What happens to a corn seed once it’s put in the ground?
At some point, God willing, it’ll break through the surface of the soil and stretch it’s little baby corn leaves in the sun. But what happens in that darkness between planting and emergence? And how? And why? And why should you even care?
This is the time of year when I typically write my it’s-too-early-to-be-late article about planting date. Year after year I’ve encouraged y’all to wait. To stop watching the neighbors. To stop watching the calendar. This year, I’m going to stop telling you though. And let a corn seed show you.
So let’s enter that darkness: a seed is closed into a furrow. The planter rumbles away. Now what?
The first order of business is imbition of water. To germinate, that seed needs to imbibe two times its dry mass in water. If all is well with our newly planted seed, it’ll take 24-48 hours to do that. If, however, something is amiss, it will take longer.
If all is well, our seed is tucked snugly into warm and welcoming soil all around. With good seed-to-soil contact and a suitable temperature, the imbition of water is a relatively short process and after a day or so, germination occurs.
But often, something is amiss.
Perhaps there is poor seed to soil contact, perhaps the result of planting into an overly wet soil that hindered your equipment’s ability to adequately close the furrow. Because of the lack of proper seed-to-soil contact, the seed imbibes water at a slower rate, unable to use its entire surface area, and germination is delayed.
Perhaps the soil is unwelcomingly cool, perhaps the result of planting when air temperatures are too low (take heed: the best planting dates in our area typically fall between April 17-29), or the result of planting into overly wet soil, which warms more slowly than drier soil. Because the cool temperature of the soil doesn’t support speedy biochemical and physical reactions, the imbition of water is slowed, and germination is delayed.
Perhaps the seed is planted too deep, perhaps the result of the settings or errors in the setup of your planter or the result of hastiness in the field or lack of proper downforces which can cause your row units to bounce and sink some seeds too deeply. Whereas a seed planted at a depth of 2 inches requires approximately 125 GDUs to break through the soil surface, a seed planted too deep can require 25-50 more, and germination is delayed.
On the other side of that coin, seeds that are planted too shallow (less than 2 inches) have their own special set of problems as well. Yes, corn planted shallower require less GDUs for emergence, but they are also subject to daily if not hourly changes in both soil temperature and soil moisture. The rate and extent of those changes vary across soil types and tillage systems. That oscillation of wetting and drying, warming and cooling is hard on a seedling trying to start its journey to the soil surface.
Perhaps the conditions are quite good the day of planting, but cooler subsequent days drop the soil temperature. Soil temperature is critical not just at planting but also for the 72 hours that follow it. See the paragraph above re: cool soil. Germination is delayed. Planting into a cool soil that is warming is always better than planting into a warm soil that is cooling.
Much can be amiss in the darkness in the soil, but most can be avoided by attention to conditions. Achieving “all is well” status isn’t so difficult, though it does require a degree of patience that many of us seem to lack. Slow down, friends. Tight margins make this the year to maximize the Net Effective Stand Percentage or NESP. (Take a look at Keith’s article for tips on how to manage for just that.) And know: you do have the time, the equipment, the technology to be tactical. Mistakes made in planting can be exponential and exert a huge effect on the success of your season. Slow down. Find your green light in the soil instead of on the calendar.