Parts of Illinois received some precipitation for the third Sunday in a row (starting with Easter) on April 15, and in a few places, also for the third Sunday in a row, it came partly in the form of snow. That streak should end this weekend, and less rain and warmer temperatures are predicted to move in for the rest of April.
Some ammonia went on late last week and there was planting activity in places, but NASS reported no (meaning less than 1% ) of the corn or soybean crop planted by April 15. It rained again over much of Illinois on April 13-15, and cool temperatures and slow drying of soils continue to delay the start of planting.
One concern when corn is planted into cool soils is the uptake of cold water as germination begins. When the first water moving into a dry seed is at a temperature below the mid-40s, “imbibitional chilling injury” (ICI) can result. Rain and lower air temperatures that followed planting in some fields on April 13 or 14, such injury is a possibility. We expect to see such damage more often than we actually see it, but low-moisture seed takes up (cold) water quickly, and moisture of planted seed planting might influence the amount of damage. If seed has a chance to take up warmer water before cold rain comes, such damage will probably no occur. Cold water makes membranes in the seed more brittle, and can cause cell death.
ICI damage usually shows up as abnormal seedling growth, often with “corkscrew” roots and shoots. The practical effect of this is that it lowers emergence. Unlike death of seeds from lack of oxygen, which was widespread following heavy rainfall after planting in 2017, ICI symptoms aren’t necessarily more common in low-lying parts of a field. There’s no fix for ICI – if it lowers stands enough, replanting may be necessary. But if affected seedlings are able to emerge, they may develop normally.
Almost every year in some part of Illinois, corn is planted into good soil conditions, but then it rains and turns colder, causing emergence problems. People tend to remember this as a “window” during which they should have held off planting until the forecast was more favorable. Such hindsight is usually good, but it’s rarely the case that the forecast is so accurate that waiting to plant, at least after the third week of April, turns out to be the best decision.
At the same time, as long as soil and air temperatures remain cool, the early-planting advantage will be smaller than usual this year. It takes about 115 growing degree days from planting to corn emergence. Fewer than half that many GDD have accumulated since April 1 in most of Illinois, and with daily accumulations in single digits this week (a low of 50 or less and a high of 60 degrees provides only 5 GDD), planted corn isn’t growing a lot faster than corn seed still stored in the shed.
While cool temperatures have slowed surface drying, April rainfall, with the exception of a number of counties in east central Illinois, has been at or below normal to date. That has allowed excess water to move out of surface soils, and once the weather starts to warm, the surface soil will start to dry and conditions for planting will improve quickly. We need to wait until the seedbed is in good condition, but if predictions hold, we could see planting begin by this weekend, and accelerate next week. There’s no great advantage to planting on April 30 instead of May 1, but a strong start to planting as April ends will do a lot to restore our hopes that the 2018 season will be a good one.
If we can plant either corn or soybean, next week, which crop do we start with? If two planters can run at the same time, “both” would be a good answer. If it has to be one or the other, I’d still give a small edge to corn, only because it can emerge a little more consistently than soybeans if plant into cool soils. If we don’t get heavy rainfall before emergence, though, both crops should get off to a good, albeit somewhat delayed, start.
Since my article last week in which I mentioned that some people had planted soybeans very early (mostly in mid-March) this year, I’ve received several more reports, some indicating that hundreds of acres of soybeans were planted that early. If any of those fields establish good stands, please let me know and we can record this as the miracle it would be. I also saw in the recent newsletter from the Illinois Crop Improvement Association that both warm and cold germination percentages of soybean seed are not as high this year as they were last year.
If soybean planting (and replanting) is into cool soils, it might be worthwhile to bump up seeding rates to account for the possibility of lower germination. If you know the cold score, you might consider dividing the desired plant population (say 115,000 per acre) by the cold score minus 5 points to give seeding rate; as an example, if the cold score is 85%, divide 115,000 by 0.85 – 0.05 = 0.8 to give a seeding rate of about 144,000. If a cold score isn’t available, divide by warm germination minus 10 instead. If planting into warm soils, divide by the warm germination minus 5 points to make the adjustment.