Mr Rennie, of Fife, spoke at the oat industry field day near Gore last week.
He hoped people appreciated how much work went into the oat trials in Southland, led by Plant Research New Zealand, supported by the New Zealand Oat Industry Group.
The trial sites in Southland were more impressive than any oat trial site in the United Kingdom, he said.
He grew New Zealand oat variety L5 in a trial plot on his farm, alongside eight British oat varieties, and said L5 came out on top.
However, it was difficult to get a new New Zealand variety registered to grow in the United Kingdom.
The oat harvest in the UK last year was the second-worst on record.
A wet spring delayed the sowing of oats by a month, he said.
"We waited and waited and waited."
Every season was different, he said.
"Whatever happened last year, forget it because next year will be totally different."
