In June 2009 no one in their right mind would have guessed farmers would harvest record corn yields last year. The spring was cool and wet, planting was delayed, and the season was simply of to a sour start. Yet that's what happened. Now Bob Nielsen, a Purdue University corn specialist, is probing why and how it occurred.
"Not all the factors that influence corn yield are negative," he notes. "There are positive factors too. Those may have come into play last year."
Two determining factors in grain fill that seemed to promote higher yields were number of kernels and weight of the kernels. There tended to be more kernels per ear and heavier kernels in most situations where environmental conditions were favorable last year, the corn specialist observes.
Harvesting more kernels per ear stems primarily from less kernel abortion during grain fill, he suggests. A longer grain fill period tends to be desirable, and it was longer than normal last year. That was a direct result of the cool weather during pollination and early grain fill across a good part of the Corn Belt, and especially across most of the Eastern Corn Belt.
"It's a balancing act," Nielsen says. "Cool weather makes for a longer grain fill period, and that's a plus. A warmer period means you get more food produced per day, and that's also favorable. But in cases of cool summers, the longer grain fill advantage seems to win out."
He notes that in 1992 and 2004, the same scenario played out. The 1992 season featured some days in July when you needed to wear a jacket in the middle of the day. Yet yields were way above trend yield. Corn was wet at harvest, however, just as it was this year for most people.
The test weight factor
Wherever Nieslen goes this winter and says that heavier kernels were one of the factors that contributed to higher yield, he immediately gets some stares, and usually a few hands popping up. Many people reported lower test weights this past fall. So how could kernels be heavier, contributing to higher yield, if test weights were lower?
Right up front, Nielsen stresses that the test weight issue is a can of worms, very difficult to explain and even harder to understand. "The truth is that test weight and how heavy kernels are just isn't the same thing," he explains.
Test weight is the amount of grain fitting in a standard measure, he continues. Size and shape of kernel, not just weight, can influence how many kernels fit into the measuring cup. Low test weight doesn't always indicate poor quality by itself. Instead, it depends what caused the low test weight in the first place.
"For example, if it's dry and you get low test weight, that's likely because protein was laid down first, then starch, and there wasn't as much starch laid in," he says. "So test weight is lower. But as far as feeding value, the protein content may actually be slightly higher, because there's a higher percentage of protein in each kernel than if the kernels filled up with starch as in a normal year."