He obtained his BSA (1938) and MSc (1941) from the University of Saskatchewan and his PhD from the University of Minnesota in 1952. From 1938-42 he was a research scientist at the Swift Current Research Station. Following service in the Royal Canadian Air Force (1942-45), he returned to Swift Current and from 1952-1976 was head of the forage production and utilization section at the Agricultural Canada Research Station. He had a one year leave of absence in Australia in 1960 doing a post-doctoral research assignment.

His background in growing up on a dryland farm led him in his research to seek drought resistant forage. Dave noted some alfalfa plants had creeping roots that made them better able to withstand drought and frost. He developed Rambler alfalfa with these characteristics. From Rambler he developed an improved variety called Rangelander that became widely grown across the Prairies and in North Dakota . Following Dave's retirement in 1976 forage crop breeders developed a new creeping rooted alfalfa which they named Heinrichs in his honour.

During his career he travelled extensively throughout Saskatchewan advising farmers and ranchers on pasture mixes. His repeated recommendation was a mixture of crested wheat grass and alfalfa for spring pasture, brome or intermediate wheat grass and alfalfa for summer and Russian wild rye and alfalfa for fall. Community pastures and co-operative pastures across the southwest followed his advice.

His accomplishments won him wide recognition. Across North America he was considered a leading authority on alfalfa. In 1968 he was named a Fellow of the Agricultural Institute of Canada. The same year he was made an honorary life member of the Canadian Seed Growers Association. In 1977 he was named the Canadian Seed Trade Association Man of the Year. In 1986 he became an honorary life member in the North American Alfalfa Improvement Conference, an organization he had headed in 1970-72.

David was active in the Swift Current community. In 1958 he was selected from the district to become a member of the University of Saskatchewan Senate . He served as a Swift Current alderman and chairman of the works committee for nine years. In retirement he became a successful landscape painter. He died in 1999.