When should I terminate my cover crop

You’ve planted your first cover crop and it’s nearing time to plant your cash crop. When to terminate? This is a common question facing many first-time cover croppers and there are a lot of opinions around this topic. The best answer is delay termination as long as possible to gain maximum benefit of the cover crop without creating a problem for your cash crop. This is a broad statement and may not be very helpful at face value, therefore we will dive into context specific suggestions. 

First and foremost, discuss termination plans with your local crop insurance agent who should be up to speed on the most recent crop insurance guidelines through the Risk Management Agency (RMA) division of the USDA. See the USDA's RMA Cover Crop website which contains helpful information. Producers practicing no-till generally have a 7-day extension beyond the permitted termination date as described in the NRCS Guidelines Version 4. The key here is that crop insurance recognizes good management practices for cover crop management. That means that if an agronomic expert suggests a cover crop management strategy or the management strategy is common in your area, RMA will recognize it as meeting their guidelines.

Cover crops are fantastic for improving soil structure and aggregate stability while increasing organic matter. Delaying termination as long as possible and letting those covers grow can improve those characteristics even faster.  Farmers all over the country have reported soil infiltration rates improving from less the 2 inches of water per hour to well over 5 inches in a matter of 2 - 5 years after implementing cover crops and no-till practices.  Imagine the next time you have a 5-inch rainfall in less than an hour and every ounce of rain is absorbed by your soil. For every 1 percent organic matter added per foot of soil, your water holding capacity will increase by up to 20,000 gallons of water per acre which is incredibly valuable during a persistent dry spell or drought.  

There are situations where it is not advisable to delay termination and plant green. One example is when unusually dry conditions occur 2 – 4 weeks with no foreseeable accumulating rain for the next two weeks after planting.  If these conditions are common in your area, it may be valuable to terminate your cover crop 10 days to 2 weeks prior to planting, or sooner than planned. This will help preserve moisture for seed germination, especially when new to cover cropping. Veteran cover croppers will likely have a greater buffer due to their soils’ enhanced water holding capacity.

On the flip side, when you are experiencing an unusually wet spring, your best bet is delaying termination as long as possible and planting green where permitted. Living plants transpire and pull moisture out of the soil down to their rooting depth. In addition, live roots act as greater support, like rebar in concrete, when pulling a planter through the field. If cover crops are terminated too early, they can act like a mat potentially slowing evaporation and soil drying.

Most winter legume cover crops have maximum N production by mid bloom stage. Waiting to terminate until this point can be costly as it would likely delay planting until the last half of May or the middle of June most years.  However delaying termination as long as possible could be the difference between 20 or 40 additional units of nitrogen made available through N-fixation to the next cash crop.  

Are you interested in reducing your chemical bill? Roller crimpers can be a great alternative to herbicides for terminating your cover crop. Roller crimpers are generally effective for a limited number of cover crop species and require precise termination timing to achieve an adequate kill. For example, cereal rye is most effectively terminated when it reaches anthesis.  At this point, the stem has elongated to near max height and it is less likely to rebound after crimping. Cereal rye terminated earlier may stand back up and appear unphased.

Where permitted and after talking to your crop insurance provider, you may be able to delay termination longer than you expected. Yet planting date and type of cash crop may be the final influencer of cover crop termination date.  For example, soybeans are less affected by planting green when delaying cover crop termination for 2 weeks post cash crop planting as compared to other crops. Corn may more easily be subject to competition, even companion species, when planted green. On the other hand small grains like oats and wheat (winter or spring) can thrive when mixed with a light rate of a clover and/or certain broadleaves when seeded together and you may not have to terminate at all.  

In summary, when cover crops are given a larger window to grow, we can accomplish more of the objective we set out to do. Planting green may be an avenue to fully accomplish the goal of a cover crop and allow for timely planting of the cash crop. However, carefully consider all situations, talk to experienced neighbors and/or trusted advisors, and have a back-up plan in place if you find yourself in one of the contexts described above.