As the snow melts from croplands and early spring warmth results in perennial plants coming out of dormancy, walk your fields to check crop condition. We expect – and certainly hope – that conditions this spring will be better than they were a year ago, when there was significant winter damage to alfalfa and some forage grasses including orchardgrass and tall fescue.
It was the first time since tall fescue became a popular forage grass in the Northeast that we saw significant damage, so I’m optimistic that this might turn out to be a rare event. However, you won’t know unless you get out there and walk your fields – a “windshield appraisal” isn’t good enough. Determining the status of the forage in each field on your farm is important because it gives you time to create a Plan B if you find problems.
Winter damage is rarely uniform across a field. Sometimes the low areas are hardest hit, while in other cases the worst damage is on the knolls and other high areas. Winter damage in high areas may be because the snow blew off, exposing the plants to subzero temperatures. A few inches of snow provides a surprising amount of cold weather protection, which is why agronomists recommend that farmers leave 5-6 inches of stubble during fall harvest of alfalfa and alfalfa grass.
Planning spring fertilizer applications
If you grow straight grass or alfalfa grass you should plan applications of nitrogen fertilizer or manure. Manure is usually the cheapest alternative since you need to spread it anyway. However, heavy manure spreaders and soft early-season field conditions are a poor match, so commercial nitrogen (N) is often best in the early season. Urea is typically the cheapest source of N and if applied in early spring when the soil is still cool, volatilization losses should be low. A 50-50 blend of urea and ammonium sulfate is also a good choice, especially where manure hasn’t been applied in recent years. Forages need sulfur, something precipitation used to supply but because of reduced industrial emissions this is no longer the case. If you don’t apply either manure or commercial nitrogen, yield and crude protein will suffer so much that some agronomists question if it’s economical to harvest the crop at all.
Grass fields are simple: Apply some source of N and if you don’t apply manure prior to first cut then apply it sometime during the summer. In many cases, a single annual application of manure maintains adequate phosphorus and potassium levels, but do a soil analyses to be sure. Fertilizing stands containing both alfalfa and grass isn’t quite as simple. Alfalfa grass stands with at least two-thirds alfalfa will supply enough nitrogen to the grass that supplemental N isn’t recommended. However, as the percentage of the alfalfa declines, at some point the field should be treated as if it was a grass field (though perhaps not using as high a rate of N as with straight grass). At Miner Institute, our practice is to apply commercial N to alfalfa grass stands when the proportion of alfalfa falls to less than 50 percent, using about half the N rate we do for straight grass. Nitrogen doesn’t hurt the alfalfa but increases the yield and protein content of the grass. This is true regardless of the species of grass you seeded with the alfalfa.
Is this trip necessary?
In most cases you decided on your crop rotation last fall – which fields will be rotated from corn to hay crops and which hay fields will be planted to corn (or another row crop such as soybeans). However, winterkill can cause a change in plans, especially when it hits your best alfalfa fields. If alfalfa winterkill is in an alfalfa grass field that going into last fall was at least 50 percent grass, the field can still be salvaged by a timely application of nitrogen or manure. However, if the field was almost entirely alfalfa, there isn’t enough grass to make N application economical.
Yield potential is more reliant on alfalfa stems per square foot rather than alfalfa plants per square foot. A stem density of 55 per square foot is very good, while any field with an average of less than 40 stems per square foot is a candidate for rotation to a different crop.
That’s true for alfalfa, but what about alfalfa-grass? This is a much more difficult assessment because it can be affected by the species of grass – and therefore the yield potential. Rules of thumb are few and far between, so walk the field to determine how uniform winter damage is and what proportion of the alfalfa is still OK. Wait until the spring growth on alfalfa is 3-4 inches high since some plants that were injured may be slow starters. The more grass you have in the field, especially aggressive species such as orchardgrass and tall fescue, the more alfalfa winterkill you can tolerate and still expect reasonable yields.
They say the proof is in the pudding, but in this case the proof is in the first cut yield. If yield turns out to be disappointing, it’s not too late to rotate the field to corn. There are some very good short-season corn hybrids that produce excellent yields, especially if planted at a moderately high population. A summer annual such as BMR sudan-sorghum is another alternative, but if you plant the corn by early June my recommendation is corn. However, nothing is simple: The recommendation for spring management of a winter-damaged alfalfa field where the plants have been injured but not killed is to not to harvest it too early, allowing for plenty of root carbohydrate recovery. But these are the very fields you’ll want to harvest early enough to allow timely planting of corn in the event that yields turn out to be disappointing. No one said farming was easy. Good luck!