Optimal liming is key to preventing soil acidification

As much as 30% of South Africa’s agricultural soil resource is deemed to be acidifying, mostly due to inefficient or incorrect liming practices. This is according to a recent presentation by Dr Pieter Haumann, CEO of the Fertilizer Association of Southern Africa. Sabrina Dean reports.

- Sabrina Dean

The importance of liming to overall soil health is so widely recognised that financial institutions often require farmers to apply lime in order to qualify for production financing. Falcon equipment

South African farmers are aware of the need to prevent soil acidification and therefore lime their soil. But data obtained over nearly two decades has revealed that too little lime is being applied to reduce soil acidity.

According to Dr Pieter Haumann, CEO of the Fertilizer Association of Southern Africa, referring to a recent presentation given by Dr Kobus van Zyl, a senior agriculturist at Omnia, about soil acidity, data gathered over a period of 13 years from 2002 to 2015 showed that the median pH (KCl) of topsoil in the Free State had deteriorated by 0,7 to a pH of 4,23, with a similar pattern observed in North West.

The data showed that median acid saturation had increased 92% in the topsoil, while median subsoil acidity had decreased from 4,25 to 4,15, with sandy soils presenting the greater problem. The researchers found that median acid saturation had increased 39% in the subsoil over the study period.

Samples taken in 2018 showed the median pH of the subsoil had remained at 4,2, but median acid saturation in the topsoil had increased by another 13%.

Calcium loss in the subsoil since 2002 was measured at 15%, while magnesium loss was 20%.

Fast Facts

•  Particle size is the most important physical property to consider when applying liming material.

•  Australian farmers are regarded as the leaders in most aspects of combating soil acidity. Much of the research done in Australia is also applicable in south Africa.