There is a growing perception that present trends in global agricultural
production are neither sustainable nor environmentally sound.
But that view isn't necessarily based on scientific data. Only experiments
that have been meticulously carried out for several decades can answer
questions about the sustainability of agricultural practices.
That's because changes in key indicators, such as soil organic matter, can
take more than 20 years to become detectable by current analytical methods. And
short-term experiments may miss the impacts of management changes because the
measurements are taken while the system is still in transition.
As early as 1843, scientists in Rothamsted, England, established long-term
agricultural experiments to learn how crop management techniques influenced
yield and soil quality over time.
Later, researchers in the United States and other countries set up similar
long-term projects. Some of those experiments are still running todaylike
the ones described in this issue that were established in 1931 at Pendleton,
Long-term experiments can identify management practices capable of
maintaining crop yield and soil quality. They show, for instance, that plowing
under the plant material left behind after harvestthe crop
residueincreases soil organic matter and reduces erosion.
But even as we transfer technology that supports sustainable agriculture, we
have to be culturally sensitive. Growers in a developing country may readily
adopt new tillage machinery. But because they need the leftover straw for feed
and fuel, they may not be able to commit to techniques such as residue
management. That makes it even more important to understand the impacts of
various agricultural techniques and to develop better management practices.
Long-term experiments can also reveal unfavorable effects of agricultural
practices, such as the repeated addition of ammonium- or urea-based nitrogen
fertilizer without the concurrent addition of lime. That can make the soil more
acidic. Highly acid soil is detrimental to crop growth and biological activity
Experiments like those at Pendleton have a much wider application than
agriculture. They probably make up the largest temporal and spatial database
currently available for determining impacts on any ecosystem. As such, they
afford the possibility of harnessing observations of past change to predict
Internationally, the NATO-sponsored Soil Organic Matter Network, SOMNET,
seeks to predict the effects of climate, atmospheric composition, and land use
change on soil organic matter. Researchers are using data from several
long-term experiments to judge the accuracy of computer models in simulating
Projects are evaluating the soil's ability to serve as a sink for carbon to
mitigate global climate changes. Soil contains twice the amount of carbon as
does the atmosphere, and it appears capable of storing much of the increase in
atmospheric carbon dioxide if key agricultural practices are adopted.The best
long-term experiments also have an archive of soil samples that contain
benefits never imagined by the experiments' founders.
For example, soil samples have been collected and archived at Rothamsted
since 1843. Now, scientists can analyze these samples to determine how the
levels of potentially toxic elements, such as cadmium and certain dioxins, have
been changing in the soil.
A key objective for the future will be to identify and support long-term
experiments that have been managed properly. Most of those existing today have
survived war, drought, and politics. Commitment is needed to ensure the
continuance of those with relevance and merit, as they offer invaluable insight
into the research best able to guide us in the 21st century.
Paul E. Rasmussen, ARS
Columbia Plateau Conservation Research
Center, Pendleton, Oregon.
[Parts of this Forum were adapted from an article by the author titled
"Long-Term Agroecosystem Experiments: Using the Past To Guide the
Future," which appeared in the October 30, 1998, issue of
published in the February 1999 issue
of Agricultural Research magazine.