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3/23/2009 - 3/29/2009

Corn Nitrogen Rate Calculator Update

by John Sawyer, Department of Agronomy

Nitrogen (N) Response Trials Added
The Iowa Nitrogen (N) response trial database was updated March 24, 2009. Response trials were added from 2008 research and several trials from older research were removed. There are now 176 trials for corn following soybean and 78 trials for corn following corn. Being able to easily update the database with recent data is one of the many advantages to this dynamic approach for corn N rate guidelines. Having new response trial data allows rapid updating with changing hybrid genetics, rotations and climatic conditions.

With the updated database, calculated N rates have changed only slightly from last fall. The table below gives the N rate at the maximum return to N (MRTN) and the profitable N rate range from the updated calculator for several N:corn grain price ratios. You can work with any price of N and corn you wish when running the calculator. Output information includes the N rate at the MRTN, the profitable N rate range, the net return to N application, the percent of maximum yield, and the selected N fertilizer product rate and cost.


What is the Corn Nitrogen Rate Calculator?
The Corn Nitrogen Rate Calculator Web tool is a resource that aids N rate decisions for corn production and is helpful in determining the effect of fertilizer and corn price on application rates. The method for calculating suggested N rates is based on a regional (Corn Belt) approach to N rate guidelines. Details on the approach are provided in the regional publication Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn. This approach and the Corn Nitrogen Rate Calculator are now being used by seven Corn Belt states: Iowa, Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin; with Michigan and Ohio being added this year.

corn nitrogen calculator chart


Resources for N Rate Decisions
The Corn Nitrogen Rate Calculator Web tool is located at

The regional publication Regional Nitrogen Rate Guidelines for Corn, PM 2015, can be ordered through any ISU extension county office, on the Web through the extension online store , or by calling (515) 294-5247. An electronic copy of the publication is available at

The ISU Agronomy Extension Soil Fertility Web site is located at


John Sawyer is professor with research and extension responsibilities in soil fertility and nutrient management.

Tips for Managing Corn Residue in Continuous Corn

By Mahdi Al-Kaisi, Department of Agronomy and Mark Hanna, Department of Agriculture and Biosystems Engineering

Many farmers planning for continuous corn this season are having spring tillage questions because wet conditions and late harvest in many parts of Iowa delayed tillage operations last fall.  Farmers now want to know how to approach managing the corn residue, given the potential wet soil conditions and subsequent delay getting to tillage operations this spring.

There are many good management options for farmers who are considering continuous corn. However, conventional tillage as a method to manage residue, especially in wet soils, is not one of them. Tilling soils with high moisture can result in:
• significant soil compaction,
• an unsuitable seed bed where large wet and un-shattered soil clods will form,
• side-wall compaction due to smearing of the soil causing less than ideal conditions for root development,
• and the potential of inducing K deficiency due to soil compaction.

To avoid these potential problems, which can have significant impact on crop performance and ultimately yield, alternative options can be considered in managing heavy residue in continuous corn. These management options depend on soil type and soil moisture conditions.

Loess soils
If soil stays somewhat wet in the top 2 – 3 inches, farmers should consider no-till planting with the planter only, particularly in western Iowa loess, but also generally in other well-drained or somewhat well-drained loess soils outside the Des Moines glacial-till soils lobe.  It is always a good management option to have row cleaners on the planter and available for use in corn-after-corn. However, be prepared to raise row cleaners out of the way if wet residue wraps on them. .

Glacial-till soils and bottomland soils
If soil stays wet in the glacial-till soils and on bottomland soils in other areas with poor drainage and higher clay content, run the planter empty with row cleaners to move residue aside. This option removes the residue and exposes the soil surface without excessive tillage compaction and soil smearing. Letting the land dry for two to three days prior to planting will help speed up water evaporation and warm up the top 2 – 3 inches; this is sufficient depth to ensure corn seed germination. Research documents that the use of row cleaners to remove residue prior to planting in wet soil conditions is very effective in improving corn germination.
Many farmers may attempt to strip-till or disk wet soils this spring. However, this can be counter-productive as wet soil won’t shatter well and will likely compact, particularly with large tractor/implement loads. The temptation to ‘dry’ the soil surface with a disk, or field cultivator (if cornstalks don’t plug it) may result in compact soil clods in the surface planting zone. If conditions are wet at planting time, increasing the seeding rate by two to three thousand plants per acre may help compensate for any seed germination problems and associated stand loss.
Soil moisture content is very high in most of the state at this time, but there’s still a chance that things may dry out (at least on the surface). We will need warm, sunny, windy conditions between now and late April to make that happen. Generally, tillage in wet soil conditions in any cropping rotation system is not the best choice. The disadvantages are much greater than using a few equipment modifications to manage residue.


Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery.

March 23 Crops and Weather Update

By Doug Cooper, Extension Communications and External Relations

Iowa State University Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope and soybean agronomist Palle Pedersen stopped by the studio this week to visit about weather and crops issues.

Elwynn Taylor said dry fields gave way to wet fields as a series of storms moved through Iowa recently. The long term weather points at the possibility of a drier spring this year, and that, Taylor says, would be welcome news.

Rich Pope reported that traps are being set to collect black cut worm moths as they begin their trek from southern states into Iowa. The number of trapped moths will help farmers determine the need to take preventive action against the potential pest.

Extension soybean agronomist Palle Pedersen is hoping for improved weather this spring and not a return to last year's weather patterns. He says farmers will have some additional variety choices this year, a couple that he believes look promising.

This article was published originally on 3/30/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.