Rooted in Data - Initial FindingsBy Maria Bowman on Thursday, 25 April, 2019
At this year’s Soil Health Summit, we were excited to present preliminary insights from the data we have been gathering on SHP fields over the last five years. We incorporated as much of the 2018 yield data as we could before the Summit in order to take a look at the impact of cover crops on corn and soybean yields, since cover crops are the most common practice that the farmers who partner with us are trialing on their fields. The data suggested that growing a cover crop didn’t have a statistically significant impact on average corn or soybean yields in our dataset from 2015 through 2018. Though we know this is not true of every farm, no significant difference in yield on average gives us a starting place to begin to look at impacts of cover crops on yield variability and under different weather conditions, as well as to look at the impact of different types of cover crops on yields.
We also took a look at how soil health properties are changing on some of the fields that have been working with SHP for 3 or 4 years. One thing we found was that soil organic matter in the Cornell soil health test increased between ⅓ and ½ percent, on average, over a 2-3 year period. Our preliminary results indicate that mean soil organic matter (OM) for SHP research strips is significantly higher in year 2 relative to baseline year (3.87% vs. 3.31%) at the 99% level for farms that tested in the baseline year and year 2, and that mean OM is significantly higher in year 3 relative to year 1 (3.94% vs. 3.59%) at the 99% level for farms that tested in years 1 and 3.
This graph shows mean changes in percent soil organic matter to a 6-inch depth, as measured using % loss on ignition by the Cornell Soil Health Lab, for two groups of farms participating in the Soil Health Partnership. The first group of farms sampled at baseline (Year 0) and in their 2nd year (30 farms in Illinois, Indiana, Iowa, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Wisconsin), and the second group of farms sampled in their first and third years (15 farms in Illinois, Indiana, Iowa).
However, when we looked more closely to see what might be causing this change, we found that both cover crop treatment strips and control strips were showing increasing organic matter over time, on average. Though we are still looking into why this might be, it’s really made us think about the importance of understanding where farmers are on their soil health journey and how that is reflected in changes in soil health indicators over time. Also, increased percentage of soil organic matter may suggest greater soil carbon storage (carbon sequestration), but not necessarily, especially since SHP currently samples to a six inch depth (see, for example, Yang and Wander (1999) and Pribyl (2010)). With our many research partners, such as The Soil Health Institute, we hope to further explore this connection and better understand the impact of agricultural management on soil carbon.
These two findings are just a starting place for our research on the impacts of soil health practices on soil health, agronomic outcomes, and profitability. In 2019, we look forward to building on these initial findings, including developing clear and realistic business cases to illustrate the impact of practices such as cover crops and tillage on farmers’ bottom lines
This graph represents mean corn yield data from a minimum of 8 farms (in 2015) and a maximum of 24 farms (in 2017) engaged in cover crop trials in Illinois, Indiana, Iowa, Ohio, Minnesota, Nebraska, and Wisconsin. In 2015, there were 33 control strips and 37 cover crop strips with corn yield data, and in 2017 there were 110 control strips and 123 cover crop strips with corn yield data.