Get dry-weather strategy for corn
Dry conditions crept into Iowa late last summer like an unwelcome stray pet. We recognize its downsides, but we also realize that some good can, and did, come of it.
Crop year 2011 is in the rearview mirror. As we look back at 2011, corn yields were compromised in many areas of the state in part due to dry conditions during late grain fill. Statewide yields suffered. Although the 2011 state average corn yield of 172 bushels per acre was 7 bushels above that of 2010, it still fell short of the 177 bushel-per-acre trend-line yield. But remember some of the positives relative to corn production, too: early harvest, dry grain, less soil compaction during harvest, excellent conditions for fall tillage and fertilizer application — and we could add a few others.
What does the current soil moisture situation indicate for the 2012 crop? As I write this, dry conditions persist. When we welcomed in the new year, nearly all of the topsoils in the northwest Iowa cropping district were either short or very short of soil moisture. More than half of the topsoils in the north-central, west-central, central and southwest Iowa cropping districts were either short or very short of soil moisture. Iowa State University climatologists say there is some probability that these dry conditions will persist.
What if it’s dry at planting in 2012? Two management ideas quickly come to mind:
• Reduce tillage as much as possible. Every tillage pass wastes a quarter-inch of topsoil moisture. In most years, we can afford to lose some, but in a dry year, every drop of soil moisture is precious. Conserve it by reducing tillage and keeping crop residue on the soil surface.
• Manage weeds well. Weeds soak up precious soil moisture.
Look at simulated yields
What are the probabilities of having reduced yields, with dry soil conditions at planting time?
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. In lieu of that, I used a corn simulation (computer) model with historic weather 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. I compared these two: 75% field capacity, or FC, topsoil and 100% FC subsoil versus 50% FC topsoil and 50% FC subsoil.
I realize that right now (late January) some soils are drier than 50% FC, especially in northwest Iowa, so the second possibility may be overly optimistic for those areas. Without changing hybrids or plant populations and with the drier soil at planting, probabilities of reduced yield vary depending on the location: NW R&D Farm, 75% of the time; NE R&D Farm, 50%; Central R&D Farm, 25%; SW R&D Farm, 75%; SE R&D Farm, 75%.
That suggests that if soils were dry at planting at the northwest, southwest and southeast R&D farms, yields would be reduced to some extent in three out of four years. Probabilities for lower yields are half or less for the northeast and central sites.
What about planting earlier-maturing corn hybrids? Any advantage?
Some corn-growing areas of the U.S. normally are not so blessed with good soils and precipitation at planting. Corn farmers in those areas sometimes use early-maturing hybrids to help mitigate drought conditions.
Given the two soil moisture situations at planting, we can simulate the effects of changing hybrid maturities for comparison. The model assumes a generic hybrid and models corn growth based on temperatures, solar radiation and precipitation actually recorded in the weather database for each R&D farm.
I used two hybrids at each location: a full-season and an early-season hybrid. The full-season hybrids at the northwest and northeast sites required 2,500 growing degree days (about 105 days relative maturity), while the early-season hybrid required 2,400 GDD (about 100 days RM). At the central, southwest and southeast locations, the full-season hybrids required 2,600 GDD (110 days) and the early-season hybrid required 2,500 GDD (105 days).
Interestingly, yield estimates for early- and full-season hybrids were consistent across both planting situations, whether soils were relatively moist or dry. The analysis shows clearly that hybrids of both maturities should be grown to spread risk and maximize yields.
Important to spread risk
The simulated data mirror actual yields obtained from the ISU Corn Hybrid tests. These tests are conducted annually at 20 or more locations each year with a full-season and an early-season hybrid trial at each site. Means (the mean average yield) of the two trials at any location are usually similar. Again, this suggests planting both early- and full-season hybrids is important to maximize yields while spreading risk.
We all know that many things can happen between now and planting. If soil moisture conditions do not improve, what I’ve tried to explain here is that planting diverse hybrids with a range of maturities is a good approach — as it is every year. Meanwhile, may that unwelcome stray pet find another home this year! 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 February, 2012 edition of WALLACES FARMER.