AgBioResearch

HICKORY CORNERS, Mich. – A six-year research effort by Michigan State University (MSU) AgBioResearch scientists has found a big difference in the yields produced by alternative agricultural practices in commercial fields compared with the same practices in the small experimental plots ordinarily used to test them.

These differences have important implications for closing the global yield gap between research plots and farmer fields, especially for low-input practices adopted by organic farmers in the United States and by resource-strapped farmers in less developed regions.

Published in the latest issue of PNAS, the research -- conducted by the Long-Term Ecological Research (LTER) team at the MSU W.K. Kellogg Biological Station (KBS) -- compared the yields of a crop rotation of wheat, corn and soybeans under three different management practices: conventional, low-input and organic. The tests were conducted at both small experimental plots and the much larger commercial field level. Though researchers found no appreciable difference in the yields produced at either level for conventional crop management, they noted a significant yield gap for both low-input and organic management.

According to Sasha Kravchenko, lead author and professor in the MSU Department of Plant, Soil and Microbial Sciences, this difference can be attributed to the additional challenges that large-scale production presents to both low-input and organic practices. Conventional management relies on the uniform application of chemical inputs such as fertilizer and pesticides, practices that can easily be scaled up to larger fields. In contrast, low-input and organic management require much more labor-intensive work, as well as the cultivation of cover crops, which is more difficult to perform consistently on large tracts of land. Because of the difficulty of scaling up low-input and organic practices to commercial fields, those farmers may see as much as a 30 percent lower yield than research suggests.

“The big conclusion is that, when you have management practices that require a lot of time and effort, and when the success of the practice requires more work than a farmer could reasonably do in an entire farm, then we as scientists need to adjust our recommendations,” Kravchenko said. “Our study shows that if you don’t invest in field-scale studies, you run the risk of recommending impractical methods that won’t produce the promised level of return.”

Kravchenko’s team found a number of factors that influenced the yield gap between experimental plots and commercial fields. One of the most significant factors was the need for cover crops. Because low-input and organic agriculture do not rely on chemical fertilizers, low-input farmers must instead look to cover crops such as red clover to enrich their soil with nitrogen. Chemical fertilizers can be spread uniformly, but the variability in elevation, soil quality and moisture levels present in commercial-scale fields means that cover crops may not perform at the same level throughout, resulting in uneven soil health benefits and subsequently reduced yield overall. In a smaller experimental plot, more care can be taken to ensure that cover crops are established and flourish. This level of maintenance becomes less practical in a larger setting.

The team also found challenges in weed management. Without access to the same volumes and types of chemical sprays to control weeds in conventional systems, low-input and organic farmers must use more time-consuming methods such as rotary tilling in their fields. This can provide sufficient weed control in smaller plots, but again, when scaled up to commercial levels, the practice can become impractical without the right access to labor.

“These findings show that we need to pay more attention to scale in our research, as farmers face tradeoffs and time-sensitive use of resources,” said Sieg Snapp, professor in the Department of Plant, Soil and Microbial Sciences and a researcher on the team. “This needs to be reflected in our recommendations for more sustainable farming.”

These results were made possible by the long-term resources available to the KBS LTER program, which  allowed the team to study and compare two full crop rotations in entire fields in all three management systems.

“Very few places in the world have the capacity to conduct replicated field-scale experiments,” said Phil Robertson, university distinguished professor of ecosystem science and LTER leader, “and even fewer for more than a year or two. But as this research shows, such experiments are crucial for answering important questions about how to convert research findings to farmer practice and thus how to feed a growing world with expanding food demands.”

Kravchenko said she hopes that this work will highlight the need for more field-scale experiments to provide farmers with the best, most practical information they need.

“My biggest hope is that the study raises awareness,” Kravchenko said. “Some level of discrepancy between findings from small plots and what farmers will experience is always anticipated, but this work shows that such discrepancies can be profound. Large field experiments aren’t just a luxury but something that must be done, especially for testing practices that require extra skills and labor.”