Increasing production Light interception key to corn yields

Corn acreage nationwide reached 50-year records in 2007, and the Southeast was no exception. The dramatic drop in cotton acreage in the Carolinas and Virginia was accompanied by steep increases in corn.

Despite prices that remained high, a planting time freeze, followed by one of the worst droughts on record replaced optimism with desperation for many growers banking on high priced, high profit corn.

What 2008 brings remains to be seen, but it is clear growers in the upper Southeast learned some harsh realities of corn production in 2007.

“Let's not miss the signals, the game today is all about high yields. The market wants grain, and the grower needs to think about high yields. The days of trying to figure out how to manipulate things to stay in the ball game are over. We now need to focus on how we can get another bushel or two out of that field,” says long-time North Carolina Corn Specialist Ronnie Heiniger.

Speaking at the recent North Carolina Agricultural Crop Consultants Association winter meeting, Heiniger says the plateau level of corn has jumped significantly in North Carolina and across the country.

Among the many reasons for this jump in yields is the use of Bt corn. Not because corn borer is a big yield issue, but because it is tied into the ability of corn to trans-locate sugars to the growing point. Heiniger explains that the strength of the ability to acquire carbon has changed because of the Bt factor in the corn plant, which makes a difference in how to manage the crop and directly impacts yield.

While technology, like the onset of Roundup Ready and Bt corn, are important to achieve higher yields, the real increases are more likely to come from managing three things — light, water and nutrients.

“Despite nationwide increases in corn production, we are not where we need to be yet — we have a ways to go. Many of our growers recognize this need to increase production, and as a result we are seeing more and more 300 bushel per acre corn,” Heiniger says.

“Less than 20 years ago corn specialists widely agreed that the maximum yield potential possible for corn was 350 bushels per acre. This past year, despite the drought and the freeze and all the other weather factors, we have an entry in the State Corn Yield Contest that tops 350 bushels per acre,” Heiniger emphasizes.

One of the keys to increasing yield is to eliminate all the other stresses and focuses on maximum use of sunlight. In 2007, the one thing growers had plenty of was sunlight. As a result, Heiniger contends, we shouldn't be surprised that growers who reduced moisture stress with irrigation and other stresses by other means would get very high yields.

Row spacing and plant populations are the two ways growers can manage light interception in corn — or other crops. The key is to manage light based on other stress factors in a field, according to Heiniger.

In too many cases growers lose light by having too wide row spacings. In these cases, light contacts bare ground between rows, which is light lost to the crop. By going to a twin-row configuration, a grower can capture more of that light. Going to narrow-row spacings allows growers to capture even more light.

By manipulating row spacings, with narrow or twin-rows, a grower can dramatically impact corn production in a positive way, especially in young plants.

There is a correlation between corn plant height and yield. As the rows get narrower, the plants compete for light and they get taller, until they reach optimum height. Once the plant begins to compete for something other than light, the plants stop getting taller.

To get optimum yield, growers should be looking for the optimum balance between competition for light and minimizing competition for moisture and plant nutrients, according to Heiniger.

Row spacing influences the optimum balance early in the season in terms of intercepting light in the field. Later in the season there is no difference between narrow-rows and wider-rows. The early season influence on light competition will increase yields by about six percent from 36- to 30-inch rows and by another six percent from 30-inch to 20-inch rows, according to Heiniger.

The number of leaves a corn plant is able to produce is determined in the seed — the grower cannot increase leaf surface area. Moving plants around in different row configurations doesn't increase leaf area in the field. Stress can reduce leaf area in the field, but increasing light interception is minimally affected by early season light competition in narrow-rows, Heiniger says.

To significantly increase light interception, growers have to put more plants in the field. Once corn fields reach maximum plant populations, based on row spacings and plant spacings, a grower can increase the interception of light and have a chance to significantly increase yield, Heiniger contends.

In 2007, cotton production in some areas of North Carolina dropped as much as 50 percent with much of that acreage going into corn production. Unfortunately, cotton equipment is not typically set up for narrow-row spacings, reducing the chances of maximum corn yields. The high yield potential of modern corn hybrids was in many cases squandered by equipment restraints among growers switching from cotton to corn.

Thick canopied, late-maturing hybrids planted at low to moderate plant populations are still recommended for wide rows.

Getting the right corn plant population, regardless of the equipment used is a difficult task, but one that has a direct bearing on final yield. In work at Purdue University, Bob Nielson calculated just how much yield is lost from planting too high or too low plant populations.

Nielson says spacing uniformity can be measured by the occurrence of doubles or skips, or in terms of standard deviation. An absolutely perfect stand where every plant is exactly 7.25 inches, (28,840 plants per acre in 30-inch rows) from its neighbor would have a standard deviation of zero. If plants on average varied plus or minus two inches from the desired 7.25 inches then the standard deviation would be two.

Nielsen (Purdue University, Indiana) has conducted extensive investigations into the effects of plant spacing variability on final yield. He calculates that every additional one-inch of standard deviation decreases yields by 2.5 bushels per acre

Heiniger says there is a delicate balance between intercepting the optimal amount of light without losing ear size. Too many plants create stress via competition for water and other nutrients and reduces ear size.

The big question is, “how do you tell when you get too many plants in the field”. The key is uniform ear size, Heiniger says.

“In tests in the field with growers we can increase plant populations up to 40,000 plants and maintaining 62 percent of ear size, he adds. Reaching this optimum balance is different for every growers and even from field to field. For some producers 40,000 plants per acre is not high enough, while 27,000 plants is too high for others.”

“Plant spacing within the row is the key. Reducing or increasing the row width in corn is only to maximize plant spacing. For example, a 36-inch row spacing to get 38,000 plants requires a four-inch or less plant spacing within the row. Regardless of the row spacing, reducing plant spacing within the row to four inches or less is likely to reduce yield,” Heiniger says.

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