Iowa 2012 corn yields ended at 137 bu/acre (see USDA-NASS data), dropping 22 percent below the 30-year trend line yield of 180 bu/acre. For comparison, in 1988 Iowa corn yields were 29 percent below trend line. Based on the U.S. Drought Monitor and modeled soil moisture data from Mesonet (Volumetric Soil Water Map), 2013 conditions so far appear worse than those of 2012. Optimism wanes for normal soil moisture profiles at planting. That concerns most of us connected to agriculture across Iowa, which really should be everyone! Remember, soil moisture conditions were a hot topic for us last winter as well. I addressed that situation beginning with a series of ICM articles in January 2012 (Part 1, Part 2, Part 3).
It doesn’t surprise any of us that in areas of the Corn Belt with poorer soils and/or reduced rainfall, farmers typically reduce plant populations to compensate for conditions. Is that something we should again consider in Iowa if conditions remain dry at planting? In part based on concerns at planting in 2012, Iowa farmers as well as those across most of the Corn Belt reduced plant populations relative to those used in 2011 for the first time since 2000. Iowa corn plant populations in 2012 dropped to 30,100 plants per acre (ppa) from 30,750 in 2011 (see Figure 8 linked in the endnotes). Albeit, that is not a huge decrease; but it does reflect pessimistic sentiments at planting in 2012. This change will slow the consistent trend of increased plants per acre of about 400 plants per acre per year since the turn of the 21st century. With that as history, what should we think about this spring?
Should you consider lower plant populations if it is dry at planting in 2013?
As in last year’s versions of these articles, I used a corn simulation model (Hybrid-Maize) to answer this question. The model uses historic weather data from automated weather stations. In this case, I used data from seven of Iowa State University's research and demonstration farms, one in each of the four corners of Iowa and the others in northern and west central Iowa and one near Ames in central Iowa.
- ‘Normal:’ 75 percent Field Capacity (FC) in the topsoil (0-12 inches) and 100 percent FC in the subsoil (12-40 inches), and
- ‘Very Dry:’ 25 percent FC in both topsoil and subsoil.