A new approach to soil testing for Michigan farmers: from inputs to indicators of soil health

Each year the KBS LTER program awards two graduate students with summer research fellowships. Here Brendan O’Neill describes the research his summer fellowship supported. Brendan is a Ph.D. student in Tom Schmidt and Phil Robertson’s labs.

My research at the Kellogg Biological Station Long-term Ecological Research (KBS LTER) site has focused on how increasing crop diversity (for example, including cover crops) can enhance soil ecosystem functions while sustaining crop production. Examples of soil ecosystem functions include retaining carbon (C) and nitrogen (N) within the field and managing soil structure to supply both ample water but good drainage. By contrast, for decades, row-crop research has focused on supplying chemical components like fertilizer as the means to maximize crop productivity; this research shaped soil tests that guide farmers’ soil management. Traditional soil tests focus on the chemicals needed for plant growth, such as nitrogen, phosphorus and potassium, ignoring the combination of physical, chemical and biological conditions needed for a healthy soil ecosystem.

KBS LTER grad Brendan O'Neill samples soil on a Michigan farmer's field.

KBS LTER grad Brendan O’Neill samples soil on a Michigan farmer’s field.

Nitrogen use in agriculture aptly demonstrates how simply supplying crops ample chemical N, rather than focusing on the biology of how soils can use N efficiently, has consequences far beyond crop yield, leading to N contamination to waterways and the atmosphere. What if we used indicators of healthy soil ecosystems in soil tests to help guide management for farmers, expanding soil tests to include biological and physical parameters? This was the focus of my 2014 KBS LTER Summer Research Fellowship.

Working on experimental systems at KBS, I realized some components of measuring healthy soil are rapid, inexpensive and sensitive to management differences. I decided to collaborate with MSU Extension staff and Michigan farmers to measure over 15 different soil parameters, from traditional chemical measures such as mineral nitrogen, phosphorus and pH, which farmers are used to seeing, to a new set of indicators of soil ecosystem health, such as tests for soil aggregation and compaction, and rates of C and N turnover by soil biota. My colleague Christine Sprunger and our summer undergraduate REU Alee Zuninga were part of this effort. In 2014, we asked farmers across Michigan to identify a range of their fields from ‘best’ to ‘worst’, including a field that was not in row-crop production. We worked in three Michigan counties with different soil types and sampled a range of KBS LTER treatments in order to have a wide array of values from which to assess well-managed soils.

Our team compared results from traditional soil tests—unchanged for decades and centered on an ‘input-based’ approach to soil fertility—with results from the new test parameters. We used some rapid and proven tests for soil ecosystem health, including tests for stable soil aggregates and N supplied by soil microbes. We also tested new indicators, including tests for rapid C turnover and soil nitrification, an indicator of how vulnerable N may be to leaving the field through air or water. Our goals were two-fold: first, we wanted to ‘test the test’ to see how sensitive our soil ecosystem health tests were to a range of farmer fields. Second, we wanted to present the results to farmers to assess their interpretation and understanding of the soil health parameters. After all, farmers are the ones who will use such tests and hopefully manage based on indicators of soil ecosystem health.

Our results were striking on numerous levels. Chemical parameters from traditional tests differed little across the range of fields. Farmers have traditionally managed based on test results for soil chemistry and the fact that their ‘best’ and ‘worst’ fields differed little indicates they are ‘managing to the test’. That is, even though production varied across their best and worst fields, the soil chemical parameters measured by traditional soil tests did not reflect that.

In sharp contrast, the soil ecosystem health indicators, measuring the biology and physical aspects of soil, revealed a wide range of results between ‘best’ and ‘worst’ fields. This shows how well farmers know their fields: when asked, all knew immediately which were their best and worst fields, and the soil ecosystem test results bore out their intrinsic knowledge. These parameters indicated why some of these fields might be underperforming. In the ‘worst’ fields, soil was compacted and poorly aggregated (leading to soil crusting) and had reduced turnover of C and N as indicted by biological tests.

Since compiling the results we have been meeting with growers individually to discuss the histories of each field and share the results of the two approaches to testing. All the farmers were struck by the differences showed by the new sets of ecosystem parameters compared to traditional soil test results. In addition, learning in depth their experience of each field—how it was managed, various recurrent problems, challenges within each field—added a critical narrative to accompany the quantitative results generated by the tests. Our research team greatly valued gaining this deeper understanding.

All growers wanted to know how to use test results to improve their management. Soil ecosystem health depends less on external inputs and more on management approaches such as reduced tillage, better N management and increased cropping system diversity. These practices can reduce the need for external inputs (and their adverse effects) by enhancing soil ecosystem processes that retain nutrients. Many of these practices require careful planning and altered management over longer time scales. It is unclear if farmers will adopt some of these management strategies, but the hope is that having measurable soil ecosystem health parameters will help farmers see if they are headed in the right management direction. Discussing the new test results with farmers is an important step toward managing for soil health. In turn, farmers provided our team with key links between what they experience in each field and how that relates to test results.

The Summer Fellowship allowed for travel to different counties across Michigan, for the equipment needed to test for soil health, and for running soil tests from over fifty farmer fields and the KBS LTER experiment. However, the effect of this work is broader. It provided early resources to generate data to secure USDA Sustainable Agriculture Research and Education (SARE) Graduate Student Grants for me and Christine, and it enabled collaborations that would not have been possible otherwise. In the near term, an Extension bulletin will be published that uses both the test results and the feedback from farmers to disseminate important information on soil health to a wider audience. Longer term, there is growing interest within the MSU Extension community to continue and build on these tests to help Michigan growers manage for soil health.