A recap of the Badger Crop Connect webinar on July 26, 2023
- Spring barley and oats are good options as “starter” cover crop species
- Winter rye provides coverage through the spring
- Will need to adjust manure-N credits when using winter rye
- No real value in seeding winter rye above 60 lb/ac
- Nitrogen is lost from fall-applied manure due to leaching. If it will be lost anyway we might as well tie it up in cover crop biomass.
Do cover crops do what we think they are doing?
Whether it’s reducing nitrates leached to groundwater, phosphorus to our water bodies or increasing soil organic matter and microbial biomass, the answer is generally yes. But in trying to integrate cover crops into a cropping system, what are the considerations–species selection, seeding, benefits and drawbacks–that need to be addressed along the way?
One key use may be nutrient uptake and reduced nitrate leaching from fall-applied manure. Dr. Matt Ruark and his lab tested several common cover crops planted after corn silage, including barley, annual ryegrass, and winter rye at Lancaster, Arlington, and Marshfield agricultural research stations to determine their nitrogen uptake and effect on following corn crop yield.
The good: While all the cover crops scavenged nitrogen that would have leached from the manure, winter rye was the obvious winner in preventing leaching.
The bad: In the case of winter rye, the corn took a yield hit and the amount of nitrogen required to hit the economic optimum nitrogen rate was higher than the non-cover cropped control, meaning that more nitrogen was tied up than would have otherwise leached from the fall-applied manure. Furthermore, as biomass of the rye increased, more nitrogen was required to reach similar yields as the non-cover crop control. These findings affect the manure credit in the spring that you can take from fall-applied manure.
|Cover crop biomass (lb/ac)
|Estimated N uptake (lb/ac)
|Amount to adjust manure N credit (lb/ac)
|No adjustments needed
|Subtract 35 lb/ac from manure N credit if winter rye was used*
|Do not take any manure N credit**
*There was no clear effect when winterkilled cover crops were used based on Wisconsin research
**This recommendation applies to manure N applications up to 100 lb/ac of available N
To avoid nitrogen tie-up and yield drag with winter rye–as the nitrogen is not returned to the soil in that growing season–terminate the rye as early as possible in the spring. Not much value was seen in increasing the seeding rate of rye beyond 60 lb/ac, other than tying up more nitrogen at planting. Even at lower seeding rates, soil coverage was more than 75% due to increased tillering. Rates could even be dropped further to save on seed costs while still achieving conservation goals. Finally, in years of dry conditions or drought, cover crops can take up water that the following crop needs as well, depressing yield potential. This can also be mitigated by terminating early.