Part I: Yield prediction with dry conditions at planting
By Roger Elmore, Department of Agronomy
Dry conditions persist in many parts of Iowa. As of Jan. 30, modeled volumetric root-zone soil water in the northwestern half of the state was one-third or less (see Mesonet map). Elwynn Taylor, Iowa State University Extension and Outreach climatologist, indicates there is some probability that these dry conditions will persist.
What if it is dry at planting in 2012?
We don't have specific research experiments planted every year in Iowa to provide actual yield data for dry planting conditions — we don't often have dry soils at planting. However, modeling tools that simulate dry conditions at planting help us understand the effect of dry conditions on potential yield. The corn simulation model Hybrid-Maize can address several questions regarding corn management practices. The model uses historic weather data from automated weather stations. I used data from five of ISU's Research and Demonstration Farms, one in each of the four corners of Iowa and the other near Ames in central Iowa.
The model allows users to change soil moisture conditions at planting to simulate different possibilities. With this capability, we can address the question, "What if the soils are only half field capacity (FC) at planting?"
In this exercise I compared two moisture levels: A. 75 percent field capacity (FC) in the topsoil (0-12 inches) and 100 percent FC in the subsoil (12-40 inches), and B. 50 percent FC in both topsoil and subsoil. I realize that many soils now are drier than 50 percent FC so the second possibility may be overly optimistic for those areas. Other common inputs for each site modeled are provided in Table 1. Factors that varied across locations such as soil textures are shown in Table 2.
Without changing hybrids or plant populations, with drier soils at planting, probabilities of reduced yield vary depending on the location in the state (Table 3). If we have a year with weather conditions like those of 2011 at the five locations with the stipulation of planting into dry soils, yield potentials at the Northwest (NW) Sutherland, Northeast (NE) Nashua, and Central Ames research farms would be similar to what they would be if the soils were moist at planting. The weather experienced at each of these sites was sufficient to overcome any disadvantage of the dry soil planting conditions. However, at the Southwest (SW) Lewis farm yields would be 64 percent of those of a wet soil at planting; at the Southeast (SE) Crawfordsville farm, 70 percent.
Another way to think about yield potentials is to look at probabilities of experiencing a year that would provide yield reductions with dry soils at planting. A median year at NW, SW and SE would result in sizeable yield reductions if soils were dry at planting. A 25 percentile year would reduce yields at NE if soils were dry at planting, and only the worst year since 1986 would reduce yields at the Central location.
We all know that many things can happen between now and planting. If soil moisture conditions do not improve by planting, yields will be reduced at many Iowa locations. Meanwhile, let's hope for complete recharge of our soil before planting and a good year!
Endnote: This article and the two associated with it summarize portions of the 2012 Crop Advantage Series (CAS) talk entitled "Long silks, short pollen,... long year" presented in January 2012. Slides from that presentation with more detail are available here: CAS Presentation Slides.
Table 1. Hybrid-Maize model input factors that were the same across locations and years
Table 2. Hybrid-Maize model input factors that varied by location
Table 3. Effect of dry soils relative to wet soils at planting on simulated corn yield potential.†
Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at firstname.lastname@example.org or (515) 294-6655.