Perspectives: Asking a few thousand experts about soil health and hydrology

Sam Zipper, Kansas Geological Survey assistant scientist and assistant professor at the University of Kansas

Many people say the first principle of soil health is to “know your context” — meaning that a soil health management strategy should be based on a farm’s unique conditions, including its goals, climate, equipment, personnel and economics.

However, most published research on the impacts of soil health management practices, such as cover crops, conservation tillage and diverse crop rotations, have been conducted at a single site, often a research plot at a university experimental farm. Plot-based studies are typically designed to be statistically identical replicates rather than exploring the range of context variability. While this is useful for isolating the impacts of specific practices on outcome variables, it can be hard to predict what will happen when soil health management practices are implemented somewhere else based on these site-specific studies. This creates a major challenge for targeting and accounting for soil health management practices in a commercial setting.

However, beyond the published research, all these past studies have produced a byproduct — lots of researchers and practitioners with expertise and experience in soil health practices. To try and harness this knowledge, in connection with the Dairy Soil & Water Regeneration (DSWR) project, I worked with an interdisciplinary group of researchers with expertise in survey methods, soil health practices and agricultural production systems to carry out an “expert elicitation,” a research method intended to synthesize knowledge from lots of individuals. Specifically, we put together a survey asking people how they thought soil health practices would impact environmental outcomes like hydrology, soil carbon storage and crop productivity in their region, as well as how they expected hydrologic conditions, such as water table depth or soil drainage status, to impact the effectiveness of soil health practices to achieve goals like increasing crop yield.

We sent this survey out to about 4,000 soil health and hydrology experts, including researchers, conservation professionals, agency staff and others working in North American agricultural systems, and received about 400 responses.

The responses allowed us to integrate knowledge and insights from most of the U.S. and Canada. We found that, while the specific types of soil health management practices people used differed by region, across North America there was widespread agreement that soil health practices could provide benefits such as increasing infiltration, enhancing soil carbon storage and reducing nutrient losses.

We also found, however, a perception that local hydrologic and landscape conditions, such as high versus low spots in a field or watershed, had a strong influence over the effectiveness of soil health practices to achieve farm goals.

Across most of the practices we asked about, the perceived benefits of soil health practices were facilitated through hydrologic changes. For example, our respondents suggested that cover crops could both lead to a direct reduction in nitrate losses but also reduce hydrologic losses of nitrate by enhancing soil water retention.

This elicitation helped us collect opinions about the relationship between soil health and hydrology from a wide swath of experts, while targeting our research efforts within the DSWR project. Since DSWR is fairly unique in its design, with a consistent data collection and modeling effort across many regions, we can use these cross-regional expert opinions to help us identify what variables and processes to focus on.

We are looking forward to comparing the field results from DSWR to these survey responses to help us learn more about how soil health practice effectiveness and interactions with hydrology vary based on local context.