By Kristin Williams, Agronomy Outreach Professional

We just finished a two-year, multi-farm study on the health of clay soils, funded through a VT Conservation Innovation Grant through the NRCS. Measures of soil health (using Cornell’s soil health test) were not consistent, and we found that comparing practices over time was more informative than comparing field to field. One interesting, and maybe
obvious, lesson was the correlation between soil health practices and crop yields.

So, how do soil health practices influence yield? Research suggests soil health can improve yields. It is important to note our project focused on  demonstration, not replicated research. We compared no-till and conventional/reduced till corn silage on 5 farms with clay fields in our region. A simple t-test revealed no significant difference in yield between no-till (19.1 tons/acre) and conventional (19.2 tons/acre). More importantly, we were able to demonstrate that a farmer can grow no-till without yield losses, and be successful with good management practices. A yield gain might take time as the soil builds up its condition.

We also wondered how cover crop species or mixes might affect corn silage yield. We had an opportunity to use a field where the corn was accidentally killed. We planted 15 different combinations, including 4 single species, 6 two-way mixes, and 5 three-way mixes. This project was a slight anomaly in that the cover crops were planted with a drill in late August, which allowed for a more vigorous production of all cover crops. Radish was a star in the fall, maximizing both phosphorus and nitrogen uptake. We did not measure phosphorus content in the spring, so we do not know how much was retained in the soil. It seems to have allowed
for more available nitrogen in the soil at the time of a pre-sidedress nitrogen test (PSNT), therefore requiring less nitrogen. Surprisingly, legume mix covers had good fall biomass, but that did not translate into more N mineralization.

We applied nitrogen to each plot as per the PSNT recommendation for 20 tons/acre corn silage. At the end of the season, we measured corn silage
yield and compared that to nitrogen applied (see graph). The winter rye plot had a lower corn silage yield and required more nitrogen. Other than the nutrient effect of less uptake and slower decomposition, there may have been a physical barrier created by the standing rye crop, which was particularly vigorous in the spring. However, our three-way mix (winter rye – oats – radish) actually had the highest average corn silage yield, even though it required more N at PSNT time than the pure radish stand.

So, do not go abandoning your winter rye just yet. In fact, we think this three-way mix has promise and we are looking for a mix that gives both fall and spring soil conservation. Radish alone will winter kill, which may be good for mineralization, but not as good for spring soil conservation. Oats also winter kill but provide faster fall soil cover than rye by itself.

When using an over-wintering cover crop, it is clear that timing and success of termination is critical for subsequent crop yields. Nitrogen mineralization may happen later in the season with a plant such as winter rye that has a heavier carbon content. In a no-till system particularly, you may need to adjust your nitrogen rates/timing and put more on upfront. If you are using cover crops, a PSNT seems like a wise investment.

It is also important to remember that soil health is a long game, and it may take time to see the results of your labors with cover crops. We have replicated this project by replanting these cover crops in the fall of 2016, this time planted in September, and will look at this again this coming season.

More info about UVM’s PSNT test can be found at: