Sugar cane was first planted in South Africa in 1848, and for most of the time since then was produced in a monocropping system. It was only in more recent years that agriculturalists and farmers began to understand the importance of biodiversity both above and below the soil surface.
As one sugar cane farmer, Dreyer Senekal, observes drily, “We used to have the view that if you needed to rotate your old sugar cane crop, you just planted a new sugar cane crop straight after it. The biggest change we might have made back then was to plant a different cane variety to the one we’d ploughed out.”
Senekal is the full-time agricultural manager of the Senekal Familie Boerdery (SFB), a diversified mega farming business established in 1978 by his father, Charl Senekal, who remains actively involved in the operations.
SFB’s agricultural enterprises cover 4 500ha of irrigated lands in Mkuze, northern KwaZulu-Natal, with water piped from Jozini Dam. The primary enterprise is sugar cane, but SFB also produces citrus, macadamia and chillies. In addition, Senekal has a small commercial beef herd that he runs as a hobby.
“Our access to irrigation and our warmer climate allows us to harvest our sugar cane every 12 months. Depending on the sugar cane variety, we get eight to 10 harvests before we plough out and replant. On average, we replant 400ha to 600ha annually on a rotational basis across our sugar cane operation. Our main varieties are N49 and N57, and we’ll soon be harvesting trials of newer varieties to see how they do. All of these varieties are specifically bred for production under irrigation,” says Senekal.
He adds that, for most of the year, the Mkuze area experiences high number of daytime heat units, about 7,5 hours of sunshine per day, an average annual temperature of 22,3°C, and a virtual absence of frost, all of which make conditions ideal for vigorous sugar cane growth.
However, irrigation is essential, given the average annual rainfall of only 550mm.
CLAY SOIL CHALLENGES
The two most common soil types in the area are Hutton and Shortlands. On the SFB farm, clay content averages a relatively high 35% to 40%, while in some parts of the farm this reaches as high as 70%. The main challenges with high-clay soils, especially in a sugar cane operation that uses heavy machinery, are surface capping and both surface and subsurface compaction.
A further challenge with SFB’s Hutton and Shortlands soils is that they tend towards an alkaline pH of 8 and above, as well as a build-up of exchangeable sodium in the deeper layers. This sodic environment exacerbates the dispersion of soil particles and the breakdown of soil aggregates, leading to compaction, run-off and erosion.
The sodium build-up became an even greater problem as drought conditions lowered Jozini Dam’s water level to 36% of capacity, thereby increasing the water’s concentration of natural sodium. However, the level of the dam is now at 56% and rising following recent rains, according to Senekal.
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