How Thick Should I Plant My Corn? What are other farmers doing?

Farmers continue to increase corn plant populations in Wisconsin and the U.S. Midwest. Every year as part of the Objective Yield Survey, the USDA-NASS counts plants in September at 150 locations in Wisconsin. Similar data collection is done in other corn producing states of the U.S. Midwest. Corn plant density in Wisconsin during 2018 was the highest ever measured at 30,650 plants/A. In 2018, Illinois had the highest plant density at 32,000 plants/A, followed by Iowa (31,100) and Minnesota (30,900).

In 1982, corn plant density ranged from 19,400 to 22,200 plants/A. Minnesota has consistently had higher average corn plant density than other states (Figure 1). In Wisconsin plant densities were 20,300 plants/A in 1982. Plant density has since increased at the rate of 267 plants/A*yr. Iowa and Illinois have had the greatest rates of change at 308 plants/A*yr.

Figure 1. Corn plant density changes over time for states in the U.S. Midwest Corn Belt. The rate of change (slope) in plants/A*yr since 1982 is reported for each state. Data derived from USDA-NASS.

Adjusting plant density for your fields is one of the key production decisions for producing high yielding corn. Clearly farmers are adjusting plant densities higher. Farmers still have numerous questions about plant density including:

1. What plant density achieves maximum yield (MYPD)? 
2. What plant density achieves the economic optimum (EOPD)? 
3. Are the MYPD and EOPD the same for grain and silage?
4. Do hybrids differ for MYPD and EOPD?
5. Do fields differ for MYPD and EOPD?
6. How does risk change, especially during years of drought or lodging?
7. What happens to plant bareness?
8. Do precision farming variable rate technologies make a difference? 

Over the next few articles we will try to address some of these questions.There is likely no standard recommendation for achieving MYPD or EOPD given that hybrid, environment, and economics (grain price and seed price) affect these measures. Rather MYPD and EOPD are moving targets where if we can get to within 95% of these values, it might just have to be good enough.

One approach that might be useful for your farm is to plant fields with a target plant density based upon your experience. Then for one round (or pass) in a couple parts of the field, increase plant density 10% (Figure 2). If harvest yield is affected, then adjust plant density the following season. If not, you are out the difference of ROI for seed.

Figure 2. An example of using reference strips for testing maximum yield plant density. Plant most of field to plant density based upon experience. In one strip (ideally 2 or 3) increase plant density 10%. Measure yield at harvest.

Brown Midrib and Leafy Corn Silage Performance + A New BMR Economics Calculator

Commercial corn hybrids grown in Wisconsin are often marketed to dairy farmers as "silage-specific." In the UW Corn Performance Evaluation Trials, conventional hybrids have similar yield and quality as bio-engineered corn hybrids. However, we often see yield and quality differences between silage-specific "leafy", brown midrib (bmr), and conventional/bio-engineered hybrids. In addition, companies often market newer 3rd- and 4th-generation silage-specific hybrids implying that breeding progress has improved performance.

Brown midrib corn (picture above) has a distinctive brown midrib on the corn leaf. These hybrids typically have greater digestible energy in the stover (stalks and leaves). Leafy hybrids have 2-5 more leaves above the ear compared to conventional hybrids.

Figure 1 shows the relationship between Milk per Acre (yield) and Milk per Ton (quality) for bmr and leafy hybrids. In most years leafy hybrids tend to be average for Milk per Acre and below average for Milk per Ton. BMR hybrids tend to be below average for Milk per Acre and above average for Milk per Ton. For either hybrid type there does not seem to be a trend for newer generation hybrids.

Figure 1. Mean Milk 2006 relative performance of Brown midrib and Leafy hybrids in the UW Corn Performance trials. The origin is the overall average of all hybrids tested between 1995 and 2018 (N= 38,664 plots). BMR plot total= 623 and Leafy plot total= 1538. Difference = overall hybrid average – trial average, Code above symbol= Year

Both bmr and leafy hybrids have lower than average starch content compared to the overall mean of all hybrids in the trial ultimately affecting both yield and quality (Figure 2). Leafy hybrids have average ivNDFD, while bmr hybrids have above average ivNDFD.

Figure 2. Mean starch and ivNDFD relative performance of Brown midrib and Leafy hybrids in the UW Corn Performance trials. The origin is the overall average of all hybrids tested between 1995 and 2018 (N= 38,664 plots). BMR plot total= 623 and Leafy plot total= 1538. Difference = overall hybrid average – trial average, Code above symbol= Year

Many research reports have concluded that bmr corn silage increases milk production in cows. Our data consistently shows higher Milk per Ton, but lower Milk per Acre yield due to lower forage yield primarily due to grain yield. Since there is typically no premium paid for higher quality corn silage, I have often said, "Buy all of the bmr corn silage you can buy, but be careful about growing it on your farm." Breeding progress has likely improved silage-specific corn hybrids, but there is a corresponding genetic improvement going on with conventional and bio-engineered hybrids as well.

The BMR Corn Silage Calculator: What are the economic trade-offs for yield and quality?

To better understand the economic effect of bmr corn in dairy operation, Dr. Randy Shaver et al. have developed a spreadsheet that can be downloaded here and here. This MS Excel spreadsheet calculates milk production of brown midrib (BMR) corn silage hybrids versus conventional  hybrids. The spreadsheet calculates differences based cow herd size. Dr. John Goeser (Rock River Labs and adjunct UW faculty) has produced a video explaining how to use the spreadsheet here.