Northwest Wisconsin Long-term Test Plot Shows Tillage and Covers Effects on Profits, Yields, & Soils

The Horse Creek Farmer-Led Watershed Council, with the help of Carlson Family Farms & Timm Johnson, maintains a test plot north of New Richmond to compare yield data between five trials replicated 3 times over the 15 plots:

1. No-till with no covers (bare)

2. No-till with multi-species cover crops

3. No-till with rye cover crops

4. Tilled with rye covers

5. Tilled with no covers (bare)

The test plot is laid out with 3 replications of the 5 trials with roughly 1/8 of an acre plots.

Yield Results since 2015

Since 2015, the farmers with help from Polk County Land & Water Resources Department staff have measured yield, test weights, and residue cover on each of the plots. Analysis of yield has shown that each trial has had the most and almost the least yield of all other trials and in at least one year since 2015. While this does not paint the simple picture some conservationists might hope (that cover crops and no-till consistently out-perform tillage and bare soil) it does show that intentional conservation practices don’t affect the yield nearly as much as conditions of the season.

We see much more consistency between plots in the same year than we see between plots of the same trial in yield. This is not surprising since mother nature’s seasonal variation plays a bigger role than we do.

2022 was a particularly challenging year on the test plot due to poor population. Late spring showed poor emergence on the trial which was attributed to soil crusting and a cold spring rain after planting which especially impacted the tilled plots. In fact, these conditions led to the greatest variation between trials we’ve seen within one year.

Calculating Profits per Trial

Knowing this information about yield over the last 8 years, our next question was to look at profit and management costs. If the yield is on par with less intentional management but costs more in terms of labor and input costs then we need to know that, especially in a year of higher input prices. While it is always difficult to break down every cost of planting, maintenance, and harvest in a year, the landowner, Timm Johnson, has attempted to do that for 2021 and 2022.

All plots were treated the same in terms of custom planting, herbicide, rolling (on soybean ground), fertilizer, and land rent. The differences between plots were calculated to $18/acre for tillage (which is conservative considering the cost of diesel), $25/acre for rye cover crops and $40/acre for multi-species cover crops. In 2021 the corn was sold for $6.80/bu and in 2022 the food-grade soybeans were sold for $15.00/bu.

Field Erosion:

Method of tillage and cover crop usage represent more than just different field management methods. How farmers use these practices has a big impact on erosion of soil from fields, infiltration of rainwater, and thus fertility needs of crops grown on the fields. This potential fertility difference is hard for us to truly analyze with the test plot as we don’t want to change other variables such as fertility or herbicide programs. Early analysis shows that the plots with soil health practices (cover crops and reduced tillage) have 10 times as many worms per square foot than the tilled plots with no cover crops. A rainwater infiltration study of the Horse Creek plot in 2022 also showed that the relatively flat tilled plots lost 47 times more soil during a spring rain event than the no-tilled plots with rye covers.

The Horse Creek watershed was modeled to calculate just how much these practices impact erosion and nutrient loss from fields. Reducing tillage to standard no-till practices across the average field in the watershed (many of which have significantly more slope than our test plot) stops erosion of 680 pounds of sediment per acre and 3.18 pounds of nitrogen and 1.78 pounds of phosphorous per acre.

Dennis Busch presented this summer at the test plot showing how infiltration and runoff differed between each trial. The bottles in front of the graph show the sediment carried with runoff from each trial.

Similarly, models predict that planting cover crops reduces nitrogen loss off of fields by 1.88 pounds per acre. Cover crops also keep 100 extra pounds of sediment from running off of every acre and .53 pounds of phosphorous.

A transect survey in Polk county estimates that the average field in the county loses 4,200 pounds of soil per acre every year. While that soil is being lost (roughly a millimeter every 3 years), a generous estimate is that it takes about 20 years to create a millimeter of soil across an acre through natural geological processes.

Two Neighboring fields in the Horse Creek Watershed show the intensively tilled field (right) sits lower than its neighbor which has been minimally tilled for the last 40 years.

At those rates, we’re looking at a practical loss of resource, which you can see on any older fence line on a field. It is common to see a field sitting significantly lower than the soil around fence posts that have been undisturbed since originally put in by our fore-farmers less than a hundred years ago. The loss of that topsoil means a loss of fertility for crops and eventually a loss of a medium to grow crops at all. But beyond the basic arithmetic of gain verses loss of topsoil as a concern for farmers, that sediment ends up in ditches and surface waters.

Beyond sediment, nutrients of concern--especially phosphorous are lost during erosion. Those nutrients then end up in surface waters like Cedar Lake. Because of this, prevention of erosion is a prevention of algae. In 2022, Polk county staff inventoried 1,947 acres of cover crops, 2,892 acres of no-till, and 478 acres that had cover crops and no-till. Those practices kept 6,734 pounds of phosphorous out of surface waters. Knowing that 1 pound of phosphorous makes 500 pounds of algae, Horse Creek watershed farmers kept 3.4 million pounds of algae out of local lakes in 2022.

The Horse Creek Farmer-Led Watershed Council is a group of farmers working together to improve soil and water conservation within the Horse Creek watershed. Established in 2013, their mission is to help producers to adopt best management practices dedicated to protecting water quality and improving soil health.

Farmers interested in enhancing soil health and nutrient efficiency practices on their fields can connect with their local farmer-led watershed council. The Wisconsin Farmers Union supports four councils in northwestern Wisconsin through our Watershed Coordinator, Tara Daun, who can be reached at 715-492-0329 or tdaun@wisconsinfarmersunion.com.

More information on the Horse Creek Farmer-Led Council, including the full 2021 report on their test plot can be found at their website.