The Rothamsted Long‐Term Experiments: Are They Still of Use?

Abstract The Rothamsted long‐term experiments—the Classicals—were started almost 150 yr ago. These experiments were originally designed to study the N, P, K, Na, Mg, and Si needs of the field crops then grown in England. This was done by comparing these inorganic nutrients, in various combinations, with farmyard manure, the traditional source of fertility at that time. Although the questions the experiments were originally designed to answer have long been re‐solved, the experiments continue to give results of interest to agronomists, ecologists, soil scientists, plant pathologists, and others. The experiments show that grain yields can be sustained (and even increased) for almost 150 years in monocultures of wheat and barley given organic or inorganic fertilizer annually. They provide data on the long‐term effects of inorganic fertilizers and organic manures on soil organic matter levels. These data have been used to test computer‐based models for the turnover of organic matter in soil. Again, long‐term N balances show that there are considerable inputs of N to the soil/plant system, amounting to some 30 kg N ha −1 yr −1 in unfertilized wheat and up to 65 kg ha −1 yr −1 in an arable soil reverting to woodland. These and other results are used to consider the advantages and disadvantages of long‐term experiments. Wisely used, long‐term experimental sites provide information on the long‐term sustainability of agricultural systems that can be obtained in no other way.