Planting Cover Crops
Usually, the most consistent cover crop stand is obtained by using either a no-till or a conventional drill. Conventional drills are designed to plant into a prepared seedbed. No-till drills have a coulter in front of the openers to slice through crop residue. There are many different manufacturers and ways to set up your drill. You should be familiar with the operator’s manual for your particular drill. A good introduction to grain drills and planters can be found here.
The first thing to do is check the seed boxes and drop tubes. Spiders particularly love to build webs in drop tubes and will clog them up. Use an air compressor to blow the tubes out and a flexible wire to make sure they are clear. Planting a field to find missing rows is a frustrating experience.
No-till drill.
The drill should have rate charts for settings to obtain a particular seeding rate. Some charts are on the seed boxes, others are found in the operator’s manual. These charts are a good guide but because seed sizes vary considerably even within a particular species, the drill should be calibrated to make sure you are planting the right amount of seed without planting too much. Calibration is not difficult. There are a number of methods, but here is a simple and accurate method that will work for no-till and conventional drills.
As you are calibrating the drill check to see that seed is dropping from all tubes, there is proper seed depth, and the furrow is being closed. Walk behind the drill to check that seed is dropping from all the tubes.
For specific cover crops, seed depths are often given as a range such as ½ to 1 inch. The seeds need to be at the right depth but not too deep. Seed placement may also depend on soil moisture conditions and the forecasted weather. In some cases, the seed should be placed a little deeper to take advantage of soil moisture below a dry surface layer. In wetter conditions, the seed may be placed towards the shallower end of the range.
Seed depth will be set on the drill by adjusting the downpressure, the gauge wheels (if these are present) or the press wheels, depending on the drill. A good rule of thumb is that the furrow opener moves through the soil at twice the desired seed depth. For example, if the seed should be planted at ¼ inch, the opener should be set to ½ inch. There is a limit to this. Most drills will not open deeper than 2 inches depending on the soil type and condition.
Some small seeded cover crops like clover need to be planted very shallow. A small seed box is needed to get these seeds metered out properly. Getting the right depth for small seeds like clover may be particularly difficult with heavier no-till drills. In many cases, tubes from the small seed box can be pulled out to drop the seed on the surface just before the press wheel to keep the seed shallow.
Check the planting depth by inspecting the furrow and digging down a short distance to find the seed. One trick to help you find seed that isn’t inoculated or coated, is to very lightly spray paint seed spread out on a plastic tarp or newspaper. A light coat of orange or red color will make the seeds much easier to find. You should lightly coat enough seed to fill all the cups in the seed box. It doesn’t take much. A heavy coat of spray paint will gum everything up.
After calibration, make sure all the seed tubes are reattached. Once you are ready to plant, remember to check the seed boxes to ensure these are full. It’s always a good idea to check the drive mechanism and seed boxes periodically while you plant.
A note on cover crop mixtures. Some farmers are using mixtures with as many as eight to ten cover crop species with the goal of increasing biodiversity and increasing soil health. These mixtures often contain a wide range of seed sizes. There seems to be two schools of thought in terms of drilling these mixtures. Some farmers mix all the seeds into the large seed boxes and plant. Others put small seeded legumes and brassicas in the small seed box and the larger grain seeds in the large seed box. Both methods can work.
Many farmers broadcast cover crop seeds to help them cover large acreage in a relatively short period of time during the busy harvest season. Broadcasting also can help get cover crops planted earlier than if the producer waited until after harvest to drill. Broadcasting cover crop seeds can work if there is sufficient moisture. Residue from previous cover crops or cash crops can improve germination. Seeding rates should be increased by 20 to 50%. This approach is much more effective with very small seeds (e.g. clover) than with very large (e.g. faba bean).
Spreaders can be mounted onto ATVs, tractors, high boy sprayers or other equipment to broadcast the seed. Some farmers mix the cover crop seed into lime or fertilizers and apply in one pass. However, many fertilizers will cause ‘salt burn’ that damages or otherwise renders seed non-viable. Care should be taken to avoid this outcome. Others mount spin spreaders to high boy sprayers and broadcast cover crop seeds while spraying.
Just like the drill, the spreader should be calibrated and you should know how wide a swath the spreader will cover and the spread pattern. Information on calibrating a bulk dry fertilizer spreader can be found here. The method can be adapted for mounted spreaders.
There are several windows when cover crops can be broadcast in the Coastal Plain. These include:
- Before digging and harvesting peanuts. This options usually gives a good cover crop stand, but can be problematic if there are wet conditions that cause the cover crop to germinate in between digging and harvest.
- After digging and before harvesting peanuts.
- After peanut harvest.
- Before cotton defoliation. This option has worked well for producers and generally produced adequate cover crop stands.
- After cotton harvest before mowing stalks
- Before soybean leaf drop.
- After corn harvest. This can be problematic during dry conditions due to the heavy corn residue.
Aerial seeding can be an option for grain cover crops like cereal rye. These can generally germinate on the surface and have their roots penetrate into the soil if sufficient moisture is available. Brassicas can also be successfully aerially seeded. Legumes typically need better seed/soil contact and can be less successful. This is particularly true for large-seeded legumes like Austrian Winter peas or lupins. Aerial seeding should be done when there is good moisture in the top inch of soil or before a predicted rain. Producers report more success with pilots who have experience with aerial seeding. Pilots should calibrate their aerial applicator. Planting windows are similar to those listed above for broadcasting, except cover crop can be aerial seeded into corn after it has senesced at least up to the ear.
Contributors:
Ronnie Barentie, Dooly County Extension; Julia Gaskin, Extension Specialist, University of Georgia; Dr. Jake Mowrer, Extension Specialist, Texas A&M