Variety selection is still possibly the most important management decision for your corn crop. Every year we evaluate well over a hundred corn varieties that range from 75-100 relative maturity (RM). Even in lower yielding years, there can be as much as 70 bu/a separating the highest and lowest yielding varieties in our trials. The question becomes, “which one do I chose for my farm/field”. There are many different ways to approach that question, and many different ways to answer it.

One of the first factors that people tend to use is RM. The theory is that the higher the maturity, the higher the yield potential. To see if this is true, we took 4 years of data from our corn variety trials (2012-2015), with 5 trials in each year, and compared the final yield with the maturity of the hybrid. The results varied by environment. At our Fingal location, we didn’t see any relationship between RM and yield. The strongest relationship was at Carrington, where we were able to determine that RM accounted for approximately 25% of the yield difference between hybrids. Even though that sounds low, you could think of it like this; if you had one hybrid yield 140 bushels, and another hybrid yield 160 bushels (a difference of 20 bushels), then RM would account for 5 bushels of that difference, while all other factors including trait package, drought resistance, aggressive vs passive variety, soil-type adaption, and others account for the other 75% difference.

Another way to look at that information is to look at the likelihood that each variety performed above average. Table 1 includes a breakdown of the percent of varieties that performed above average in Carrington at each RM. According to this, from 2012-2015, the RM that gave the best chance of success was a 90 day hybrid. Of course, harvest moisture starts to creep up at about an RM of 89. The bottom line is that RM is only part of the story, good hybrids can still be found at lower RM, and bad hybrids can be found at high RM.

Table 1. The odds of a particular relative maturity (RM) in corn yielding above the average for the trial and the moisture at harvest.

We also have ongoing work with corn plant populations. Table 2 is a summary of the yield results from 2012-2014. This a compiled data set from a range of varieties each year. The maximum yield is achieved at 36000 established plants per acre. However, there is no statistical difference between any populations between 28000 and 40000 plants per acre, and only 6 bu/a separating those values total. So, the optimum plant population during this timeframe occurred right around 28000 plants/a.

Table 2. Comparison of corn yields at each plant population, averaged across 3 years and 4 hybrids (RM 83-RM 90) each year.

Mike Ostlie
Research Agronomist