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Issue No. 22, Article 6/September 7, 2007

Notes Heading Into Harvest 2007

A few notes as we head into harvest of the 2007 corn and soybean crops:

  • Most of the corn fields planted in April are at physiological maturity (black layer) in central and southern Illinois and rapidly approaching maturity in northern Illinois. Early reports from southern Illinois, where unusually large percentages of the crop are already harvested, are of yields ranging from poor to better than expected, all depending on how much rain fell during the growing season, especially during July and August. In most fields, the growing degree day requirements of the hybrid used were met, or nearly met, even though the crop appeared to dry up prematurely in some fields. This should mean that yields might be higher than the dry, hot weather of August had us thinking they would be. Every indication is that pollination was good in most of Illinois and that grain filling took place at a fast rate.
  • The damage suspected to have resulted from fungicide application to corn is "clear and present" in some fields, but reports of such damage have not been flooding in since I reported on this in early August. I have come to believe that the rapid growth of the crop following the dry weather that was relieved by rainfall around June 20 might have been an important factor in predisposing the crop to injury. Nearly all reports of injury we have received involve corn that was planted a little late (early May) and sprayed well before tassel emergence. Differences among hybrids in their susceptibility to this damage seem to be more related to the exact growth stage at the time of application than to differences in genetic tolerance. Those who are still looking at fields, or who believe they have injury from fungicide application, should remember that not all cases of undersized ears result from damage due to fungicide. Variable ear size and ears that have "nosed back" (with unfilled kernels on ear tips) are found in virtually every corn field in Illinois. In fact, the only way that comes close to proving damage from fungicide (or any other cause) is having an untreated check that is representative of the rest of the field (that is, is placed in an "average" strip) and that shows consistently higher yields than the treated areas on each side of the check. Without such a check strip, there can be no accurate estimate of how much yield loss occurred. The distinctive feature of the fungicide injury I have described is that the ends of the ears, or whole ears in extreme cases, consist of shrunken "baby corn" tissue, with no silks visible, that appears to have stopped developing suddenly. The ear below such damage may look normal, with normal-sized kernels.
  • Some people are making a great deal of the fact that grain fill ended during dry weather, which tended to deplete the stalks of sugars and to result in weak stalks. Indeed, stalks are weak in many fields, especially where kernels filled out well and leaves dried up early. High winds associated with storms have affected relatively little of Illinois, however, and so stalks are still standing in most fields. In the parts of western Illinois affected by high winds during the last week of August, stalks fell or broke over no matter how strong they were. The point is that many producers are taking an acceptable risk by allowing corn to dry down in the field, even in fields where stalks are weak. Drier grain at harvest means both lower drying cost and better ability to harvest fast when grain does not have to be dried with heated air. Combines are improved as well, and harvest losses for grain at 20% moisture, or in fields with lodged corn, are less than they were at one time. For these reasons, many consider 20% to be reasonable harvest moisture. With the warm weather we have had following maturity, corn grain has lost moisture rapidly, perhaps approaching a full percentage point on a hot day with low humidity and a breeze.
  • With current concerns about the effects of weather on test weight, this is a good time to review test weight and what it means. Test weight is affected by kernel density, size, and shape as well as by moisture and condition of the seed coat. Hybrids differ in test weights, and any of these factors might affect such differences. I have looked at the relationship between test weight and yield in corn hybrid trials and have never found a strong correlation. So why are people worried about test weight? Within the same hybrid, lower or higher test weight is often related to kernel weight, which is often correlated with yield. A kernel that does not fill very well with starch has lower endosperm density, so lower kernel density, meaning that it has less weight for its volume. This often registers as a drop in test weight. So an early end to grain fill often does mean lower test weight, though this may not be exactly proportional to lower yield. Test weight is used as a proxy for things like kernel density that are hard to measure directly. We can have average test and high yields in certain hybrids, but there has been some movement by seed companies away from hybrids with low test weights. Some of this is aesthetic--kernels with high test weights often look bright and attractive and feel "weighty"--but it also has a practical benefit in that more "bushels" (56-lb units) fit into a bin when test weight is high than when it is low.
  • With corn following corn expected to increase again in 2008, there will be a lot of emphasis this fall on managing corn residue in order to make planting corn next spring less troublesome. Fine-tuning tillage operations is probably the most direct way to do this, burying some of the residue to get it out of the way and leaving some on the surface to reduce erosion. Some people apply nitrogen in the fall to try to stimulate organisms to break down residue faster. While this seems logical based on the low N content of residue and the fact that organisms need additional N to complete the breakdown of residue, attempts by researchers to show a yield advantage to fall application of N have never been successful. Claims that some dry forms of N work better for this than liquid forms are puzzling, since dry forms would not place much N in contact with residue, at least not quickly. Some of the N in UAN solutions will be lost quickly due to urease in residue if tillage is not done soon after application. But the primary problem with the logic of providing N to hasten the breakdown of corn stalks is that microbial breakdown of stalks is much more often limited by soil moisture, temperature, and the contact of residues with the microbes in soil than it is by N availability. Beyond the physical weakening of stalks so they break more easily at spring planting, benefits from early stalk breakdown are unclear. One thing is clear: If the N added to stalks in the fall is considered a "stalk breakdown aid" and not as part of the N fertilizer applied to next year's corn crop, then such fields are simply being supplied with more N. Higher yield from the additional N could be the real effect of such applications, rather than any effect on stalk breakdown. Is the added expense necessary, and does it return its cost?
  • Plants are starting to turn yellow in soybean fields planted with early varieties, though harvest of soybean is starting a little later than that of corn. Though it appears that soybean yields will not be unusually high in most areas, the crop after leaves have dropped seems to have at least average pod numbers, even where it appears to have reached maturity sooner than normal. I have learned not to make yield estimates until the combines roll.
  • One concern has been the effects of sudden death syndrome (SDS), and perhaps too-wet soils in some places, on how well the seeds will dry down to allow combining. Some fields have areas where the plants are still green and other areas with few leaves still attached to plants that in some cases still have green stems and pods. The supply of sugars to the pods and from pods into the seeds slows greatly when leaves are lost. But any tissue that remains green on such plants, including pods and stems, remains capable of at least some photosynthesis, so filling might continue at slow rates. The real problem might develop when stems and even pods stay green after normal plants have lost all green color and are ready to combine. Seeds in such pods are high in moisture when the leaves drop, and so need to lose a lot of moisture, but moisture loss through green pods is slow. If this "green problem" occurs in patches in the field, some might want to cut around these patches and leave them to combine later. This could also help to isolate green seed that might result from premature leaf loss and could be subject to dockage at the elevator. There is not much that can be done to make green stems or pods dry down faster. Gramoxone might help to dry up pods (but not stems), but it could reduce yields some if green pods are helping to fill seeds, and it might be too early to apply it to the healthy parts of fields. Depending on the weather, green pods might dry down at about the same time as healthy plants, and harvest problems might be avoided.

--Emerson Nafziger

Author:
Emerson Nafziger

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