Looking Ahead--Corn And Dry Soils At Planting In 2012

Looking Ahead--Corn And Dry Soils At Planting In 2012

What's the effect of dry conditions on potential yield? Here's a look ahead to 2012 crop season and some corn management practices to consider.

Dry conditions have been persisting in many parts of Iowa this winter. Modeling tools (computer programs) that simulate dry conditions at planting time can help us understand the effect of dry conditions on potential corn yield. The corn simulation model, called Hybrid-Maize, can address several questions regarding corn management practices. Iowa State University Extension corn agronomist Roger Elmore ran some possibilities through that computer program and came up with the following information and recommendations.

The first section of the following article is titled Part I: Yield prediction with dry conditions at planting. The second article is Part 2: What hybrid maturity changes should you make in 2012? The third article is Part 3: Should you make changes in plant population? All three articles were written by Roger Elmore and they follow here.

Part 1: Yield prediction with dry conditions at planting time

Dry conditions persist in many parts of Iowa. As of Jan. 30, 2012 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 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.

Simulation results: 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.

If soil moisture isn't replenished by planting time, yields will be reduced at many locations

We all know that many things can happen between now and planting. If soil moisture conditions do not improve by planting time, 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 by Roger Elmore, which is titled "Long silks, short pollen,... long year" and was presented in January 2012. Slides from that presentation with more detail are available here: CAS Presentation Slides.

Part 2: What hybrid maturity changes should you make in 2012?

The Hybrid-Maize model allows users to change soil moisture conditions at planting to simulate different possibilities. This capability allows us to simulate conditions with only half field capacity at planting.

Dry conditions persist in many parts of Iowa we explained above, in Part I of this article. 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.

What if it is dry at planting in 2012, should you consider planting an earlier-season hybrid?

As in the previous article (Part 1) in this series, I used a corn simulation model (Hybrid-Maize) to answer this question. 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?"

I compared two moisture levels: "A" which is 75% field capacity (FC) in the topsoil (0-12 inches) and 100% FC in the subsoil (12-40 inches), and "B" which is 50% FC in both topsoil and subsoil. I realize many soils now are drier than 50% FC so the second possibility may be overly optimistic for those areas. Other inputs for each site modeled are provided in Table 1 (with the exception of hybrids). Factors that varied across locations such as soil textures are shown in Table 2 (see Table 1 and 2 in Part I article).

Given the two soil moisture situations at planting discussed in Part I, the model allows us to simulate the effects of changing hybrid maturities. It assumes a generic hybrid and models corn growth based on temperature, solar radiation and precipitation actually recorded in the weather database for each research farm. I used two hybrids at each location: a full-season and an early-season hybrid. The full-season hybrids at the Northwest (NW) and Northeast (NE) locations required 2500 GDD (about 105 days RM) while the early-season hybrid required 2400 GDD (about 100 days RM). At the Central, Southwest (SW), and Southeast (SE) locations, the full-season hybrids required 2600 GDD (110 days) and the early-season hybrid required 2500 GDD (105 days).

Simulation results: At four of the five locations, modeled yield of full-season hybrids were greater than those of early-season hybrids in both soil moisture situations (Table 4). However, at NW, early-season hybrids out-yielded full-season hybrids in about half of the years (54% of the years with moist soils and 50% of the years with dry soils).

It is interesting to note though that in the years where full-season hybrids yielded more than early-season hybrids, the yield advantage was much greater than in the years where early-season hybrids yielded more than the full-season hybrids. This was true at all locations and with both soil moisture scenarios.

Interestingly, yield estimates for early- and full-season hybrids were consistent across both planting situations, whether soils were relatively moist or dry. The probabilities of either of the hybrids performing well were similar whether soils were moist or dry at planting.

The analysis shows clearly that hybrids of both maturities should be grown. This will spread risk and maximize yields over years.

These simulated data results mirror actual yields obtained from the ISU/ Iowa Crop Improvement Association's 'Crop Performance Test - Corn. These tests are conducted annually at twenty or more locations each year with a full-season and an early-season hybrid trial at each site. Means of the two trials in any specific region are usually similar. Again, this suggests planting both early- and full-season hybrids are important to maximize yields while spreading risk.

Summary: 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, as before, let's hope for complete recharge of our soil before planting.

Endnote: The articles in this series summarize portions of the 2012 Crop Advantage Series (CAS) talk entitled "Long silks, short pollen, …a long year" presented in January 2012. Presentation slides with additional detail related to this article are available at CAS Part II slides.

Part 3: Should you make changes in corn plant population?

What if it is dry at planting in 2012, should you consider lower plant populations? This factor is considered in simulations using the Hybrid-Maize computer model.

Dry conditions have been persisting in many parts of Iowa this winter. In areas of the Corn Belt with poorer soils and/or reduced rainfall, farmers typically reduce plant populations to compensate for the conditions. Is that something we should consider in Iowa if conditions remain dry at planting in 2012?

What if it is dry at planting in 2012, should you consider lower plant populations?

As in Part I and II of this series of articles, I used a corn simulation model (Hybrid-Maize) to answer this question. As mentioned, 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. I compared two scenarios: 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 (with the exception of plant population). Factors that varied across locations such as soil textures are shown in Table 2. (See Part I for Tables 1 and 2).

Given the two soil moisture scenarios at planting, the model allows us to estimate the effects of changing plant populations on simulated yield. As mentioned in the other two parts of these articles, the model assumes a generic hybrid and models corn growth based on temperature, solar radiation and precipitation actually recorded in the weather database for each research farm.

For this comparison, I used a single hybrid at each location: Northwest (NW) and Northeast (NE) locations: 2500 GDD (about 105 days RM); Central, Southwest (SW) and Southeast (SE) locations, 2600 GDD (110 days). The major change in these simulations from that discussed in Part I of these articles is that 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.

Simulation results: Yield estimates were consistent across both scenarios for soil moisture at planting for the three plant populations. That is although estimated yields were often greater when planting occurred with moist soil versus dry soils (we talked about this in Part I), the population effects were relatively consistent across both soil moisture scenarios (Table 5). In most cases, the number of years and the specific years where the higher plant populations were superior to the lower plant populations were the same in both soil moisture scenarios.

Table 5 displays the number and percentage of years where the lower of two plant populations increased simulated yields for the two soil moisture at planting scenarios. In all cases, with moist soils at planting, the lower plant population resulted in higher yields more often than if soils were dry at planting.

Locations varied in their responses. At the SE research farm near Crawfordsville, with dry soils at planting 32,000 ppa increased yields over those of 37,000 ppa one-third of the time. With wet soils at planting, in all but one year (1997) 37,000 ppa increased simulated yields over 32,000 ppa. Lower plant populations in NW and SE Iowa have a greater probability of resulting in greater yields that higher plant populations if soils at planting are dry than in other parts of the state.

The modeled yields show that higher plant populations improve the chances for higher yields in high-yielding years (see figures linked in the endnote). 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: Planting to achieve high corn plant populations is a good approach

As mentioned in the other articles in this series, we all know that many things can happen between now and planting. If soil moisture conditions do not improve – that is 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 (see information on typical plant population responses). Meanwhile, as before, let's hope for complete recharge of our soil before planting!

Endnote: This article and the two associated with it summarize portions of the 2012 Crop Advantage Series (CAS) talk entitled "Long silks, short pollen, …a long year" presented in January 2012. Figures presented at CAS provide more detail and are available here: CAS Part III slides.

 

 

 

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