For the past three years, Larson notes, there has been a cluster of National Corn Growers Association irrigated yield contest winners in northwest Texas, Colorado, and western Kansas, where yearly rainfall averages only 14-18 inches, “showing that corn can be very productive in a dry area.”

Five of the six high yields were produced under center pivots.

“We typically expect lower yields from center pivot-irrigated fields,” he says, “but those growers are achieving very high yields under pivots. There are some advantages to growing corn in that system, and I think we could benefit from incorporation of new technology in our center pivots that would allow our corn to be a lot more productive.”

One of the contest winners in southeastern Colorado, Larson says, used furrow irrigation on a 10-14 day schedule, “which is considerably more lengthy than the schedule we typically follow.”

Curious as to why that cluster of contest-winning fields was so productive, he says, “I looked at average daytime and nighttime temperatures for the region during the first 10-15 days of July, when their corn was going through its early reproductive stage, and for Mississippi’s crop during the same stage.

“They’re actually hotter in the daytime during pollination than we are, but our nighttime temperatures are a lot warmer than theirs, and that’s a big drag on our corn because it increases respiration rate — burning up energy that could be utilized to produce higher yield. That was a critical limitation for us in the last two years.”

Looking at historical June nighttime temperatures in Mississippi from 1996-2011, Larson says, “Three seasons jump out — 2010, and 2011, with reduced productivity and lower irrigated corn yields, and 1998 with its poor yields and aflatoxin problems.

“While we’ve made a lot of improvement in terms of hybrid adaptability for our region, which has allowed us to produce more consistent yields, there’s no doubt the high nighttime temperatures the last couple of years have caused a considerable yield drag on our irrigated corn.”

There is, he says, “a lot of talk about pollination problems — and when we have a pollination failure, it can indeed be catastrophic — but I don’t really see a lot of pollination issues in our corn. Rather, a lot of the yield loss I see comes from kernel abortion due to low photosynthetic rates, high respiration rates, and the plant not having adequate energy resources to fill all the kernels on the ear that it potentially can.”

If there were pollination issues, Larson says, “we’d be seeing spots on the ear where kernels aren’t filling. But mostly what we’re seeing is kernels failing to develop out on the tip of the ear because the plant doesn’t have what it needs in its ‘gas tank’ at that particular time to fill those kernels.

“The corn plant is very dependent on photosynthetic rate and respiration rate during the first 20 days following pollination. During tasseling it can have a full tank of energy built up in its vegetation, but the problem is that when kernels pollinate and begin to develop, they’re extremely small, and they have basically zero competitive ability to draw that energy away from the vegetation, particularly during the short time period when kernel number is determined.

“If we have stress conditions, however mild they may seem — from cloudy weather, too much or too little water, nutrient deficiency, high temperatures — it can reduce photosynthetic rate, and any reduction in photosynthetic rate, particularly during the first 10-20 days after pollination, is going to reduce kernel numbers. From milk stage (roasting ear) on out, basically all you’re doing is building kernel weight.”