By ROGER ELMORE
Dry conditions persist in many parts of Iowa as I write this column. Last month I wrote about the impacts of dry soil conditions at planting on yield in different parts of the state using a corn simulation model (computer model).
In that analysis we learned if we plant into dry soils in 2012, based on long-term weather patterns, we’d have a 50% chance of yield reductions in northwest, southwest and southeast Iowa. For northeast Iowa, there’s a 25% probability of yield reductions if we plant into dry soils. In central Iowa, we would need to have a year like the worst one we’ve had since 1986 to experience yield reductions if soils are dry at planting; that carries a 4% probability.
Last month we also addressed the question whether shifting to earlier-season hybrids would improve yield potentials over full-season hybrids if we need to plant into dry soils. Yield estimates for early- and full-season hybrids were consistent, whether soils were relatively moist or dry at planting. That means that hybrids of both maturities should be grown to spread risk and maximize yields.
In Corn Belt areas with poor soils or reduced rainfall, farmers often reduce plant populations to compensate for conditions. Is that something we should consider in Iowa if conditions remain dry at planting?
What if it’s dry at planting?
What if it is dry at planting in 2012? Should you consider lower plant populations? As in February’s column, I used a corn simulation model (Hybrid-Maize) to answer this question. The simulations used historic weather data from automated weather stations at 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. I modeled two soil-moisture scenarios:
• 75% field capacity (FC) in the topsoil (0-12 inches) and 100% FC in the subsoil (12-40 inches)
• 50% FC in both topsoil and subsoil
The model assumes a generic hybrid and simulates corn growth based on temperature, solar radiation and precipitation actually recorded in the weather database for each R&D farm.
For these comparisons, I used a single hybrid at each location:
• Northwest and northeast locations — 2,500 growing degree days (about 105 days relative maturity)
• Central, southwest and southeast locations, 2,600 GDD (about 110 days RM)
The major change in these simulations from that discussed last month is I assumed final plant populations of 27,000, 32,000 and 37,000 plants per acre at each location with each of the two soil moisture scenarios at planting.
Yield estimates were consistent across both scenarios for soil moisture at planting for the three plant populations. Although estimated yields were often greater when planting occurred with moist soil vs. dry soils, the population effects were relatively consistent across both scenarios.
The modeled yields show that higher plant populations improve the chances for higher yields in high-yielding years. In lower-yielding years, yields resulting from different plant populations are similar; thus, seed costs associated with higher populations may not be offset by yield increases in lower-yielding years. But the probabilities of greater returns from higher seeding rates in better years would seem to counterbalance those concerns.
Summary: As mentioned in last month’s column, we all know that many things can happen between now and planting. If soil moisture conditions do not improve, that is if soils are dry at planting, what I’ve tried to explain here is that planting to achieve high plant populations is a good approach — as it is every year.
Plant populations between 34,500 and 37,000 per acre maximize yields in Iowa, while populations between 30,000 and 35,000 maximize net income. Meanwhile, let’s hope for complete recharge of our soil moisture before planting!
Elmore is the Iowa State University Extension corn agronomist.
This article published in the March, 2012 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2012.