responds very well to residual fertiliser of the previous crop, usually
maize.
So, if you have large areas of land to plant, your operation will be much
quicker if you don’t have to fertilise, i.e. if you don’t fertilise soybean and
apply all your fertiliser to the maize. Another system that is used is to
heavily fertilise the cover crop, flattening it down and these residues and
roots will return (recycle) the soil nutrients making them available to the
next crop (see
Photo 4
).
Q: Why do you want to flatten the cover crops mechanically?
A: First of all, we would like to keep the chemical use as low as possible. I
would like to remind you that glyphosate is not so benign, since it causes
problems in the long run and I am concerned that we are relying too
much on only one herbicide. So whenever we have the opportunity to
avoid glyphosate, I would prefer to use this alternative.
I am not against glyphosate; if it disappears from the market, CA will have
a huge problem. However, we have to diversify our herbicide programme
and when you rotate crops you are forced to rotate herbicides. If you
are doing monoculture with GM crops, you are constantly increasing
your dependence on glyphosate (see
Photo 5
).
Q: Is it better to control weeds within a matured maize stand
(and use glyphosate again)?
A: I would prefer to use a inter row spraying (e.g. with gramoxone and
180° nozzles at the latest stage you can drive in with your tractor) to avoid
harvesting with weeds and the reseeding of weeds. If the weeds produce
seeds, they cannot serve as a “cover crop”; if they do not produce seeds
they can, but biomass production from weeds is generally quite low.
The presentations and dialogue with Dr Derpsch clearly illustrated
the range of benefits resulting from CA, pressing the urgent need for
producers to adopt the system, especially in South African conditions
that are prone to soil degradation and droughts.
Responses from participants who attended these two events were very
positive, sparking new momentum to the much needed thrust to promote
CA among grain producers in South Africa.
Photo 4: Sunflowers seeded in no-till in Paraguay, December 2001.
Photo 5: No-till soybeans at the Parex farm in Paraguay with red clay soil.
Conservation agriculture awareness dialogues
with Dr Rolf Derpsch
Continued from page 29
Conservation agriculture
Inputs/Production
Februarie 2014
30
