C.O.R.N. Newsletter: 2021-05

With melted snow and warmer weather in the forecast, is it time to apply nitrogen to wheat?

The short answer. Wait until green-up to apply N to wheat.

The long answer. Wheat does not require large amounts of N until stem elongation/jointing (Feekes Growth Stage 6), which is generally the middle or the end of April depending on the location in the state and spring temperature. Ohio research has shown no yield benefit from N applications made prior to this time. Soil organic matter and/or N applied at planting generally provide sufficient N for early growth until stem elongation.

Nitrogen applied prior to rapid uptake by the plant has the potential to be lost and unavailable for the crop. Nitrogen source will also affect the potential for loss. Urea-ammonium nitrate (28%) has the greatest potential for loss, ammonium sulfate the least, and urea would be somewhere between the two other sources.

Ohio research has shown that yield losses may occur from N applied prior to green-up regardless of the N source. The level of loss depends on the year (losses are smaller if the ground is not frozen or snow/ice covered). This same research did not observe a yield increase from applications made prior to green-up compared to green-up or Feekes Growth Stage 6 applications. Keep in mind that green-up is a descriptive, relative term and not a definable growth stage. Our definition of green-up is when the new growth of spring has covered the dead tissue from winter giving the field a solid green color- thus, growing plants.

There is a legitimate concern that wet weather may prevent application of N at early stem elongation. Ohio research has shown a yield decrease may occur when N application is delayed until Feekes Growth Stage 9 (flag leaf fully emerged). Thus, a practical comprise is to topdress N at any time fields are suitable for application after initial green-up to early stem elongation. There is still a potential for loss even at green-up applications. To lessen this risk a producer may want to use a N source that has a lower potential for loss such as urea or ammonium sulfate. ESN (polymer-coated urea) is another option but it needs to be blended with urea or ammonium sulfate to ensure enough N will be available for the crop between Feekes Growth Stage 6-9. The source of N becomes less important as the application date approaches stem elongation. The percentage of urea and/or ammonium sulfate would need to be increased with ESN for application times closer to Feekes Growth Stage 6. A producer may want to consider the use of a urease inhibitor with urea if conditions are favorable for volatilization losses: warming temperatures, drying winds and no rain in the forecast for 48 hours.

A split application of N may also be used to spread the risk of N loss and to improve N efficiency; however, Ohio State University research has not shown a yield increase from this practice compared to a single application after green-up. In a split system, the first application should be applied no sooner than green-up. A small rate should be applied with the first application since little is needed by the crop at that time and the larger rate applied closer to Feekes Growth Stage 6.

In summary, a producer may get away with applying N prior to green-up on wheat. However, university data has not shown a yield advantage for these early applications, but results have shown in certain years a major N loss and yield reduction from applications prior to green-up. Why take the risk? Just wait until green-up; the wheat does not need most of the N until April and May anyway.

We are at the point of the winter that daily average temperatures are rising and the days are getting noticeably longer. This freezing and thawing over the next few weeks is what gives frost seeding a great chance to work.

Frost seeding is a very low cost, higher risk way to establish new forages in existing fields by spreading seed over the field and let the freezing and thawing action of the soil allow the seed to make “seed to soil” contact allowing it to successfully germinate. When you see soils “honeycombed” in the morning from a hard frost, or heaved up from a frost, seed that was spread on that soil has a great chance to make a seed to soil contact when the soil thaws. I think the two biggest reasons why frost seeding fails is people wait too late to frost seed and the seed never makes good contact with the soil. Let’s face it, if the seed does not land on the soil but on existing living or dead vegetation, it does not have a chance to successfully germinate: you need exposed soil that should be present in a fall planted small grain field.

Time is short to assess and seed potential fields. We are rapidly running out of time for a likely successful seeding, so start as soon as possible. Typically you can start at the beginning of February through mid-March. My opinion is that once we get into March, the chance of success starts to drop.

The age old question is what to plant. The seed that has the best chance to germinate and become established is red clover. For years I recommended medium red clover but I am now convinced that that no matter what we plant, use improved varieties, unless the planting is only for a temporary cover. Advancement in genetics is amazing. Numerous studies confirm that those varieties will last several years longer in most conditions. Forage trials at OSU show there a several red clover varieties that have high yields and stand percentages 60% or greater after four years. These are more expensive varieties than some of the common, shorter-lived varieties, but I think it is worth it.

Red clover is a heavy round seed that has a better chance of making soil contact then a light flatter seed.  Dr. Garry Lacefield, retired Extension Forage Specialist from University of Kentucky says that clovers, seeded in the right conditions will germinate most years. Grasses are more “hit or miss” germinating about half of the time. With alfalfa, the odds are even less. Frost seeding alfalfa into an alfalfa stand rarely works as existing alfalfa is toxic to new plants. If an alfalfa field is starting to thin out, an option to extend the life of the stand would be to frost seed red clover.

  Another reason to plant clover, especially red clover is the high seedling vigor. It is tolerant of a wide range of soil pH and fertility conditions and is more drought tolerant than white clover. The advantage of frost seeding a legume like red clover is that legumes “fix” nitrogen typically in excess of their own needs, providing added fertility to other plants, improving an improved stand. Once legumes become established in a stand of grass and compose 25-30 % of the stand, there is no need to provide additional nitrogen, reducing fertility costs.   

If you choose to frost seed grass, which will do best? Studies by Dan Undersander, Forage Specialist from University of Wisconsin indicate that perennial ryegrass will do best (note that it grows best in Ohio north of I-70), followed by orchardgrass, then timothy. Other studies note that annual ryegrass will work good compared to other grasses.

Some other tips to help succeed include mixing with granular fertilizer when you spread the seed. The coarse fertilizer, when mixed with clover seed will “scour” the seed coat and help in germination. Keep in mind that when you use a broadcast spreader, the fertilizer will travel twice as far as seed, so plan accordingly unless you want a striped field of clover. Over the years, I have heard people applying anywhere from 2-10 pounds of seed per acre with the lower amount applied on permanent vegetation and likely the higher rate on small grain fields. If your small grain fields still have exposed soils and you get several frosts after broadcasting, I like your odds of a successful frost seeding.