Conservation agriculture
Inputs/Production
Januarie 2014
32
It is important to have proper crop rotations and cover crops in place.
You need to have residue covering the soil, otherwise raindrops will
“dynamite” the soil. I agree on the consideration of tine-planters during
the transition years. (Some producers in the audience mention that they
have been using discs from the start.)
Q: Should we use controlled traffic or change the planting
direction every year (e.g. 30˚)?
A: Both are acceptable and any traffic control system is good, where it is
possible to introduce it. If it is difficult to do controlled traffic, the most
important is to reduce the traffic in the crop fields and to use cover crops
and rotations. Use low pressure tyres (0,6 bars); do not use too heavy
equipment. I prefer a number of smaller tractors compared to one big
tractor.
Q: What about contour banks in CA fields?
A: In Brazil contours were subsidised and afterwards some CA producers
decided to remove them. It is wrong to remove them; if you remove, do
not remove all of them, maybe some. Some situations might occur where
you have too little cover and contours will be needed. Keep around 50%
contours and consider using broad-based contours on which you can
plant or drive over. The planter should be flexible enough to work under
uneven soil conditions.
Q: What is the most efficient way to improve soil organic
matter (SOM)?
A: Produce as much biomass as possible for your location. Fertilise crops
well and use the right varieties. Try to use cover crops – cover crops
have been developed for any situation, e.g. as catch crop, intercrop,
fodder crops, green manure, etc. Consider African grasses to improve
underground biomass (i.e. root mass).
Q: What about soil pH and liming in CA?
A: Soil acidity should be assessed and corrected (i.e. lime incorporated
into the soil) before starting with CA. Afterwards, apply lime on the
soil surface. Organic acids of some plants, especially cover crops (and
also root exudates) move lime into the soil profile; it is not necessary to
incorporate the lime. Apply 1 ton/ha/year to increase pH slowly and not
3 ton/ha every three years. Phosphorous (P) concentrates on the soil
surface, but roots in the CA system will reach P in the surface soil layer.
Q: What about cattle on CA fields – are there long-term trials
showing yield/economic differences?
A: Trials have been done in Brazil. In the beginning they have noticed soil
compaction, but after producing enough soil cover, it was sustainable.
Cattle’s hoofs must not tread on soil too much; reduce periods of
cattle grazing on the fields to the minimum (i.e. a few weeks per year).
Remember, soil cover is the most important thing in CA.
Q: What kind/type of cover crops can be used?
A: There are many types and options for different situations or problems.
Researchers and/or producers need to identify problems and possible
cover crops with the potential to alleviate these problems. Some
screening trials will probably be needed at the beginning to identify
the most suitable cover crops; thereafter they should be integrated into
the cropping systems.
An example is the sowing of temperate crops (e.g. oats, vetch and radish)
into maize or soya fields just before harvest, to use residual soil water
and nutrients as a “catch crop” through the winter – could also serve as
standing fodder and to alleviate soil compaction. In this example, winter
cover crops soak up excess soil water and nutrients and supply food to
all the microbes in the soil during the winter months rather than microbes
having to use up SOM reserves for nutrients.
Microbes thrive under no-till conditions and winter cover crops. Cover
crop research is critical and local crops, e.g. indigenous legumes, should
be investigated and multiplied.
Figure 1: Root development
in conventional till (left) and
no-till (right). Research done
at IAPAR in Londrina, Brazil,
by Köpke and Vieira, 1983.
Conservation agriculture awareness
dialogues with Dr Rolf Derpsch
Continued from page 31
