Q&A on Planting Cover Crops into Destroyed Seed Corn Fields - UNL CropWatch,

Q&A on Planting Cover Crops into Destroyed Seed Corn Fields - UNL CropWatch,

August 5, 2011

Because of issues with greensnap earlier this summer, some seed corn producers in central Nebraska are faced with having to destroy their fields. One of the management options for these fields is to plant a cover crop. The following questions and answers by extension educators Jim Schneider, Hamilton County, and Mark Hinze, Hall County, are designed to help those seed corn growers who are unfamiliar with but now considering planting cover crops on these acres.

Q:  I already have a "cover crop" of weeds — pigweeds, kochia, lambsquarter, foxtails etc. Why would I want to start over with bare ground and risk getting another crop to come up when I could just leave the weeds in place to hold down the soil and then disk it in the spring before planting a new crop? The weeds will recycle the nutrients and keep the ground from blowing just as well as any blended cover crop!

We need to think about cover crops as “crops.” Crops are planted for a specific purpose and at a specified uniform planting rate to ensure uniform ground cover and performance. The specific purpose may be to recycle nutrients, pulling them from the soil profile and storing them in the biomass for release during the next crop year. All cover crops do this, but the brassica family seems to be the most efficient. Your purpose also might be to fix nitrogen, which means to convert atmospheric nitrogen to the elemental form. Legumes do this. You also may want to create biomass. Grasses with a high carbon to nitrogen ratio would be best for this purpose. Other purposes might include reducing weed competition or interrupting a disease cycle in the field.

The point is that with the correct strategy, destroying the weeds and replacing them with the right cover crop will add value to your system. Leaving the weeds in place will contribute to the intensity of your weedy areas. If you kill the weeds before they set seed, they will serve no purpose other than holding the soil. If you are conscious of the need to hold soil, you might consider continuous no-till. No-till and cover crops work well together.

Q:  I am concerned about weed seed production and control of the existing weeds. How will cover crops do that?

Control the existing stand and then plant a cover crop or cover crop mix to shade the ground and compete against subsequent weed flushes. Some cover crops actually have allelopathic effects. In other words, they exude a chemical which inhibits weed germination. A good example of this is how cereal rye competes against other grass species.

Q. Everyone keeps talking about long-term benefit, but what are the short-term benefits?

Short-term benefits come in several forms. One is weed competition, as was discussed in the previous question. Another may be in the breakup of hard pan layers with deep tap-rooted crops such as tillage radishes. These are measured with observation and a little labor with a tile spade.

Nutrient recycling and nitrogen fixation are other short-term benefits. To test for nitrogen take soil samples at 0-12 inches and 12-24 inches at planting and again just prior to planting next year’s commodity crop. Around the time of the killing frost, cut the above ground biomass (greens) from a given area and submit it to a laboratory for nutrient analysis. A 3-by-3-foot area seems to be manageable and should fit in a large paper lawn and leaf bag. If you are a livestock producer, you might consider running an NIR analysis to determine feed values and minerals.

Q. How am I going to come up with another $30 to $50 an acre for cover crop seed?

The same way you come up with your other crop inputs. You need to decide whether you are looking at this as an investment or an expense. Consider the value that can be gained from planting the cover crop and compare it to the cost of alternative practices such as more herbicide passes, more tillage, or just letting the weeds grow and contributing to the seed bank. You may find that cover crop seed is not as expensive as you think. When comparing, do consider the seeding cost and, if necessary, the cost for termination.

Q: Who has enough seed to get a cover crop established?

There are several reliable cover crop seed vendors in Nebraska.

Q: At this time I really do not care about water use efficiencies as my weeds are covering my ground and recycling the nutrients anyway!

See the first question.

Q: What about my layby herbicide program? The acetochlor, metolachlor, and/or other herbicides (Pendulum) could possibly prevent a cover crop from germinating and/or growing.

This is a valid concern. You will need to review your product label regarding replant options and rotation restrictions. The 2011 UNL Guide for Weed Management (EC130) has a section on "Replant Options and Rotation Restrictions" which starts on page 156. It is likely that you will not find all of the cover crop options listed so you may have to make a judgment call and may want to contact the herbicide company representative. Soil organic matter, soil pH, moisture received since application, and temperature all can have an impact on the life of the herbicide. Look at the weeds present or not present to see if they give you a clue. If possible, hand seed a small area prior to planting the entire field to make a visual evaluation.

Q. What about the herbicide labels and growing a grazing cover crop? Are there restrictions?

There may be. Again, check your label.

Q: What about growing Sudex. Will it too turn into weed seed production that I will have to worry about the following years? As far as that goes, all blended cover crops could become weeds in the future. What guarantee do I have that I won’t be introducing another weed into my seed corn production system?

That depends on how you manage it. If you graze it, this should keep the seed production to a minimum. However the crop carries the risk of prussic acid and nitrate poisoning so feeding will have to be managed carefully. (See the following question about oats for more on the nitrate issue.) Any crop that produces a physiologically mature seed prior to a killing frost can be considered a weed for next year. Some cover crops such as hairy vetch are quite winter hardy and will probably resume growth the next spring. Also, cereal rye is a winter crop so you will need to kill it in the spring. You need to evaluate the growth cycle of the cover crop and have a termination plan in mind if you need it.

Q: I've heard of some trying to grow Oats for grazing or for baling. Will there be chemical restrictions in the hay quality?

Here again, refer to the product label. The 2011 Guide for Weed Management has a section called “Crop Growth Stage Limits and Preharvest Intervals for Herbicide Application” on page 155. Nitrates may be a larger concern. High soil N levels can create toxic levels in the oats intended for haying or grazing. Before planting the cover crop take a 0 to 24 inch soil sample for analysis. A general rule is to not graze or hay the crop if the soil nitrate level is 100 lb/ac or more.

Q: Will my insurance become nullified if I grow a crop to graze and/or bale?

You need to check with your insurance agency before destroying your current crop or planting a cover crop. In speaking with a representative of one insurance company (Babel Crop Insurance, Wood River), he advised that as long as the seed crop loss occurred late enough in the growing season so that replanting wasn’t feasible, a producer may plant a cover crop in the affected area. Prior to planting a cover crop, a multi-peril crop insurance adjuster must complete an appraisal and provide permission. Check with your insurance provided regarding haying or grazing of the cover crop.

Another consideration relates to insuring the crop after the cover crop. According to Corey Brubaker, state conservation agronomist with NRCS, if it is irrigated acreage, there are no restrictions with regard to cover crops.  If it is non-irrigated acreage, the producer needs to be mindful of the current double crop statement:

"Insurance shall not attach or be considered to have attached on any non-irrigated acreage planted following another crop in the same calendar year if: 1) a perennial hay crop was harvested; or 2) another crop has reached the headed or budded stage (regardless of the percentage of plants that reached the headed or budded stage) and/or that has been harvested in the same calendar year.”

Brubaker said that as a general rule if the cover crops planted will freeze out this fall or winter, there shouldn’t be a problem with insurance. If the cover crop overwinters. it will probably need to terminated by mid-April. The exact date is still being determined. When this date is determined, it will be identified in a special insurance provision. Your crop insurance agent will have that information when it becomes available.

Jim Schneider
Extension Educator in Hamilton County
Mark Hinze
Extension Educator in Hall County