Montana State experts offer way to assess and track soil health

BOZEMAN - When land managers modify their management to improve soil health, it is often challenging to measure and evaluate the soil's response.

"There is no optimum standard for soil health in the same way that there is an optimal body temperature for human health," said Cathy Zabinski, professor of plant and soil ecology in MSU's Department of Land Resources and Environmental Sciences.

Soil health varies greatly by soil type and climate, so Zabinski and Zane Ashford, a former graduate student, studied a site-specific indicator of soil health. The soil health gap is the difference in soil health characteristics between managed, disturbed land, which includes cultivated, hayed or grazed fields, and minimally disturbed land. It is expressed as percentages; the larger the percent, the greater the difference in each soil health characteristic between the two soils.

Ashford compared cultivated and uncultivated fields near Forsyth and Fort Benton and found a soil health gap of 40 to 60% for several indicators of soil health, such as the concentration of soil organic matter. The uncultivated sites were dominantly intact perennial plant communities, and the cultivated fields were under conservation farming practices to reduce soil disturbance, which included no-till, no summer fallow and rotation practices with perennials.

"We would expect the soil health gap to be even larger in a cropping system that uses tillage and fallow largely because those practices offer less soil cover and return less residue to the soil," said Clain Jones, MSU Extension soil fertility specialist and professor in the Department of Land Resources and Environmental Sciences.

Land managers can measure the soil health gap by comparing soil characteristics of multiple soil samples from a managed area of interest to a similar, nearby and minimally disturbed site. Jones said matching the slope, elevation and aspect of the two locations offers the best test results to compare.

While it can be difficult to find simple measures that characterize soil health, Zabinski and Ashford used biological indicators, such as soil enzyme activity, and chemical indicators, such as soil organic matter.

"If the land manager wants a detailed evaluation, they can test for several additional biological, chemical and physical soil health indicators, but this can quickly get expensive," Jones said.

Two online reference sheets, The Soil Health Gap and Evaluating Soil Quality and Health, provided by Jones' MSU Extension program, discuss many of the soil health characteristics that could be used.

Jones said tracking the soil health gap every five years over a period of 15-20 years may help identify specific changes in field management that benefit soil health. One of the best ways to increase soil health is to return more plant residue to the soil, he said. On cropland, this can be done by converting ground planted with annual crops to perennials or replacing fallow with a crop. For pasture or hay fields, soil health can be improved by addressing factors that limit production, such as poor soil fertility, soil acidity, weeds or overgrazing.

For more information on the soil health gap and soil health characteristics, visit The Soil Health Gap and Evaluating Soil Quality and Health. Additional reference sheets on soil health are available through Jones' The Soil Scoop fact-sheet series.