The Holy Grail for wheat yields in the 1970s was to grow a 10-tonne per ha crop – now 20-tonne is the target and a Scottish crop has hit 15.5 tonne per ha this past week.

Former wheat world record holder, Gordon Rennie, from Stenton, St Andrews, was astonished when his crop of LG Scyscraper last week hit spot yields of 18 tonnes per ha (before drying). Wet, the 13 ha field averaged 15.5 tonnes at 23% moisture content and dry it levelled at 13.6 t/ha.

He told The SF: "Whilst these are unofficial figures, I am confident these yields have beaten all expectations and are down to soil health and good nutrition. We still use the Schleswig-Holstein system that produced the world record yield in 1981 when we grew 13.99 t/ha.

"In 1979, we adopted that German system of growing wheat. The result was fantastic and we grew the very first 10-t/ha crop with a German variety called Kanzler.

"Now, the Holy Grail is to grow a 20-tonne crop. Hence, why the Foundation of Arable Research (FAR) NZ set up the 20/20 club, with the ambition of achieving that goal. Earlier this year, I met the new Scottish director of FAR, Alison Stewart. She told me that until we had better genetics, the maximum achievable yield was 18 tonnes per ha," said Mr Rennie.

"So, I was fascinated to sit in the jump seat of our New Holland combine as we harvested our first field of wheat last week. This was a 13 ha field of LG Skyscraper. It was sown early, in good conditions after a very good crop of spring oats. As I looked at the yield meter, there was an OMG moment, as the best part of the field hit 18 tonnes per ha.

"In a 'normal' crop of wheat, the combine sits happily between 4-5 km per hour. In this monster crop, we had to slow down to 2 km per hour. Where did this huge yield come from? The secret of high yields is to have the highest number of plump grains per ear of wheat and to sow high vigour seed into a very good seedbed."

Mr Rennie added: "Variety choice is essential. LG Skyscraper, for example, is an excellent choice – in contrast, varieties with ear sterility problems, such as KWS Extase, would be a poor choice, in my opinion."