Maize, which is a monocotyledonous plant, has long been grown successfully in East Griqualand for grain and silage production. However, farmers in the area have been limited in their options for profitable dicotyledonous summer crops that they can grow in rotation with their maize.
This is primarily because East Griqualand, which straddles the border between KwaZulu-Natal and the Eastern Cape, has milder summers, with fewer heat units, than much of the rest of South Africa’s grain production areas.
However, due to developments in breeding, sunflower is showing promise for this particular purpose, according to Corné van der Westhuizen, Pannar Seed’s marketing agronomist in North West.
“In the north-west regions of South Africa, where sunflower is common, production is usually planned around a farm’s primary maize grain crops. For this reason, the yield and quality of sunflower harvests there are generally below full potential,” says Van der Westhuizen.
Sunflower production planning, he adds, should incorporate field selection, hybrid selection, fertilisation planning linked to a realistic yield target, and selection of an appropriate planting date and plant density.
The first aspect of field selection is to analyse the land’s production history. This should include the following:
The crops that were grown previously on the land;
The herbicides and other measures that were applied to manage weeds in these crops (with particular note taken of any atrazine-based products);
The weed species that were difficult to control using conventional actions;
Projecting the weed species that could be a threat in the coming summer season, and deciding how these should be managed.
“Farmers should recall which broadleaf herbicides were used in growing previous crops and whether any of these have residual effects that can negatively affect a following sunflower crop,” says Van der Westhuizen.
It should also be kept in mind that this crop is adversely affected by a soil pH of below 4,8 and by soil acid saturation of more than 10%. These can result in molybdenum deficiency and aluminium toxicity in the soil.
While liming can be used to counter soil acidity, it can also cause the residual molecules of recently used herbicides bound to the clay particles of the soil to be released, damaging the subsequent sunflower crop.
According to Van der Westhuizen, a sunflower plant requires substantial volumes of nutrients to achieve optimal yield, and its taproot system can source nutrients and moisture from deeper in the soil profile than the fibrous root system of the maize plant.
Nitrogen is the primary yield-limiting element in sunflower production. A low level of plant-available potassium in the soil can also be a problem. Only a small percentage of the total potassium uptake is removed from the land with the grain, yet more of this element is taken up from the soil than any other.
To make matters even more complex, an excess or deficiency of one element can have a positive or negative effect on another. An excess of nitrogen, for example, can negatively influence the uptake of potassium.
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