Even though we are a month or so away from the ideal time to plant an overwintering cover crop, adequate planning begins now. Cover crops can play a role in managing nutrients, improving soil health, and suppressing pests. We receive several inquiries each year from producers regarding choosing the proper cover crop for their production system. We hope this short article can narrow down the options.
Cover Crop Choice
You must ask yourself “what is the end goal?”. Different cover crops can provide various benefits. Are you trying to add nitrogen for your crops the following year? Are you trying to add carbon to improve soil quality?
Legumes can provide a significant nitrogen contribution to your soil. The amount is impacted by:
- Legume choice (vetch vs clover), but also the variety of that legume (‘Lana’ vetch vs hairy vetch)
- Cover crop planting time (where earlier planting can increase nitrogen release the following year)
- Cover crop termination time
- Current soil nitrogen levels
- Seeding rates
- Single stand vs. mix
- Carbon:Nitrogen (C:N) ratio of the cover crop
Adding carbon to your soil via cover crops can have several soil quality benefits. In production systems that require frequent tillage activities, incorporating a cover crop with a high C:N ratio can help add carbon back to your soils. Cereal grains such as wheat or rye can produce considerable amounts of plant biomass and subsequent carbon. Delaying spring termination can increase the C:N ratio, but will lock up plant available nitrogen in the short term.
Cover crop mixes are currently very popular and promise several simultaneous benefits as compared to single-stand plantings. The ratio of the different cover crops in the mix will impact the above mentioned benefits. Research in western Washington has found many productive mixes that can become quickly established and supply plant available nitrogen the following year. One other benefit of mixes is that they can reduce the overall cost of seed. For example, cereal rye is very cold tolerant and can withstand those northeastern arctic lows over the winter, but can be mixed with wheat or oats to reduce the overall seed cost as compared to a pure stand of cereal rye at similar seeding rates.
One last note regarding cover crop seeding. Many producers inquire about broadcast versus drilling cover crop seed. In most cases, drilling results in an overall better cover crop stand as compared to broadcasting seed. This is a the result of better soil to seed contact. Broadcasted seed should be lightly incorporated with a mechanical tool such as a disc or roller to improve soil to seed contact.
Below are some really good resources for more information. Happy cover cropping!
Managing Cover Crops Profitably
Estimating Plant-Available Nitrogen Release From Cover Crops
WSU Puyallup Organic Farming Systems and Nutrient Management
Living on the Land: Guide to Growing Cover Crops
Establishing Winter Cover Crops
Organic Fertilizer and Cover Crop Calculator
Cover Crops for Home Gardens West of the Cascades