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Issue No. 15, Article 6/July 3, 2008

Crop Condition: The Real Test Lies Ahead

Recent reports show gradual improvements in the condition of the Illinois corn crop, from 48% good to excellent on June 8 to 60% on June 29. I traveled north as far as DeKalb and south as far as Farina this week, and there is no question that the periods of dry, sunny weather over much of Illinois in recent weeks have helped the crop get back to some semblance of normal. Growing degree day accumulations from May 1 through the end of June average only 70 less than average, reflecting a cooler-than-normal May followed by a warmer-than-normal June. June provided a good mix of warm and cooler temperatures, with no extremes, which has been very helpful to recovery.

One exception to the return to normal is late-planted fields. Some cornfields in central Illinois were planted (or replanted) in June, and plants are now only about a foot tall. Many fields in south-central and southeastern Illinois were replanted or "repair-planted," and it will be interesting to watch how the early-planted plants left standing will compete against the later-planted plants. In general, we expect the early-planted plants to compete well for water and nutrients, and to lower yield of nearby late-planted plants more than they increase their own yield. This will lower overall yield, especially in those parts of repaired fields with a lot of early plants, where the total plant population is much higher than normal. The late-planted fields have improved in color and growth is starting to accelerate, but these fields will not catch up quickly, and the high temperatures it would take for them to catch up at all would likely do more harm than good.

While a considerable amount of unevenness is present in many fields where water stood earlier, crop color is much better in most fields than it was a month ago. In much of the northern half of the state, the corn crop is in very good shape, with good stands and the deep green color that reflects the fact that roots are tapping into nitrogen well. There are some drowned-out low areas, and what appears to be loss of N, along with some easy-to-see errors in N application. But the rainfall in most areas in mid-June has helped move N to roots, and concerns about lack of N, along with the urge to take corrective action, have decreased.

Much of this improvement has come about because soils have dried out and warmed up, considerably improving the ability of the roots to do their job. Still, soil conditions were generally not very good at the time of planting, and it is not likely that even the most favorable weather will overcome that handicap. Most of this will play out as a limitation on the root system to take up water during dry periods. Even now, we are starting to see some leaf curling in the afternoon, indicating that the crop is unable to take up water as fast as the plant is losing water to the air. By itself, this mild stress is not a big concern before tasseling. But it does indicate that roots are not as extensively connected to soil water as we would like them to be, or as they were at this point in 2007. With June rainfall well above average over most of the state this year, and with the largest crop's having used only 5 to 6 inches of water by now, there is certainly water available in the soil, even though much of it may lie below the zone of active rooting. The best possible situation is to have little or no occurrence of dry soils in the rooting zone over the two months.

Crop use exceeds average rainfall totals by 3 to 4 inches during July, so avoiding periods of dry soil will require that rainfall be above normal. Most importantly, we would like to have plants well supplied with water for two weeks before pollination, through pollination, and for two weeks after pollination. For the Illinois corn crop this year, this means that July has to be a good month, with above-average rainfall, to fully meet the needs of the corn crop. Positive signs now are the much-improved canopy condition, which will help the crop take full advantage of the sunlight and water it gets. But the old saying "Rain makes grain" has never been truer than it will be this year.

The soybean crop continues to struggle, with the crop in many fields still only a few inches tall, and canopies ranging from reasonably good in those fields planted earlier (this year, "earlier" means during the second half of May) that escaped excessive rainfall. Like the corn crop has done, we expect the soybean crop to "jump-start" its growth soon in late-planted fields. At the same time, the crop has by now lost the use of practically a whole month of sunlight, and it will be difficult for the crop to manage even modestly complete canopy cover as it heads into flowering and then into pod-setting. That puts pod numbers at risk, and without adequate pod numbers, yields will suffer. While a good water supply during July will help the crop extend its flowering period and so will increase pod numbers, the soybean crop will recover its yield potential only if the good moisture supply extends through August and into September.

Wheat is one positive that we can put into the books for the 2008 cropping season in Illinois. Harvest is late, and is just now reaching up past I-70; combines were running on July 1 in the Vandalia area. Our concerns about late heading were mitigated by the good conditions during June, and the late harvest reflects the fact that the crop needed its usual 6 weeks from heading to full maturity to produce good yields. Double-cropping is clearly the order of the day, with many of the double-cropped soybeans planted little later than the "full-season" soybeans in many areas. We expect double-cropping to extend farther north than usual this year. The fact that normal soybeans were planted late means that double-cropping is less risky, but only in comparison to normal soybeans, not in an absolute sense. We would suggest that soybean planted following wheat harvest north of Route 16 or so be slightly earlier in maturity than full-season beans, but those at the earlier end of the range of normally planted soybean varieties should work. Do not plant this late in rows wider than 15 inches. With tall plants and heavy straw, double-cropping will probably work better if straw, at least the straw run through the combine, can be baled off before soybean planting. If that is not done, then cut as high as possible to reduce the amount of straw chopped back onto the ground.

Early wheat yield reports, and the appearance of the crop before harvest, are outstanding. One unusual feature is the bright yellow color of the harvested straw--it looks almost like oat straw. We expect to hear about yields in the 70s and 80s, and even 90s, though excessive water in parts of southern Illinois will have damaged some fields and lowered yields. But if corn and soybean crops make a comeback like the wheat crop did, we might still remember 2008 as a good year.--Emerson Nafziger

Author:
Emerson Nafziger

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