The yields estimates that USDA completes aren't geared necessarily to accounting for large losses of nitrogen that may have occurred during the growing season. Eventually, it should show up in smaller ears and perhaps fewer kernels per ear. The first estimate released in August was based on data that did not even begin to assess ear size. Most of the fields checked for that report didn't have developed ears then. The report coming out in a few days based upon what field enumerators find now will be the first indication of ear size and kernel number per ear.
"Our work is showing that nitrogen loss is going to be an issue," says Justin Welch of Co-Alliance. He works in north-central Indiana as an agronomist and precision farming specialist. Welch has spearheaded a program involving flights of fields to take pictures and produce infra-red images to give producers more information about field performance. One of the things showing up in their early-to mid-August flights is that many fields are running out of nitrogen. Not surprisingly, it's worse where N was fall-applied. On many dark, level soils in his area fall application of N is still a fairly common practice.
In infra-red images, green, healthy vegetation shows up as dark green. Yellowish and reddish areas indicate that there is less growth, indication a problem. "The secret then is going into the field and finding out why it's that way," Welch explains. "You just can't look at an image and say it's nitrogen loss or some other factor. Ground truthing is an important part of the system."
In this case, many of those trips into the field to investigate areas that didn't show up as healthy on the flight maps have confirmed that indeed, lack of nitrogen is the issue. While fields were green in earlier flights during the season, now as ears fill, classic signs of nitrogen deficiency, including paler green leaves and stalks, and firing of the bottom leaves, are appearing, he notes. In N deficiency, the leaf fires down the midrib to the tip first. If the deficiency becomes severe, the firing may eventually turn into a tan, dead appearing leaf. If it's potassium deficiency instead, the firing will be around the outside edge of the leaf, not down the midrib.
Arlan Suderman of Farm Progress, a market specialist, published a graph earlier in Indiana Prairie Farmer showing what happened during the big '93 flood in the western Corn Belt. USDA corn yield estimates dropped significantly at each projection date from the initial estimate through final yield. Agronomists confirmed that season that running out of nitrogen due to excessive losses early in the season played a key role in reduced yields.
Driving through east-central Iowa to the Farm Progress Show a week ago, it's not difficult to imagine that scenario repeating. Since Iowa rolls, it's possible to see nearly whole fields on an angle from passing by, and get a look at the corn over the top. In nearly every field it wasn't difficult to pick out lighter green areas, and not just small spots, especially on the sides of the hills.
Better hybrids that produce in tougher conditions and perhaps use N more efficiently than those of 15 years ago may play a role in mitigating this effect. But many people believe it may be a real factor that plays into dropping the trend yields that USDA arrives at before final yield is posted for the '08 crop later this year.