The importance of long-term trials in understanding sustainable farming systems: the Rothamsted experience

This paper gives examples of how long-term experiments can be used t o improve our understanding of sustainable farming systems. Rothamsted conducts more than 20 long-term (>20 years) experiments in south-eastern England; several were started in the middle of the last century. Some have continued with minor changes, others have been modified considerably t o ensure their continuation and relevance. Examples are given of the effect on soils and crop yields of organic matter, the availability of P, and acidification. The use of archived material in addressing problems not even considered when the experiments began is also discussed. Long-term experiments are essential in determining the factors affecting soil fertility and sustainable production. In many cases, effects may only be observed or interactions become apparent over an extended time. Full use should be made of existing experiments and data; in particular, those on different soil types and under different climatic conditions should be compared so that the information is valuable to farmers, advisers, legislators, and other scientists in both the local and wider community.