A former MSc student in agronomy at Stellenbosch University (SU), Ruan van der Nest, is a co-recipient of the prestigious Junior Captain Scott Memorial Medal this year. It is awarded annually to the best MSc student at a local university by the South African Academy for Science and Arts. This year students in botanical science were eligible.

Entries received were of such a high standard that the Academy decided to make two awards rather than one, as is the norm. Van der Nest's co-recipient is Wilku Meyer of the University of the Free State.

Van der Nest completed his MSc Agric studies in 2020 at SU under the supervision of Dr Pieter Swanepoel of the SU Department of Agronomy, Dr Johan Labuschagne of the Western Cape Department of Agriculture, and Dr Ailsa Hardie of the SU Department of Soil Science. The research for his thesis, titled Liming strategies for barley and canola production in no-tillage systems was done on about 150 farms across the Swartland and southern Cape.

Study supervisor Dr Swanepoel is overjoyed at the success of his student and says: “He has always had the ability to work independently and perform a scientific experiment of excellent quality. The fact that he published an article in a highly rated international journal before he had submitted his MSc thesis testifies to this and was an additional motivation for awarding the MSc degree to him cum laude.

“His research has made an important contribution to new knowledge regarding the reaction of these two crops to liming practices in the Western Cape," says Swanepoel.

Van der Nest collected soil samples in the Southern Cape and Swartland to determine the scope and geographical distribution of soil acidity and stratification. The soil samples which he collected at various sites which had not been tilled for many years, showed that especially the Swartland has relatively acidic soil.

About 20% of soil samples from the Swartland had a pH level of less than 5.0, which is suboptimal for the cultivation of wheat, barley and canola. Especially soil at a depth of 5 to 15 cm tended to be acidic. “This can be ascribed to the slow movement and reaction of lime within the soil," says Van der Nest.

In a field trial he investigated the form, fineness and purity of lime. In addition, he looked at the difference which incorporation of different grades of lime made to the chemical attributes of soil, and how it influenced the growth and development of barley and canola.

He found that both crops did not really show a reaction to the addition of lime within the first two years. Micro-fine granulated lime which was applied at the recommended level showed faster movement in the soil than standard Class A lime and managed to neutralise soil acid levels faster without disturbing the soil. Soil disturbance through tillage, which is often not advisable on conservation agriculture farms, was however still the most effective way of neutralising soil pH at various depths.

“Micro-fine granulated lime is much more expensive that ordinary Class A lime, and farmers will have to decide for themselves whether the high input costs are justified," is Van der Nest's opinion.

Lime which was introduced with various soil tillage actions led to slightly improved plant growth and development in both barley and canola.

“This more optimal growth is most probably the result of additional soil advantages from the ploughing action, such as preventing compacting of soil. It also causes a decrease in nutrient stratification and the nutrient uptake which is made gradually available to plants from soil organic material."

Van der Nest, who grew up in Pretoria and was head boy of Cornwall Hill College, says he originally chose agronomy as field of study due to his interest in and love of nature and outdoor life.

“As my knowledge of soil, various crops and agricultural systems increased, my interest grew," says Van der Nest, who incorporated undergraduate Soil Studies and Agronomy into his BSc Agric degree.

Currently he works in Zambia for Liseli Farms, and focuses on the cultivation of citrus, pecan nuts and various types of vegetables. 

​