Conservation agriculture
Inputs/Production
Februarie 2014
28
Conservation agriculture
awareness dialogues with
Dr Rolf Derpsch
DR HENDRIK SMITH, CONSERVATION AGRICULTURE FACILITATOR, GRAIN SA
For two days in August last year, Grain SA’s Conservation Agriculture (CA)
programme entertained a number of participants through two awareness
events with Dr Rolf Derpsch as presenter. On the 14th the event was held
in Pretoria for Limpopo, Mpumalanga and Gauteng and on the 15th at
NAMPO Park in Bothaville for the Free State and North West Province.
The information and lessons learned during these events are seen
as critical to improve practices of existing CA producers, but also to
spark the interest and knowledge of producers interested to start CA.
In more detail the dialogue with Dr Derpsch during the second event is
highlighted below.
Q: Is it necessary to till (rip) the soil under CA at some stage?
A: Any disturbance of the soil after you have started CA will bring you
back to the start and you will not reap the full benefit of the system. If you
apply the three principles of CA correctly, there will be no need to rip the
soil at any stage. When crops such as peanuts are used in CA, the soil will
be disturbed when these crops are harvested. A partial solution to this
problem is to cover the soil, preferably with cover crops, as quickly as
possible after harvest.
Q: How should we treat very sandy soils (less than 5% clay) with
very low soil organic matter in dry areas under CA?
A: These types of soils are also found in other areas, for example in
Paraguay, which has been degraded by tillage and have soil organic
matter levels of around 0,2%. This is the worst situation to start CA
that you can think of. However, even in these situations CA is the better
solution to recuperate degraded soils and farm sustainably (see
Photo 1
).
In these severely degraded sandy soils probably the best alternative
is to establish a long-term grass ley cropping system for around five
years using African grasses for example. Otherwise annual cover crops
with a high below- and above-ground biomass, such as Sunhemp
(
Crotalaria juncea
) or Pearl millet/Babala (
Pennisetum glaucum
) should
be incorporated into the cropping rotation.
You will have to invest something to improve the condition, which
is ultimately leading to higher soil organic matter. So you will have
to find out which are the crops that will give you the best results in
these conditions, i.e. the highest amount of biomass in the shortest
possible period.
Q: Do you think we will run into disease problems under CA,
especially soil-borne diseases?
A: Entomologists and pathologist are always concerned about this
issue, warning that it will cause a collapse of the whole cropping system.
Fortunately nature is a little bit wiser than us, because predators or other
beneficial organisms, which could not survive under conventional tillage,
will also increase under improved conditions (under CA).
Under higher soil organic matter and crop diversity levels, the soil is much
more resilient. Aphids, for example, do not like residues. Some pests will
decrease, others will increase, but eventually you will have a balance.
Q: Isn’t root density more important than soil cover?
A: It is certainly an under-emphasised factor. It is always a good idea to
increase the diversity, amount and quality of (living) roots in the soil, such
as using African grasses.
Part 2: Bothaville, 15 August 2013
Photo 1: No-till soybeans at the farm of Theodor Pankratz on very sandy soil (± 80% sand) in Paraguay.
Dr Rolf Derpsch
