The £900,000 investment was financed by the country's Rural Priorities fund, which aims to improve businesses' viability and competitiveness.
The new facility boasts energy efficient farm buildings for grading, processing and cold-storing potatoes and storing and drying grain. The buildings are 60 per cent self-sufficient, using renewable energy from two on-farm wind turbines, and also include a public room where visitors can learn about the farming environmental charity, Linking Environment and Farming.
Stevenson said: "This is a massive leap forward for my farming business, with a state-of-the-art fresh market potato store, plus grain storage, an environmental room for hosting the many visitors to the farm each year, and two wind turbines, plus on-farm environmental developments, including a mile of new mixed hedges.
"This scale of investment, totalling nearly £900,000, on a tenanted farm could not happen without support from this scheme; this is the first phase of an expansion of the Luffness Mains business and substantially improves the quality of our farm produce."
The store was designed by the Potato Council's Sutton Bridge crop storage research team and incorporates latest technologies for the storage of fresh potatoes for retail markets.
Lochhead said: "I'm delighted to be able to support this innovative development at Luffness Mains with Rural Priorities funding.
"Since its launch in 2008, Rural Priorities has approved grants worth a total of £378m for some 4,850 projects across Scotland. It continues to bring economic and environmental benefits to rural communities across the country."