September 29, 2004
Finding Safe Levels, Times for Applying Manure to Growing Crops
LINCOLN, Neb. — Applying manure to crops through center pivots could save time and labor, and fertilize crops when they need it. But salt in manure can damage plants so farmers need to know how much is too much.
To find out when and how much swine manure can be safely applied to corn and soybeans, University of Nebraska scientists conducted experiments at the Haskell Agricultural Laboratory near Concord.
While the effects of salt accumulations in soil are well studied, this Institute of Agriculture and Natural Resources research focused on salt's effects on growing crops, said Soil Scientist Charles Shapiro.
He teamed with IANR Irrigation Engineer Bill Kranz and Agronomist Charles Wortmann on this research.
"Lots of producers already apply manure to fields through a center pivot," Kranz said. Growing season applications would save time and money.
"Farmers want to know when and how much manure they can put on their crops before the salt in manure would be toxic to the plants," Shapiro said.
Researchers applied manure through a custom spray system that simulated pivots but allowed different application schemes on small test plots.
They checked manure's salt content using simple electrical conductivity, or EC, meters. Higher readings mean more salt.
Liquid manure from a pit was applied to corn and soybeans in early or late July at three concentrations. Some plots received undiluted manure with an EC of 20, some got a 50-50 water-
manure mix with an EC of 12 and others received a mix of 75 percent water-25 percent manure with an EC of 6.
These concentrations are higher than farmers typically apply but scientists wanted to identify the upper safe application limits for growing crops.
"In the earlier soybean applications, we severely damaged the plants at the high (concentration) rate," Shapiro said. "In the later stages, we stunted and defoliated the plants, but there was regrowth and survival, and there were much better yields" than with early or heavier applications.
Early full-strength application killed three-fourths of soybeans and some corn. Later application was less damaging to corn.
The EC 12 application in early July stunted soybeans, yellowed leaves and reduced leaf area. In corn, effects were less severe.
Corn yields improved 4 percent and 13 percent for early and later EC 6 applications, respectively. Soybean yields decreased 10 percent and 1 percent for early and later EC 6 applications, respectively.
Researchers concluded that manure with EC values of 6 or less should be safe for corn and soybeans at all growth stages. EC values of 12 should be safe for soybeans and corn by late July.
Applying manure through a pivot has several advantages over hauling it to the field in fall or spring, Shapiro said.
"It's better for the crop to use the nutrients in manure right away. It also greatly reduces chances they'll leach into the groundwater."
Pivot manure application also is less expensive and more uniform, Kranz said.
"If you use a wagon, which would be in the 2,500- to 3,000-gallon capacity range, you're looking at 566 loads compared to one round with the center pivot at a half-inch application," he said.
Nebraska Pork Producers help fund this IANR Agricultural Research Division research.
9/29/04-SA
Bill Kranz - Ph.D.
Biological Systems Engineering
Associate Professor
(402) 370-4012
Charles S. Wortmann - Ph.D.
Agronomy & Horticulture
Professor
(402) 472-2909
Charles Shapiro - Ph.D.
Agronomy and Horticulture
Professor
(402) 584-3803
Sandi Alswager Karstens IANR News and Photography (402) 472-3030
Department: Biological Systems Engineering
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