Grim News for Illinois Crops

The latest USDA Illinois Weather and Crops report was released this afternoon. The topsoil conditions were rated at 52 percent “very short” and 37 percent “short” and only 11 percent adequate. Soil moisture conditions were best in northern Illinois, and deteriorated southward. Hardest hit was southeastern Illinois with 100 percent of the topsoil and 100 percent of subsoil rated as “very short”.
The corn crop was rated at 12 percent “very poor” and 21 percent “poor”. The soybean crop was rated at 11 percent “very poor” and 20 percent “poor”.
Several people have compared this year to 1988. How bad was soil moisture in 1988? According to the USDA report for July 5, 1988, the entire state was listed as 100 percent “very short” on topsoil moisture. However, they rated the corn crop at 2 percent “very poor” and 20 percent “poor”. The soybean crop was rated as 2 percent “very poor” and 14 percent “poor”. So they rated the soil moisture to be in worse shape yet they rated the crop to be in better shape in 1988, compared to 2012. It’s hard to make sense of the numbers. Of course, these are subjective ratings and the procedure for rating crops and soils has likely changed with time.

Soil Moisture in Illinois

Observed soil moisture data are collected at 19 sites in Illinois by the Illinois State Water Survey’s Water and Atmospheric Monitoring program. The soil moisture is measured at 5 cm (2 inches), 10 cm (4 inches), 20 cm (8 inches), and 50 cm (20 inches). All amounts are reported as the fraction of water by volume of the soil. For example, a value of 0.35 means that 35% of the soil is occupied by water.
Silty clay loam soils, common in Illinois, are considered saturated at values of 0.45 to 0.50. Field capacity is in the neighborhood of 0.35. Values below about 0.20 would be at the permanent wilting point. As the name implies, that is the level where plants wilt and do not recover. Plant roots are unable to recover any water below this level because it is tightly bound to the soil particles. Of course, soil moisture is very dynamic with layers drying or wetting at different rates so it would take low levels of soil moisture at all layers in the root zone to kill a plant.
In general, soil moisture is highest in spring and slowly declines in the summer months because of the heavy demands from evaporation and from transpiration of growing vegetation. In the fall, cooler temperatures and the end of the growing season allow soils to recover quickly.
The map below shows the May 14, 2012, soil moisture status at 10 cm (4 inches). Values in the 0.2 and 0.3 range are widespread. The noticeable exception is in Mason County where the site is located on a very sandy soil. As a result, the moisture drains right out of the soil after a rainstorm.
Linkhttp://www.isws.illinois.edu/warm/soiltemp.asp
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Latest Soil Moisture and Drought Monitor for Illinois

Observed Soil Moisture

The Illinois State Water Survey has been monitoring the soil moisture at 19 sites around the state. The soil moisture is measured with probes set at specific depths at each site. It is reported as the fraction of water in the soil by volume. Most of the non-sandy soils in Illinois can hold up to 30-40 percent water by volume in the spaces between the soil particles.
Current observations in the driest areas of the state show significant declines at 2, 4, and 8 inches since early March. At the Peoria site, in the heart of the dry area, the fraction of water in the soil is only 15 percent at 2 inches, 18 percent at 4 inches, and 22 percent at 8 inches. The 20-inch depth has remained unchanged at 32 percent. By comparison at the end of April of last year, the fraction of water in the soil at those depths were all in the 35-40 percent range.
We are in the process of getting these data online in the next few weeks. Stay tuned.

U.S. Drought Monitor

The latest U.S. Drought Monitor map for Illinois shows an expanded area of D0 “abnormally dry” weather across the central part of the state between Interstates 70 and 80. A small area of D1 “moderate drought” is located in the area centered on Logan County. Another small area of D0 is in southeastern Illinois.

Here is what the U.S. Drought Monitor says for Illinois. Click to enlarge. Link to original (updated weekly). Released on April 26, 2012.

Return of the Soil Moisture in Illinois

The natural rhythm of soil moisture in Illinois is to be abundant in spring (sometimes to the point of water standing in fields), followed by a prolonged draw-down during the growing season. Historically, soils are usually at their driest at the end of August and early September. However, soil moisture begins to recover in the September/October time frame as the temperatures cool and crops are harvested, even if rains are below average.
We are seeing some recovery in soil moisture now, according to our soil moisture network maintained at the Illinois State Water Survey. Here is the average soil moisture in the top 20 inches, expressed as a percent of what we saw on June 1 when soil moisture was very high. In other words, values near 100% show a near full recovery while values less than 100% need more rain to recover.

  • Belleville: 88%
  • Big Bend: 93%
  • Bondville: 57%
  • Brownstown: 68%
  • Champaign: 75%
  • Carbondale: 52%
  • DeKalb: 75%
  • Dixon Springs: 106%
  • Fairfield: 89%
  • Freeport: 86%
  • Monmouth: 55%
  • Olney: 78%
  • Peoria: 87%
  • Perry: 47%
  • Springfield: 67%
  • Stelle: 71%
  • St. Charles: 58%
  • Rend Lake: 71%