Published Jun 26, 2016

Is an oat cover crop the market we need to diversify the landscape?

By Sarah Carlson

Oat cover crop seeded Sept 2015 near Knoxville, IA. Picture taken Dec 16, 2015.

Growing third crops in Iowa is of interest to many farmers but lack of obvious markets can reduce farmers’ enthusiasm about these soil building crops. Cover Croppers are using spring small grains, like oats, as fall cover crops sometimes mixed with cereal rye. Spring small grains seeded in the fall prior to September 20th in central Iowa can provide a lush, green burst of cover crop at harvest. Cattlemen like oats mixed with cereal rye to get some fall grazing too. But Cover Croppers comment that oats can be “finicky” and more delicate to establish than cereal rye. I asked the PFI Cover Crops discussion list what observations they had from aerial seeding or early fall direct seeding spring small grains like oats as cover crops. Could a new potential oat market be right in front of us or are oats to inconsistent for Cover Croppers to want to use? For example if oats were seeded as part of a cover crop mix on 10 million acres (the number of acres needed to meet Iowa’s Nutrient Reduction Strategy goals) we’d need about 125,000 acres to grow that seed. If cereal rye was a part of that mix we’d need about 285,000 acres to grow that seed. Total small grain acres in Iowa today is 100,000 and of that 55,000 is oats.

Cover Croppers on PFI’s Cover Crop email discussion list said this about oats:

—If the oats are not incorporated, they may need a couple of shots of rain to get going. One good rainfall event is enough for germination, but if they are exposed to the sun for very long (leaf drop is inconsistent), or the soil moisture is low, it won’t be enough to keep them alive. Had that happen in ’14 to me; lots of bare spots at harvest. I’m also looking at doing 1bu oats with 2bu rye in the fall this year. Could be good, could be bad. Long time till then!

—I had flown on something like that [oats+rye] into corn that was rotating to soybeans the following year.  The seed survived lying on the ground for a month, and I was able to harvest the corn just before a good rain in mid October.  With all the residue protecting the seedlings from drying out, yet able to get sunlight right away, it worked out.  Lucky, I’m sure, but it made me wonder if blowing cover crop seeds under the corn head as we harvest would work most years.  No seed to soil contact, though, so I just have not invested in the idea. I used to blow soybeans in with a Hiniker cultivator, so I would mount a seed spreader like that under each snout (pointed forward onto “bare” earth) and run the hoses back along the feeder house to a Gandy somewhere on the combine.  GPS driven electric drives maybe.

In my experience with aerial seeding, I’d much prefer to see spring barley used over oats. The spring barley will give a nice green up in the fall and seems to tolerate the lack of seed to soil contact better than oats. My cows don’t seem to care if they’re eating barley or oats. The seed cost per pound is similar, but there are more barley seeds in a pound so I can use a bit lower rate. Pilots also appreciate having a seed mix that spreads evenly and uses more dense seed. Oats fall short in both of those categories. If the overseeding is done by a Hagie-type ground rig, I’d be less concerned about the spreading and seed density.

Tom Kaspar from ARS who has researched cover crops in Iowa for several decades made these comments.

I did most of my trials with an oat-rye mix very early in my days of working with cover crops when we were still novices and we would undoubtedly be more successful today.  That being said I am not sure that we have oats as a cover crop or the oat-rye mixture completely figured out.  But I will give you some thoughts.

  • The biggest thing is that a bushel of oats (32 lbs) has a lot less seeds than a bushel of rye (56 lbs).  Seed size also varies a lot both in terms of seeds/lb and seeds/volume.  Oats have a relatively low seeds/vol or density.  So the biggest thing is to consider the number of seeds rather than weight. Secondly, nobody knows the “right” mixture of oat and rye. 50:50 based on seed number is probably OK but I might bump that up to 60:40 oats to rye.  Probably varies by year and purpose. Soil moisture helps, but temperature, wind, radiation, canopy cover, surface roughness and residue cover play a part.  As I say below it “seems” that rye germinates better on the soil surface.
  • Oats or an oat-rye mix needs to planted or seeded pretty early to grow very much in most years (except last year of course).  In central Iowa we like to have oats seeded by mid Sept. and if we are lucky they will grow until early Nov and maybe a bit later.  So in most years and with most soybean maturity groups there is little opportunity to seed/plant oats early enough at or after soybean harvest either with a drill or with some spreader with the combine.  So instead we usually plan to overseed oats in late Aug if we can, depending on year, weather, crop maturity, and moisture conditions.  In some ways a soybean canopy can help shade oats and the soil surface to keep soil surface moist to get them started, if it rains, and we are more “likely” based on climate records to get rain in late Aug than Sept.
  • Oats will work pretty well with overseeding or aerial seeding, but for some reason not quite as well as winter rye or winter wheat.  I am guessing it is because of the oat hull and/or somewhat larger seed size of oats.  As a result they seem to need more rain/soil moisture to germinate than rye or wheat and don’t work/settle into residue as well as rye or wheat do.  Some people have used or considered using spring barley or spring wheat for that reason.  A way to work around this issue is to use a higher seeding rate and/or to devise a way to incorporate the seed when overseeding.  We have incorporated oats that were overseeded into soybean in late August using wheel shields and adapting an old cultivator and this worked really well.  Soybean have to be an upright variety and obviously there are some years where this could not be done until the soybean begin to drop leaves and standup better.  Another comment about oats is that pilots aerial seeding them don’t like oats because their volume to number of seeds ratio is not very good and it takes more refilling to seed oats with a plane.  Same would be true for hoppers on ground based equipment.
  • Oats planted/seeded early will grow better than winter rye in the fall, but planted after a “certain date” (depending on the year) winter rye will grow better than oats.  Basically oats grow better than rye in warmer weather and are not restricting shoot growth to survive the winter.  On the other hand, rye grows better at cooler temperatures and survives frosts much better than oats, so sometimes rye grows better.  So this brings up the oat-rye mixture.  If planted early enough a mixture of oats and rye will produce nearly as much as a sole-crop winter rye in the spring because of tillering by the winter rye.  The advantage comes from more oat growth in the fall.  The trick is we don’t know what the right ratio in a mixture would be.  I suspect it would vary depending on the year a bit.

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