Organic farming methods produced crop yields that were, on average, 20 percent smaller than conventional crops, during a 21-year comparison of the two methods. But, the organic approach more than made up the difference in ecological benefits, according to Swiss scientists who conducted the study. Their results appear in the journal Science, published by the American Association for the Advancement of Science.
In one of the longest-running studies of its kind, Paul Mäder of the Research Institute of Organic Agriculture, in Frick, Switzerland, and his colleagues compared plots of cropland grown according to organic and conventional methods. In each system, they grew potatoes, barley, winter wheat, beets, and grass clover.
"There is a need to evaluate alternative farming systems as a whole system in a scientific way. The most appropriate method to do this is still to conduct long-term experiments, which can be analyzed statistically and performed under identical soil and climate conditions. Soil fertility and biodiversity develop slowly, and this is why a long-term study is essential," Mäder said.
Unlike conventional farming, organic farming uses no synthetic fertilizers or pesticides. The authors also studied an organic approach called biodynamic farming, which requires some additional activities, based the environmental and spiritual philosophies of its inventor, Rudolph Steiner. Crop rotation, varieties, and tillage were identical in all systems.
Overall, the organic systems were able to produce more with less energy and fewer resources, the researchers report.
"These results should be encouraging for farmers, because they can see that yields are stable over time, and that soil fertility has increased," Mäder said.
Mäder's team found that over the course of the study, the amounts of nitrogen, phosphorus, and other nutrients added to the soil were 34-51 percent lower in the organic systems than in the conventional systems. But, because the crop yields from the organic systems were 80 percent as large as those from the conventional systems, the organic systems seem to use their resources more efficiently, according to Mäder.
The organic soils were also more fertile in other key ways, the scientists found.
The organic soils were home to a larger and more diverse community of organisms, Mäder and his colleagues report. This was true for soil microbes, which govern the nutrient cycling reactions in soils, and for mycorrhizae, root-colonizing fungi that help plants absorb the nutrients. These fungi were also at least partly responsible for the more stable physical structure of the organic soils, the researchers said.
Insects were almost twice as abundant and more diverse, including pest-eating spiders and beetles. Earthworms were more abundant as well. The weed flora was also more diverse in the organic systems, including some specialized and endangered species, the researchers found.
"Our results suggest that, by enhancing soil fertility, organic farmers can help increase biodiversity," Mäder said.
The organic soils also decomposed more efficiently, the researchers found. This is an important feature of fertile soil, Mäder explained, because the process releases nutrients and carbon to be used by the plants and microbes.
In Europe, both organic and biodynamic farming are well-regulated by national governments, in accordance with standard set by the European Union, Mäder said.
The other authors of the study are Andreas Fliessbach, and Urs Niggli, of the Research Institute of Organic Agriculture, in Frick, Switzerland, and David Dubois, Lucie Gunst, and Padruot Fried, of the Swiss Federal Research Station for Agroecolgy and Agriculture, in Zürich, Switzerland. This research was funded by the Swiss Federal Office for Agriculture and the Swiss National Science Foundation.