Jacobus Stephanus Marais, agronomist, grew up in Pretoria but matriculated at Stellenbosch. Continuing his studies at Victoria College (from 1918 the University of Stellenbosch) he was awarded the BA (Honours) degree. He also received a bursary to study overseas and did so at the University of Illinois in the United States, where he received his doctoral degree in agricultural chemistry in 1921 with a thesis entitled The comparative agricultural value of insoluble mineral phosphates of aluminium, iron and calcium.
Returning to South Africa in 1921 he was appointed as senior lecturer in agronomy at the University of Stellenbosch and promoted to professor of agronomy in 1930. In 1938 he was appointed in addition as head of the university's Stellenbosch-Elsenburg College of Agriculture, a position he held until his death. He was an agronomist of note and also an excellent administrator who's heart was in his work and who was always at the service of the university, its students, and the farming community. He did much to improve the agricultural soils of the Western Cape by promoting soil conservation, crop rotation and other sound agricultural practices. Over the years he published a number of articles in Farming in South Africa, including "Dry land lucerne in the winter-rainfall area" (1930, with C. J. Starke), "Kale: A succulent crop for the winter-rainfall area" 1930, with C. J. Starke), "Wheat varieties for the winter-rainfall area" (1931), "Soil fertility, wheat prices and the 1938 wheat crop" (1938) and "Development of farming in the winter-rainfall area" (1950).
Marais was chairman of the Dried Fruit Board until his death, was a member of the council of the University of Stellenbosch and served as technical adviser to the Wheat Board for several years. In 1950 he represented South Africa at a Commonwealth Agricultural Congress in the United Kingdom. He was honorary life president of several agricultural unions. As a sportsman he played rugby in the university's first team for several years and in 1922 played for the Western Province.
On 18 December 1923 at Stellenbosch he married Maria Henrietta Neethling, with whom he had four daughters.
