By Roelof Bezuidenhout
With the current focus on regenerative farming, we seem to have forgotten about an old threat: soil erosion. In many ways, it’s the exact opposite of regeneration. While erosion is a natural process, mismanagement can cause soil built up over millions of years to be washed or blown away in a day, often irreversibly.
Back in the 1970s, the Department of Agriculture’s extension division took soil erosion seriously. It promoted the idea of resource conservation under the slogan “Farming in harmony with nature” – proof that the pursuit of sustainable agriculture is nothing new. At the time, the country’s topsoil was being washed away and blown into the sea, and dams silted up. The main causes were decades of overgrazing, ploughing marginal soils and poor cultivation practices.
To help stop the damage, the government introduced a law that prevented the subdivision of agricultural land into units smaller than the stipulated economic size for each region. Even then, the cost-price squeeze was already making it hard for farmers to earn a living. Many were forced to overexploit their natural resources simply to survive on farms that were too small to be economically viable.
The misguided assumption that soil and veld were infinite resources led to huge losses in topsoil, fertility and productivity. Earlier generations of farmers generally lacked a deeper understanding of how different components of the ecosystem interact.
The power of water and wind
The two main types of erosion that farmers should watch out for are gully erosion, where water carves deep channels in the land; and sheet erosion, where topsoil is removed in a thin layer. Sheet erosion, caused by both water and wind, is particularly common on flat terrain that has been stripped of vegetation through grazing or cultivation.
If climate conditions worsen, we can expect more frequent and severe dust storms in dryland farming areas – just as degradation will worsen on overgrazed veld.
Research by the University of the Free State to quantify the degree of wind erosion on agricultural soils in the west-central Free State found the amount of dust collected between August and November was high compared to semi-arid regions of America. Interestingly, the most erosive period was not during the driest time of year (August to early September), but rather the very windy stretch from late September to November – despite soil moisture from the spring rains in October. The problem is a short spell of extreme wind can cause far more erosion than a few days of moderate breeze.
Preventative measures
Identify and stabilise vulnerable areas of land that are at risk or already showing signs of erosion.
The amount of soil loss is directly related to the extent of ground cover. Vegetation slows the flow of water and reduces wind speed at the surface. Unfortunately, re-establishing plant cover is a slow and sometimes impossible process. This is why prevention is far more effective than cure.
When you plough ridge-and-furrow patterns perpendicular to the dominant wind direction, the roughened surface offers greater aerodynamic resistance, helping to reduce erosion. The rougher the surface, the more friction it generates, and the better it disrupts wind flow.
This protective effect only works, however, when wind hits the ridges at a right angle. If the wind shifts and blows parallel to the ridges, the benefit is reduced or lost entirely. Unfortunately, wind direction often shifts in late winter and spring. A farmer who ploughs to counteract the prevailing north-westerlies may find the field exposed when the westerlies take over, and vice versa. In short, you cannot win on all fronts unless you’re willing to plough weekly, which is, of course, impractical.
Combating erosion is costly, but any action that slows water runoff or reduces wind speed at the soil surface will help preserve topsoil.
 | Roelof Bezuidenhout is a fourth-generation wool, mohair, mutton and game farmer and freelance journalist. Attended Free State University, majoring in animal husbandry and pasture science. Other interests include agricultural extension and rural development. |
