Gradual, episodic or subtle changes in agroecosystems can be definitively measured only in long-term studies. The objective of this paper is to illustrate the benefits and limitations of long-term agroecological sites using a crop rotation study (Rotation ABC) established at Lethbridge, Alberta in 1910. Long-term agroecological sites, envisioned as part of a continuum of research levels, seek to determine the persistence of cropping systems with respect to their effects on soil resources and the larger environment. Examples of research findings arising from such sites include the documentation of long-term changes in agricultural productivity, measurement of organic matter changes over time, calculation of long-term nutrient budgets, and verification of simulation models. For example, soil organic matter concentrations in Rotation ABC were found to decline abruptly within the first few decades of cultivation and then approach a new steady state. Despite the continual removal of N in harvested grain, soil N concentrations also appear to have stabilized, suggesting an accession of N approximately equivalent to the amount harvested. Common limitations of long-term sites like that at Lethbridge include: rudimentary experimental design, evolving management practices, incidental changes at the sites, and variation in sampling protocols. The successful use of long-term agroecological sites depends on well-defined objectives, simplicity of design, adequate scale, consistent data and sample collection, and collaboration among sites. The primary justification for the establishment and maintenance of long-term agroecological sites may be their future role in answering questions not yet envisioned. Key words: Soil organic matter, long-term studies, crop rotations, sustainability, fertilizer
Differences in labile soil organic matter explain potential denitrification and denitrifying communities in a long-term fertilization experiment
