Wallaces Farmer

For crop rotation decisions, consider field selection, compaction, residue management and soil fertility.

Rod Swoboda 1, Editor, Wallaces Farmer

January 28, 2008

5 Min Read

On some fields, farmers are still deciding whether to plant corn after corn, soybeans or other crops following corn. Agronomy experts say the most critical decisions begin with analyzing highly productive fields, managing crop residue and soil compaction in those fields and maintaining soil fertility.

The trend toward corn after corn has been underway since grain prices moved higher in late 2006. Last year, U.S. growers planted a record 93.6 million corn acres, an increase from 78.3 million acres the previous year. Though the seed industry is predicting a decrease in corn acres for 2008, corn acreage is expected to remain at relatively high levels.

Choose right crops for the right fields

"For farmers who are still looking at crop rotation options, those choosing corn after corn should start by selecting fields that historically have higher corn yields, good drainage and medium-textured soils with ample water-holding ability," says Paul Gaspar, an agronomy research scientist with Pioneer Hi-Bred. "Seedbeds need to be in top shape to handle the growing season challenges, no matter which rotation plan is in place.

"At planting time corn-after-corn fields present a more adverse environment for the corn seed and seedling. It's difficult to wait, not knowing what the weather forecast holds," says Gaspar, "But don't plant corn-after-corn fields too early - keep the planter out of the field if soils are below 50 degrees and warmer weather is not in the forecast."

Wet fields also can cause problems. Surface compaction, sidewall compaction and/or deep compaction can restrict root growth and limit water uptake and yield, particularly if followed by drought conditions.

"Managing residue from the previous crop is also a key factor for a good start in 2008," says Gaspar. "Corn produces more than twice the amount of residue as soybeans. Excessive corn residue can result in much cooler soil temperatures and higher soil moisture at planting and can be a concern no matter which crop is going into the ground this spring. The goal is to clear residue from the row area - potentially with row cleaners, coulters or other residue management attachments on the planter. These can help with more rapid germination and emergence, particularly if there were challenges in distributing residue evenly during harvest."

Consider soil fertility in crop rotations

In looking at crop rotation choices, soil fertility should be based on thorough soil testing and local Extension recommendations. Soil tests are needed to determine soil pH and existing levels of phosphorous and potassium. Soil pH should be at or above 6.2 for growing corn. If planter attachments are available for applying starter fertilizer, you should consider applying appropriate rates of nitrogen, phosphorus and potassium at planting time. This will improve the uniformity and speed of emergence of corn in cooler soils.

Corn residue ties up more nitrogen than soybean residue as it decomposes, so you should plan to apply about 50 pounds of additional nitrogen to corn after corn vs. corn-after-soybean fields.

"In high residue fields, consider using 50 pounds of starter nitrogen to give plants a faster start," says Gaspar. "In all fields, consider splitting nitrogen applications, if possible. This can reduce nitrogen losses and help ensure corn plants have adequate nitrogen throughout the season."

More corn on corn being grown now

Traditionally, growers have rotated fields in a combination of corn and soybeans or other crops. That trend continued until recent years, with the most significant change occurring in 2007. In the past, there was some concern of negatively impacting yield if rotation was not made each year, or in some cases, at least every few years. However, the latest hybrids are holding their own in agronomic terms through a combination of genetic improvement and crop management practices. Today's hybrids have better disease resistance, root systems and seed treatments, particularly compared with hybrids from just a few years ago.

Though corn-soybean rotations remain a stable production practice, there is no strong indication that it will continue to be the standard of stability. In fact, 2007 brought very positive signs for corn-after-corn production. Yield tells the story and results were favorable in 2007 for many growers. Larger farming equipment also has contributed to increasing corn-after-corn rotations. The time once required for corn planting has been reduced with the ever-increasing size of equipment.

Control rootworm in corn on corn

"Harvest data from the 'year of the corn' in 2007, will be of particular interest to growers," says Murt McLeod, another Pioneer agronomy research scientist. "With increased corn-after-corn acreage, last year was an optimum time to analyze data for hybrid performance and insect control. For unknown 2008 growing conditions, selecting hybrids that have a broad spectrum of insect control and strong root systems is the key.

"Corn rootworm larvae are one of the most destructive insects of corn in North America," says McLeod. "Feeding on the root system, damage from corn rootworms can affect standability and limit water and nutrient uptake in the plant, impacting overall plant health and grain development. The end result can be yield loss of 10% to more than 30% which is common with moderate to high corn rootworm populations in untreated fields.

"Though corn rootworm pressure was less this past growing season in several areas of the Corn Belt than the previous two years, research trials were good indicators of yield performance during lower pressure situations," says McLeod. "Higher yielding corn is still the overall goal for growers, and hybrids need to perform in all levels of insect pressure."

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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