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Crop diversity on the decline nationally

Crop diversity on the decline nationally

USDA and university research shows farmers are growing fewer types of crops in the U.S. when compared to 30 years ago

University researchers are trying to determine how crop diversity – which is on the decline compared to 34 years ago – may impact climate change and the ecosystem down the line.

A large-scale study by Kansas State University, North Dakota State University and USDA is the first to quantify crop species diversity in the U.S. using an extensive database over a relatively long period of analysis, according to Jonathan Aguilar, K-State water resources engineer and lead researcher.

Related: Crop rotation good for soil microbes, plant growth

USDA and university research shows farmers are growing fewer types of crops in the U.S. when compared to 30 years ago

USDA-ARS rangelands expert John Hendrickson, weeds experts Greta Gramig, NDSU, and Frank Forcella, USDA-ARS; agricultural economics expert David Archer, USDA-ARS; and soils expert Mark Liebig, USDA-ARS joined Aguilar on the team.

Crop diversity is a measure of how many crops in an area can work together to adjust to or resist widespread crop failures.

"This could also be viewed as a way to spread potential risks to a producer," Aguilar said. "Just like in the natural landscape, areas with high diversity tend to be more resilient to external pressures than are areas with low diversity. In other words, diversity provides stability in an area to assure food sustainability."

To complete the study, scientists used data from the 1978 through 2012 USDA Census of Agriculture, which is published every five years.

Croplands comprise about 22% of the total land base in the lower 48 states, so changes in crop species diversity could have a substantial impact, not only on agroecosystem function, but also the function of surrounding natural and urban areas.

Because croplands are typically replanted annually, theoretically crop species diversity can change fairly rapidly. There is the potential for swift positive change, unlike in natural ecosystems.

In addition to the national trend, the researchers studied regional trends by examining county-level data from areas called Farm Resource Regions developed by the USDA's Economic Research Service.

Regional differences
Although the study showed that crop diversity declined nationally, it wasn't uniform in all regions or in all states.


"There seem to be more dynamics going on in some regions or states," Aguilar said, noting that not all of the factors affecting those regional trends are clear.

Related: More Similar Human Diets Signal Demise of Local Crops, Study Shows

For instance, the Heartland Resource Region – Illinois, Iowa, Indiana and parts of Ohio, Missouri, Minnesota, South Dakota, Nebraska and Kentucky – is home to 22% of U.S. farms. It represents the highest value (23%) of U.S. production, had the lowest crop diversity.

In contrast to all of the other regions, the Mississippi Portal Region, which includes parts of Louisiana, Mississippi, Kentucky and Arkansas, had significantly higher crop diversity in 2012 than in 1978.

While overall, the national trend was toward less crop diversity, the region called the Fruitful Rim (parts of Washington, Oregon, Idaho, California, Arizona, Texas, Florida, Georgia and South Carolina) and the Northern Crescent (states along the northeast border from part of Minnesota east through Wisconsin, Michigan through to Maine and south to New Jersey and Pennsylvania) had the most crop diversity.

The data used was specific enough that the researchers were able to quantify crop diversity and trends even down to the county level.

"A significant trend of more counties shifting to lower rather than higher crop diversity was detected," the team wrote in the study results.

The clustering is a trend toward diversity loss, they said which "could have far-reaching consequences" for the ecosystem and food system sustainability.

Biodiversity, for example, is linked to nutrient and water cycling, pest and disease regulation, and degradation of toxic compounds such as pesticides. Diverse agroecosystems are more resilient to variable weather resulting from climate change and often hold the greatest potential for such benefits as natural pest control, the researchers said.

A classic example where high crop diversity could have been crucial was during the corn leaf blight epidemic in the 1970s, Aguilar said.


During the 20th century, increases in the value of human labor, changes in agricultural policies and the development of agricultural technologies led to increased specialization and scale of production.

Economic and social factors helped drive the adoption of less-diverse cropping systems.

One consequence of less diversity could be the potential for unstable yields – even as weather patterns become more unpredictable.

Related: Corn Belt just as diverse now as it was in 1930

"Diverse cropping systems tend to increase farmers' chances of encountering favorable conditions while decreasing the probability of widespread crop failures," the team wrote, citing a study based on long-term data collected in Ontario, Canada.

In addition to quantifying the changes in crop diversity, Aguilar said, the scientists hoped to spur further studies and research with regard to changing agricultural condition and status.

"The factors that affect crop diversity in North Dakota do not necessarily apply to what is happening here in Kansas. This study also has relevance to other agronomic and environmental issues," he said, adding that the research has already generated inquiries from scientists who are studying weed resistance to herbicides, honeybee "friendliness" of the landscape and agricultural community resilience to pressures such as climate change.

The results of the effort, partially funded by the K-State Open Access Fund, were published Aug. 26, 2015, in the scientific journal PLOS One.

Source: K-State

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