Let it snow (or freeze, at least)
Dormant seeding requires a little gambling with nature.

By Genevieve Slocum

editor's NOTE:

This season our interns took turns tracking their observations and sharing what they were learning as they helped out the various departments here at The Rodale Institute.

This next generation of farmers offered insights into what motivates them to go against the tide when so many farm families struggle to keep up-and-coming generations interested in farming.

As the season turns colder, most of our interns have left us for greener pastures. Genevieve Slocum is staying on a little while longer and will continue sharing her experiences here in Intern Journals.

--NF Editors

Posted January 12, 2007: Dormant seeding is a practice that perhaps few people in Pennsylvania (and states south) have heard of, which may be why our first reaction is commonly that it’s completely off the wall. The practice is more widespread among conventional farmers in places like North Dakota (and throughout the upper Midwest), where farmers have to get creative in order to maximize their returns from the short growing season. It is in many ways ideally suited to colder climates, but there is no reason why it cannot be tweaked and adapted for inclusion in the cover crop experiments here at The Rodale Institute.

Basically, dormant seeding involves planting just before the soil freezes, with the hope that the soil temperatures stay cold enough throughout the winter that the seed does not germinate until the weather gets consistently warm enough in the spring to foster germination and steady growth. Obviously, this is a huge gamble, and an especially precarious one in the very late fall and early spring.

The farmer has to be willing to bet that soil temperatures will be consistently cold enough from the planting date on throughout the winter to inhibit germination, and then that they’ll be consistently warm enough following the first major ground thaw to support the rapid growth that many crops put on in the early spring. In fact, in the case of a winter annual cover crop like hairy vetch, the farmer will rely heavily on this rapid growth to compensate for the early fall growth he has missed, so many growing conditions have to line up pretty nicely to ensure success.

Dormant seeding is in these respects like any cultural practice, involving a lot of risk and delicate timing, but North Dakota is a great place to try it. Its consistently cold temperatures and fairly dependable winter snow cover keep the ground cold and the cold sealed in. Snow-insulated soil is less subject to dramatic variances in temperature, which would either initiate germination and then promptly kill the seedling, or force the buried seed up out of the ground through the heaving action of freeze and thaw cycles. The ideal conditions would be to have continuous snow cover throughout the winter, with soil temperatures never reaching above 35°F (this is about the threshold below which the seed’s metabolic activity dips to a minimum, and where little moisture is available for it to imbibe). The top two inches of soil should be near or below 32°F. Dormant seeding must take place in the window of time between the onset of freezing temperatures and the first snow.

In North Dakota, where the practice is used mostly on canola and spring wheat, dormant seeding may actually be used to diversify the flowering dates, much the same way that intercropping is used to deal with pests. If the crop is broken down into different stages of maturity, then the entire crop would not be wiped out by hot, dry spells or other harsh conditions (drought tolerance varies at different stages of development). It also sometimes helps to get the crop established before the springtime emergence of predators like the flea beetle. Again, these benefits have to be carefully weighed against the risks and guesses involved.

Whether in the Midwest or in Pennsylvania, dormant seeding works better if it can be done into residue. Ground covered with stubble or other crop/weed residue is much better insulated and can magnify the soil’s already buffering effects against the variances in ambient temperature. A more consistent stand results in the no-till or minimum-till systems because the protective layer of residue that provides insulation and shelter is left undisturbed.

The real challenge in adapting dormant seeding for a cover crop is that it has traditionally been used not as a last resort for a winter annual, but as a head-start for a spring crop such as spring wheat. Farmers in the upper Midwest typically take this chance with dormant seeding not out of desperation, but to save time and spread out labor on spring planting and to beat unpredictable spring weather conditions.

At The Rodale Institute, we are currently experimenting with dormant seeding hairy vetch, a winter annual legume cover crop, and now whether dormant seeding can be adapted to it. We have typically planted it 40 to 50 days before the first killing frost (mid-August to mid-September in Kutztown, Pennsylvania), which gives it time to establish root and plant growth before winter dormancy. It then blooms in the spring and can be rolled or plowed under. If the farmer misses the critical window of time for a fall planting of hairy vetch, the hypothesis is that he could fall back on dormant seeding.

In our dormant seeding trials, hairy vetch was no-till drilled into four treatments: 1) dead berseem clover/weed residue; 2) dead annual sweet clover/weed residue; 3) heavy residue of dead (August-planted) spring oats; and 4) a clean-till field with an established cover crop of cereal rye. These December 20 plantings will be compared with an August 1 planting, a September 1 planting and a spring 2007 planting. The amount of biomass put on in the fall has not shown to be a good predictor of spring biomass or of flowering date but will tell us much more about the optimum planting date to minimize winter kill.

Since dormant seeding for a winter annual is pretty much unheard of, this trial may also answer some major questions about the need for vernalization of a winter annual. Vernalization is a hormonal response to temperature; winter annuals generally require a cold spell in order to enter a reproductive stage and flower. Dormant-seeded hairy vetch may be able to get some of this cold exposure during its early growth in the spring, but the plant itself will not undergo a stage of dormancy. If it can survive these abnormal conditions, the next question is whether its growth in the spring will be quick enough to catch up with its fall-planted counterparts so that it may be rolled in time for a no-till corn planting, or at least to have enough biomass to be plowed under for nitrogen.

Trying to dormant seed winter annuals in a warmer climate (a technique originally designed for spring grains in a much colder climate) is one manifestation of learning how to adapt similar methods to very different environments, and to tailor agronomic principles to the geography of our locale. Rather than a one-size-fits-all approach, i.e. chemical application, organic farmers are forced to build a consciousness about their land’s individuality and perhaps learn more about their own soil conditions.

Our climate is much less predictable than a more northern climate (in general but especially this winter), and the adaptation of dormant seeding in Pennsylvania requires a lot of soil scrutiny in terms of temperature, composition, drainage, etc. The important thing is to build diversity of technique and to have as many “rescue” routes for a farmer to fall back on as possible.

So far, dormant seeding a hairy vetch cover crop is pure speculation but may be perfected over several winters of trial and error.