Study of U.S. farm data shows loss of crop diversity

U.S. farmers are growing fewer types of crops than they were 34 years ago a study by Kansas State University, North Dakota State University and the U.S. Department of Agriculture found. This could have implications for how farms fare as changes to the climate evolve and less crop diversity impacts the general ecosystem.

The scientists used data from the USDA’s U.S. Census of Agriculture, which is published every five years from information provided by U.S. farmers. The team studied data from 1978 through 2012 across the country’s contiguous states.

While the results did differ from region to region, “at the national level, crop diversity declined over the period we analyzed,” Jonathan Aguilar, K-State water resources engineer and lead researcher on the study, said in a recent article.

In all, croplands comprise about 408 million acres or 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.

“At the very simplistic level crop diversity is a measure of how many crops in an area could possibly work together to resist, address and adjust to potential widespread crop failures, including natural problems such as pests and diseases, weed pressures, droughts and flood events,” Aguilar said in the article. “This could also be viewed as a way to spread potential risks to a producer. 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.”

The study is the first to quantify crop species diversity in the U.S. using an extensive database over a relatively long period of analysis and in addition to the national trend, the researchers studied regional trends by examining county-level data. Although the study showed that crop diversity declined nationally, it wasn’t uniform in all regions or in all states.

For example, the Heartland Resource Region, represents the highest value, 23%, of U.S. production, had the lowest crop diversity. This region comprises Illinois, Iowa, Indiana and parts of Ohio, Missouri, Minnesota, South Dakota, Nebraska and Kentucky.

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

“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 and shifting demonstrates a trend toward crop diversity loss and attendant homogenization of agricultural production systems, which could have far-reaching consequences for provision of ecosystem services associated with agricultural systems as well as food system sustainability.”

Biodiversity in agricultural systems is linked to critical ecological processes such as nutrient and water cycling, pest and disease regulation, and degradation of toxic compounds such as pesticides, the article states. 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.

“An important consequence of increased crop homogeneity is the potential for yield instability with anticipated increased unpredictability in weather patterns linked to climate change. Diverse cropping systems tend to increase farmers’ chances of encountering favorable conditions while decreasing the probability of widespread crop failures,” the team wrote.

In addition to quantifying the changes in crop diversity, Aguilar said in the article that he hopes these findings will spur further studies and research with regard to changing agricultural condition and status.

“This study also has relevance to other agronomic and environmental issues,” he added. 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.

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Farm Resource Regions of the U.S.
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