No. 15 Article 6/July 1, 2005

Still Waiting for Rain

The most recent corn crop condition report shows an Illinois corn crop in serious decline, with 40% of the crop rated as "fair" and the rest about equally split between "poor" and "good." These are some of the lowest current crop ratings among states and are among the lowest we have had in recent decades, especially this early in the season. It is difficult to look at a field with leaves tightly rolled before noon and see much potential, but we still hold out hope that the ratings are pessimistic and that rain will fall in time to restore the crop to at least modest productivity. Somber statements to the effect that "It doesn't matter much now if it rains or not" are surely premature. On the other hand, we have to acknowledge that the situation is serious, and yield loss is accelerating as we continue without rain. As is so often the case, the only thing that can bring yield potential back to anything close to "trend" levels is for the weather to turn unusually favorable, with above-average rainfall in July and consistently moderate temperatures, with a long "end" on the season, such as we had in 2004. Chances of that happening are not high.

One of the indicators of unusual stress this year is the lack of plant growth. As I wrote before, plants are usually able to take in enough water at night to expand their cells and grow in physical size, even after soils get dry enough to cause leaf curling during the afternoon. Leaf curling for much of the day means little photosynthesis, and lack of cell expansion and growth at night is a result of both lack of photosynthesis and lack of even the ounce or so of water needed each day for physical growth. Soils dry enough to inhibit plant growth thus have almost no plant-available water to the depth that roots are active, and the best we can hope for is for such plants to just stay alive. In a few spots in fields that were planted late or in light or compacted soils, plants have started to show the sickly gray color that comes before the death of leaves. That's not widespread, but we cannot expect plants to last long once they start to desiccate, any more than we could expect other living things to do that.

Much of the early-planted crop in Illinois has accumulated enough growing degree-days since planting that we would be expecting tassels to appear within the next week or 10 days. In places where conditions are dry enough to reduce or stop growth, however, the GDD system of predicting growth and development has broken down. The corn crop in many fields in the driest part of the state has grown only a foot or so through the middle 2 weeks of June, even though GDD accumulations during this period were average to above average, and so enough to cause the appearance of five or six leaves and 24 inches or so in height. The official statistics also confirm that the average height of the crop has fallen to normal, after being above normal at the end of May. Height and crop progress are well behind what they were after the warm, wet weather in May in 2004.

The fact that plants are coming through a period of high temperatures without growing as much as they should is a phenomenon that we have rarely seen in Illinois, and hardly at all since 1988. This phenomenon has hardly been recorded in the literature. We might think of plants like this as being in a "suspended" state, often able to stay alive but with so little water available that they do virtually no photosynthesis or growth. In 1988, I observed that such plants often retained the ability to grow and develop after rain fell, but their growth was not always well synchronized, even though some did produce 50 to 70 bushels per acre where we had expected them to produce nothing at all.

What can we expect if it does rain soon on crops that have undergone stress for this length of time? In most fields, the response will be dramatic, as cells start to take on water and photosynthesis starts back up. Roots should get a charge of plant nutrients that they need. But we do not expect such plants to grow to their normal size, and this will likely mean some degree of yield loss. If rainfall resumes its normal pattern of starts and stops, some plants may grow enough to produce tassels but may run out of water before silks appear, leading to problems with the pollination process. Silk elongation is one of the most water-sensitive growth processes in the plant. On the other hand, plants with compromised canopy cover from restrictions on leaf size may not be capable of filling a lot of kernels anyway, so lowered kernel numbers may not limit yields in such fields.

It's no fun painting such a picture of the corn crop in Illinois, and I really hope that rainfall over the next week brightens this picture somewhat. We will get rain again, but our run of 10 years during which corn yields continued to increase steadily in much of Illinois may end in 2005. Soils, hybrids, and management have resulted in a real increase in resilience of this crop, and we can at least take some comfort in the fact that, if we had gotten these Dust Bowl weather conditions without such improvements, we would be writing much of the crop off by now. So we can still hope for good yields--and the market seems to think we have reason to--but at the same time we need to realistically expect lower yields in most fields than we got last year. Exceptions will be where the spotty rain showers happen to land and where stress on the crop has been minimal.

There has been considerable talk about how many inches of rainfall "deficit" have accumulated, with some implication that we can't expect a good crop unless we make up this deficit. This is somewhat misleading, in that the crop will respond to the moisture that's available and getting 6 or 7 inches of rainfall needed to overcome the deficit of the past 3 months is both unlikely and perhaps even detrimental, especially if it happens quickly. While rainy weather in July would be a plus, we need a lot of sunshine along with enough water to meet daily demands. Thus a return to normal rainfall, if it is well distributed, would likely provide enough water to finish out the crop and would probably be a better situation than getting twice the normal amounts for the next 2 months. We can certainly produce a good crop with less water than it takes to bring accumulated annual rainfall up to average levels.

Much of what I have just discussed about corn applies to soybean, especially the restriction of growth that we're seeing in the driest areas. Flowering is getting under way in many fields, as we expected with the warm temperatures, though as I indicated before, we do not expect many of the early flowers to develop into pods as long as it stays dry. The concern that soybean won't fill its canopy very well in wide rows will continue to increase as long as it stays dry. Plants will continue to increase in height and leaf area only until early August or so, and the longer they stay short now the shorter they will likely end up.

The winter wheat story is a fairly positive one this year. Harvest is about 75% complete in the state, and we harvested the Urbana variety trial on June 28, with only the DeKalb trial yet to harvest. Yields will not break records, but quality is good and prices are reasonable. Struggling full-season corn and soybean crops also make wheat look like a good option in some areas. On the negative side, many fields eligible for double cropping have been too dry for good soybean establishment. Rainfall in the next week will help but will also mean a slow start, which for double-cropped soybeans usually means lowered yield potential.--Emerson Nafziger

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