The crop rotation experiment, established by Vilmos Westsik in 1929, is the best known and most remarkable example of continuous production in Hungary. It is still used to study the effects of organic manure treatment, develop models and predict the likely effects of different cropping systems on soil properties and crop yields. Westsik’s crop rotation experiment provides data of immediate value to farmers concerning the applications of fertilisers, green, straw and farmyard manure. The experiment also provides a resource of yield, plant and soil data sets for scientific research into the soil and plant processes which control soil fertility, and into the sustainability of production without environmental deterioration. The maintenance of Westsik’s crop rotation experiment can be used to illustrate the value of long-term field experiments.