Thoughts At Harvest

DR. EMERSON NAFZIGER

URBANA, ILL.
    Corn and soybean harvest in Illinois stood at 5 and 1 percent, respectively, on September 22, 2013. These are behind the 5-year averages, and far behind the 51 percent of the corn crop harvested by this date in 2012. Using 5-year averages may be reasonable, but corn harvest progress by October 1 ranged from 4 percent to 71 percent over the past five years, so “average” does not describe “typical” very well.
    Harvest of both corn and soybean have ramped up in Illinois the last week of September, with corn leading the way but soybean harvest starting to pick up. Following are some observations as we start to get into fields to harvest both crops:
    Corn yields: As anticipated, yields of early-harvested corn have ranged from good to excellent, with many reported to be 200 bushels per acre or higher. This is truly remarkable in areas (such as here in Champaign-Urbana) where total rainfall for August and September has still not reached 1 inch. It’s certainly possible that yields would be even higher if we had gotten normal rainfall in August, especially on lighter soils. It’s also possible that any effect of dry soils might be larger – that is, yields lower – in corn following corn compared to corn following soybean. As I’ve noted before, ability to pull water from the soil seems often to be a little less in corn that follows corn, for reasons we don’t very well understand. It’s also likely that in areas where some corn got planted in late May or into June, stress effects will be more severe. So there will be considerable yield variability among fields, and late-planted corn could have considerably lower yields, especially if it died early from stress.
    Stalk quality: Stalk strength is good in most fields, and there have been few reports of stalk lodging. It’s possible, though, that some of the late-planted corn could have a problem in areas where stress started earlier in life cycle of the crop. What we have seen more commonly this year are “snapped” stalks, broken off at a node. Some of this was from wind events in the first half of the season; the typical greensnap period tapers off at about silking time as plant nodes strengthen, and involves breakage at nodes ranging from the ground level to about the ear node. But we are also seeing some fields where breakage occurred weeks after pollination, including some that appears to have happened past the middle of grainfill. This is an unusual phenomenon, and probably resulted from having strong internodes that don’t bend very much, so the stalks broke at the nodes instead. This might not decrease yield too much if it happened late in grainfill and if the stalk snapped above the ear. But in some fields stalks snapped below the ear, and the ears are on the ground attached to the upper stalk. These may be nearly impossible to pick up with the corn head. In some fields I’ve seen, this is a problem mostly on end rows that run north-south, but there are other fields where it’s more general.
    Roots: Most fields are standing well with good roots anchoring the plant, and they’ve obviously been able to take up water from drying soils in order to get grain filled. One issue that Dr. Mike Gray has written about is that of rootworm damage resulting in considerable root lodging in some fields in some areas. Such damage has been found under heavy CRW pressure in hybrids with different CRW Bt events and sets of events, including in SmartStax fields. Insect resistance has been confirmed only to the protein Cry3Bb1, a protein produced by a CRW Bt event that is widely used, including in SmartStax hybrids. But SmartStax hybrids also include the event that produces the Cry34/35 Ab1 protein, and CRW resistance to this protein has not been found. As is the case with weeds, insects, or diseases, the presence of the pest or of damage is never proof that the pest has developed resistance to the control methods used; such proof requires careful lab tests that confirm a change in pest genetics resulting in resistance. There have also been some observations of roots that simply appear to be smaller than normal, in some cases in corn that follows corn. By maturity, root systems usually have deteriorated to a considerable extent, and it’s never safe to assume that we can know the cause this late in the season, especially when possible causes (such as insects or diseases) are not present.
    Kernels: One indication that the crop retained enough green leaf area to fill kernels to close to their maximum size is having kernels that are deeper (longer from the point to the crown) than normal. Kernel depth is under genetic control to some extent, but high-yielding conditions often produce heavier kernels, and about the only way kernels on well-pollinated ears can increase in weight is by getting longer; their expansion is limited on all sides by other kernels. They can increase some in density of starch, but this is often high already, and there might be little ability to add weight without adding volume. In response to a question about how much an increase in kernel depth increases yield, I did the following calculation: Assuming that kernel density and how kernels “pack” on the ear stay the same, increasing kernel depth by 10 percent, from 0.4” to 0.44”, on a cob that’s 0.8” in diameter would mean a 21 percent increase in weight of kernels. Actual yield increases from deeper kernels could be less than this, but it illustrates the value of having a crop fill kernels right up to maturity. Another issue related to kernel development that has been reported this year is failure of the kernel to form a “black layer” even when grain moisture drops below 30 percent. This is related to the “extended” filling period, in that sugars may remain in the cob even after kernel fill would normally have stopped, so the layer of sugar-conducting cells at the tip of the kernel does not die and turn dark as it normally would. At the same time, starch in the endosperm is drying down, and such kernels have reached or are very close to reaching their maximum weight; even if some sugar is still present in the cob and tip of the kernel, there are no more cells with starch granules still forming, so the sugar has no place to go. Kernel tips with sugar like this will darken with artificial drying if not before, and I know of no negative consequence of failure to form a black layer at the exact time that kernel fill stops.
    Test weight: Many people consider the main benefit of deeper, heavier kernels to be their contribution to higher test weight. While we have no reason to believe that test weights are not within normal ranges for corn that matured normally, it is not always the case that deeper, heavier kernels will mean higher test weight. In some cases, larger kernels may not fit together as well as smaller ones, and could produce lower test weights, even as they produce higher yields. High yields, though, almost always have test weights within the normal range, typically between 54 and 58 lb per bushel. Under such conditions, while test weight does determine how many bushels will fit into a bin, it is of little importance as long as the grain meets the minimum. The minimum is not fixed because elevators can blend corn to meet export requirements, but it’s rare for high-yielding corn to get docked in price due to low test weight. We did see some of this in 2009, but that was following a very late end to filling and low starch density.
Aflatoxin: We’ve continued to get questions about the potential for aflatoxin following the dry weather of the last two months. We have heard no reports of aflatoxin problems so far in 2013. As a reminder, the organism that infects kernels and produces the toxin infects in mid-season, and infection is much greater when the conditions are hot and dry at that time. It was hot and dry in July in 2012, but not in 2013. It is possible that the earlier-harvested corn from earlier-planted fields might have escaped infection a little better than late-planted corn. But it was never very hot through mid-August, and it wasn’t very dry until after that. So our hope is that, as is the case most years, aflatoxin will not be an issue this year. One hint: if elevators are not testing, it’s probably a non-issue.
    Drydown: There have been many observations that even after this extended dry period and good drying weather, corn seems to be drying down slowly. This is connected to the fact that sugars have remained available to fully fill kernels out, and that yields are good. Under dry conditions, we often expect the crop to mature earlier than normal (and with lower yields) due to stress. That’s not happening. Instead, the crop is using its full complement of growing degree days. Corn planted on May 15 at   Champaign reached 2,700 GDD (the amount needed to reach maturity for typical hybrids used here) only on September 17, and corn planted on May 30 will not reach that total until the first week of October. With deep kernels that might dry a little more slowly, and in some cases with sugar at the base of the kernel that tends to hold moisture, it is not unexpected that grain moisture is at current levels. While it can be worrisome to wait for grain to dry down and to have drying costs on top of lower prices this year, good yields and a crop that is standing well are pluses in many fields. It’s also a good time to remember that very dry grain in the field usually means much higher shelling loss, and corn harvested at 20% moisture without much shelling loss and dried may often net more than corn harvested at 15% moisture. As we move into October, we can expect drying rates to slow, so corn that is not yet below 30 percent moisture will probably not get to 20 percent very fast.
    Soybeans: Early indications are that yields are fair to good, but there is some thought that the early-maturing soybeans (planted early or early maturity varieties) might have escaped some of the drought stress, and that later-maturing fields might not yield as well. A key indicator will be seed size; with pod numbers mostly better than last year and without the rain to prolong seedfilling this year, we expect to see smaller seeds in fields where stress ended the filling period. One benefit of having seedfilling end because of leaf loss is that greenstem, which is brought on when plants have more capacity to produce sugars than ability to move them into seeds, should not be much of an issue this year. As we expected might happen, many fields, once leaves drop, are not showing the number of pods that we would like to see. But seedfilling appears to have been at a good rate before leaf drop in areas that had a little more rainfall or where the crop was planted early, it’s possible that yields will be a little better than we might have expected a month ago.∆
DR. EMERSON NAFZIGER: Professor, Research Education Center Coordinator, University of Illinois