Released: June 08, 2001

Bring On The Sun, Agronomist Says
Newly-Seeded Crops Need Warm Weather

MANHATTAN, Kan. – A cool, wet spring replenished soil moisture through the nation’s heartland, but also complicated an already-dicey situation for soybean growers, a Kansas State University agronomist said.

"It was important to have enough rain to replenish soil moisture supplies after last year’s drought, but the soybeans have just not been growing very well because of this cool, wet weather," said Dale Fjell, crop production specialist with K-State Research and Extension.

Stands have been lost because of poor root development - and in some eastern areas, drowned out - to the point that some growers will have to evaluate fields and decide if they should over-seed existing stands or replant.

The situation has been made more difficult this year by a lack of high-quality seed, owing to last year’s drought. Good growing conditions were needed to get those poorer-quality soybean seeds off to a good start, but this spring’s conditions have fallen short, Fjell said. And seed availability for over-seeding or replanting also is still a problem.

"If a grower has three plants per row foot in 30-inch rows, that’s 50,000 plants per acre. That’s probably enough to leave the field alone," the scientist said. "If you don’t have that, you might consider over-seeding. If the rows are wide enough, you might be able to split the rows or plant at an angle to the existing rows."

Corn growers are facing similar issues.

"In areas where flooding has occurred and stands are lost, the question is, do we replant with corn or it is too late?" Fjell said. "Most fields treated with herbicides for corn can’t go to soybeans or sunflowers, and some can’t go to sorghum."

Over-seeding a poor corn field is not an option as it is in soybeans. Varying corn heights would make development and harvesting too difficult, he said.

"So producers have to decide if it’s necessary to replant. If you have 12,000 to 15,000 plants [per acre] on 30-inch rows out there, you probably have enough to keep it," Fjell said. "But if the plant population is at the low end of that, the open areas make the field more susceptible to weeds. Growers can use a post-emergent herbicide, but if they’re looking at a poor stand to start with, they may be reluctant to spend the money on herbicides."

For those facing the need to replant fields or parts of fields to corn – it’s not too late. Growers should look to varieties that mature more quickly, however, such as 100- to 105-day-maturing varieties.

To determine plant population in a corn field, count the number of plants in a 17-1/2-foot row and multiply the number by 1,000 to come up with the number of plants per acre, he said. For example, if there are 15 plants in a 17-1/2-foot row, that would equal 15,000 plants per acre. The process should be repeated in several places in the field, with numbers averaged to estimate the whole field’s population. Fjell also recommended a Bt hybrid because late-planted corn is more susceptible to corn borers.

Cool, wet weather has also curbed the sorghum crop’s development in parts of Kansas.

"There’s some purpling of the [sorghum] leaves because of the cool weather," he said. The discoloration is a sign that the plant has taken up less phosphorus from the soil than it should. However, with a few warm, sunny days, the crop would recover.

Unlike some crops, thin sorghum stands will compensate somewhat by growing extra tillers if the weather improves.

"But if you’ve lost sorghum stands because of the weather, you can still replant. The planting window is fairly large for sorghum – really up to the first week in July," Fjell said. "If you have less than 15,000 plants per acre, you might consider replanting."

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Mary Lou Peter, Communications Specialist
mlpeter@oznet.ksu.edu
K-State Research& Extension News