Issue No. 24, Article 7/November 6, 2009
Late Harvest Issues
Corn harvest continues at a snail's pace in Illinois, with only 19% of the crop harvested by November 1. October was a very wet month, and the cool temperatures resulted in very slow drying, even if the crop reached physiological maturity earlier in the month. There are some fields in northern Illinois where the season ended prematurely with freezing and loss of leaf area, in some cases when the grain was still at or above 40% moisture.
Can we wait for grain to dry down? Because warm air can hold so much more water vapor than cold air, it is impossible to get rapid drying of grain in the field unless temperatures are in the 70s and 80s after the grain reaches maturity. In 2009, some two-thirds of the Illinois corn crop reached maturity after the end of September, and temperatures during most of October have been below normal. So there has been no rapid dry-down period for most of the crop. By the end of October, average daytime high temperatures have dropped into the 50s over most of the state, and the chance of having even a few warm days with good drying conditions diminishes rapidly. So while we can wait until grain dries down some, we would expect on average for grain moisture to change very slowly in November. Expecting it to drop by as much as a point per week is optimistic.
Why has grain been so slow to dry down? Most of the slowness has resulted from the late maturity of the crop followed by the cool, cloudy, rainy, and humid weather since maturity. And while kernel size may be good, most kernels reached their maximum dry weight under cool conditions or prematurely, which we think tends to make the grain dry more slowly. Ears in some cases have remained upright, helping to trap water. Cobs have generally been wetter than grain, which means slower grain drying.
What about test weight? One of the issues in 2009 is the low test weights being recorded in many parts of the state, in some cases leading to dockage. Number 2 yellow dent corn has a minimum test weight of 54 pounds/bushel, and there are many reports that test weights of high-moisture corn are in the low 50s or upper 40s. It appears that most corn has test weight measured "as is," without adjustment for its high moisture content. We took test weights on some high-moisture samples this fall, before and after drying; in most cases test weights rose by 2 to 4 pounds during drying.
There were some exceptions, however: one sample tested by Lyle Paul at DeKalb was of corn that had not finished filling, and test weight actually dropped to below 50 pounds/bushel when it was dried (without heat). Another sample that started at 33% moisture and under 50 pounds increased by only 2 pounds after drying. Other samples from DeKalb and from Urbana all ended up at 56 to 57 pounds/bushel when dry. The only way to make sure you aren't docked for low test weight is to dry corn before taking it in.
Why do so many bushels "disappear" from wet grain I haul to the elevator? This season has been difficult for everyone, including elevators, which in some cases have had trouble delivering grain on time because grain is coming in so slowly. Drying capacity is also taxed to its limits this year, and in many cases dryers are simply not up to the task. This is no one's fault--we really can't spend what it would take to be ready for such an unusual year--but it does mean a lot of frustration added to what has been a frustrating year. Having 56,000 pounds of 28% moisture corn on a semi-trailer turn from 1,000 "wet bushels" into 818 dry bushels (13 points lost times 1.4% shrink per point lost) and paying more than 40 cents per bushel on top of that for drying takes a large chunk out of the value of the load. These losses are much larger than we have commonly seen simply because the grain is so wet.
One thing to remember is that the added weight due to extra water in wet corn was never really "grain yield" to begin with; it's only water that never got the chance to evaporate from the grain. So it's more accurate to consider only the "dry bushels" when we think about how much corn is on the truck--"wet bushels" are part water, so they aren't really grain bushels. It is true, however, that a shrink factor of 1.4 is larger than the "physical shrink" of about 1.2% per point. This protects the elevator against other weight losses, but in most cases it will mean that the buyer ends up with more bushels than were paid for. Again, the only way to prevent this is to dry grain before it's taken to the elevator.
How much loss can we expect as corn "weathers" in the field? If mold is continuing to grow on and in kernels, kernel weight will continue to decrease. If the grain is relatively bright with little damage, then kernels should be able to keep their weight almost unchanged. There have been a few reports of sprouting, most commonly when water has sat in the husks at the base of ears that have remained upright, but the cool temperatures have helped reduce sprouting. The biggest threat now for yield loss as corn sits in the field is dropped ears and serious lodging with stalk breakage, which can mean that ears detach and stay on the ground. You can shake stalks to see if ears stay attached; in most cases, if shank strength is good now it should remain good enough to hold ears to harvest. We do not think that any significant "dry matter loss" occurs as healthy grain dries, especially with the lower temperatures we are having now. If we do get unexpectedly good drying conditions before harvest, chances for kernel loss at the corn head increase quickly as kernel moisture drops into the lower 20s. Weakened cobs might contribute to such loss.
While it is difficult to predict harvest loss as a function of time that mature corn spends in the field, chances are good that field losses shouldn't increase too rapidly if the weather stays reasonably good into November. At the same time, it takes only about 2 kernels per square foot or one ear for every 250 square feet or so to make a bushel per acre.
Might it pay to leave corn in the field even after it reaches the mid-20s in moisture? Soybean harvest will take priority over corn harvest in many areas, so corn may reach 25% moisture or less before it can be harvested. If the crop seems to be standing well and keeping its ears, waiting until grain loses a few more points of moisture might in some cases pay, but this also increases risk. At a yield level of 200 bushels per acre, corn at $3.50 per bushel, and drying charges of 3.5 cents per bushel per point, shrink and drying "overage" totals a little more than 4 cents per point per bushel, or about $8 per acre for each point of moisture lost in the field rather than dried artificially. If the weather forecast is good, this savings might well exceed the potential field loss. Of course, corn is never really safe until it's in the bin and dried, so most people will opt to keep the combine running, even if this could cost more than additional field drying could save.Can we do tillage after late harvest? With a great deal of compaction last spring, many had hoped to take advantage of dry soils this fall to do some compaction-relieving deep tillage. With soils wet and unlikely to dry much before freezing weather, this hope might not be realized. It does little good to try to shatter soils to relieve compaction when the soil is wet; chisel or ripper points simply "mud through" wet soils and relieve few problems. This is likely to be the case next spring as well, which might mean that we "re-compact" soils during the planting operations next spring, and again have to hope for good rainfall next year to help minimize negative effects of compaction. So while deep tillage might not be helpful, shallow tillage, including shallow strip tillage, might provide a soil surface that warms and dries a little earlier next spring. Just remember that any trip over the field, other than one made when soils are frozen, can cause even more compaction.--Emerson Nafziger