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Corn+Soybean Digest

Rotations On Trial

Time has, indeed, been on the side of a comprehensive and large crop rotation experiment in southwest Wisconsin.

It was in 1966 — long before sustainability became a buzzword — when several University of Wisconsin-Madison agronomists began their experiment at the Lancaster Agricultural Research Station where silt loams predominate.

In collaboration with the University of Minnesota, Iowa State University and the University of Illinois, the trials evaluated the profitability and sustainability of continuous corn with commercial nitrogen (N) fertilizer applications compared to alfalfa supplying the N in a rotation.

Involving about 168 plots, the research also examined corn-soybean rotations and nurse crops like oats and wheat.

The experiment is considered to be one of the longest continuous running crop rotation studies in the U.S., according to Joe Lauer, University of Wisconsin-Madison agronomist.

“So much of today's cropping research occurs over relatively short time periods like three to four years,” says Lauer. “With longer-term studies, you hope to gain more meaningful insights into different rotations.”

While numerous cropping rotations have been examined over the years, the lion's share of the research has dealt with about five to six different combinations of rotations, such as continuous corn for two years as a control, as well as a basic rotation of corn followed by soybeans or alfalfa.

More elaborate rotations involved: corn-soybeans-corn-oats with an alfalfa seeding; corn-corn-corn-alfalfa-alfalfa; and corn-corn-oats with an alfalfa seeding-alfalfa. Wheat was also sometimes substituted for oat seeding. Most rotations spanned a period of two to five years.

The trials also involved various tillage methods, such as moldboard plow, chisel plowing and strip-tillage. Strip-till generally produced the best growth and yield results in corn rotations.

In judging the trials, Lauer emphasizes that available government payments or conservation programs, as well as how they may influence cropping choices and the economic impact, were excluded.

“The ongoing trials have helped to validate the important role that crop rotations continue to play in promoting good soil management and long-term productivity and profitability,” he says.

“We're learning that in order to capitalize on the benefits of modern genetics, the practice of using N fertilizer and crop rotations must go hand-in-hand.”

As N prices rise or become more volatile, crop rotation will also become more important. For example, the trials at Lancaster showed that corn yields improved with more frequent rotation. The consistent winner in the Lancaster trials was a corn-soybean-corn-oats-alfalfa rotation.

In other trials using a continuous, three-year corn rotation and then two years of alfalfa, the first year of corn performed well; however, yields started to decrease subsequently.

“Unless you apply N at 100-200 lbs./acre, yields tend to remain rather flat over time in a continuous corn or a corn-soybean rotation,” explains Lauer.

For example, even at 200 lbs. of N/acre, continuous corn yields increased only 0.9 bu./year.

However, the corn yields increased 1.4-1.6 bu./acre/year in extended rotations using 100-200 lbs. of N/acre. That compares with yield increases of 1.1-1.3 bu./acre when N applications rates were below 100 lbs./acre.

The trials also showed that corn yield decreased about 10% with second-year corn and another 5-7% with third-year corn. After the third year of continuous corn, grain yields didn't change much more.

Yet, relying solely on N fertilizer doesn't overcome everything in the quest to get the best yield rate over time, according to Lauer.

“The trials are telling us that N applications — when combined with longer-term crop rotations — will consistently generate better yield results,” says Lauer.

Longer-term rotations also improve water infiltration, soil compaction, organic matter and plant nutrient availability.

“There's no magic bullet out there that will solve all the problems in trying to boost yields; however, utilizing good crop rotations can play a key role in reducing some of the risk and in sustaining good yields over time,” says Lauer. “What's good for the soil will ultimately be good for the pocketbook.”

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