By KAREN BINDER
Illinois Correspondent

URBANA, Ill. — University of Illinois soil scientists have dug into turn-of-the-century agronomy records to learn more about the organic richness of state prairie soils over the decades.

While a research team headed by UoI bio-geochemist Mark David has concluded that organic carbon and nitrogen levels have shifted along with different cultivation methods, those amounts have leveled off and remained constant since the 1950s.

“For these prairie soils, some of the best in the world, declines in organic matter from cultivation were likely completed by the 1950s, and since then organic matter pools have remained relatively constant under modern production practices,” David noted in a press release.

David’s team at the Department of Natural Resources and Environmental Sciences identified and resampled soils from 19 central Illinois locations, most of which had been tested in 1901 to 1904 or 1957. Another important time element in the study was the period from 1957-2002 when predominantly synthetic fertilizers were used.

The farm test locations also were poorly drained, planted in corn/soybean rotations and tile-drained, as well as having no known manure applications. The locations were compared against virgin prairie plots and historical data, including soil samples from the early 1900s and 1957. The results also confirmed previous studies.

“Declines in organic matter were likely completed by the 1950s, with organic matter pools in a steady state under the production practices in place from the late 1950s through 2002,” David said.

What this knowledge means for farmers is better understanding of soil changes. The study noted it’s been well documented previously that long-term cultivation and crop production affect organic C and total N levels, both factors critical to soil quality and productivity.

David said monitoring these changes is important because organic matter in soil is slow to respond to management shifts, such as use of tile drainage.

 “Most of the decline in organic matter occurred in the top 50 centimeters of soil, with evidence that carbon and nitrogen moved from the upper soil layers to deeper ones, possibly enhanced by tile drainage,” he said.

Cultivated fields had soil C and N concentrations typically 30-50 percent less than virgin prairie soils.

Smaller but significant declines in C and N concentrations were found when comparing 1900s cultivated fields to concentrations in 2002, after another 100 years of cultivation, and in comparing 1957 grass covered fields that had been converted to annual cultivation before 2002, according to the study.

 The reduction in organic matter after cultivation of prairies occurred mostly in the top 50 centimeters of soil, with evidence of translocation of C and N from these upper layers to the 50- to 100-centimeter depth, possibly enhanced by tile drainage, the study noted.

Another historical aspect of the study includes a step back 100 years, thanks to the work of Cyril Hopkins, the head of the Illinois Department of Agronomy from 1901-04 when the first soil samples were collected, pointed out study team member and soil scientist Robert Darmody.

Allowing invaluable insight were the glass jars of collected soils, Darmody said. These samples and those from a similar collection by the Soil Conservation Service in 1957 allowed chemical testing across the decades.

“Without the stored samples, it would have been difficult to know if the data could be compared to modern analyses,” environmental scientist Greg McIsaac stated in a press release.

 McIsaac noted that the UoI has a unique and large archive of soil samples from this early period and throughout the 20th century.