About Corn Split N

Contributors

Jeff Andresen, Larry Biehl, Seong Do Yun, Otto Doering, Roger Elmore, Ben Gramig, Pat Guinan, Beth Hall, Chad Hart, Ray Massey, Chris Panza, Dennis Todey, Molly Van Dop, Melissa Widhalm

Background

The Corn Split N decision support tool helps farmers and advisors understand the risks and benefits of using a post-planting nitrogen (N) application for corn production. This product combines historical weather data and fieldwork conditions with economic considerations to determine the feasibility and profitability of completing a second (split) N application within a user-specified time period.

Why Split Apply Nitrogen?

Farmers traditionally apply nitrogen to the soil in a single pass during either the fall or in the spring before planting. However, early nitrogen application can result in significant losses due to weather factors (e.g. warm, moist soils). Research has shown that a split application of nitrogen -- one application in the fall or around the time of planting and a second application after planting when there is the greatest demand for N from the crop -- can reduce total nitrogen use (savings to the farmer) and/or reduce nitrogen loss to the environment (savings to society).

There are some risks involved with a split nitrogen application strategy. Greater costs are incurred because two passes through the field are required. Additionally, the second application (if conducted using ground application equipment) may be hindered due to weather conditions. If soils are too wet during the time when a second application of nitrogen is needed, insufficient nitrogen may result in lower yields. With the Corn Split N tool farmers now have a way of quantifying the costs and benefits of post-planting nitrogen applications.

Split Nitrogen Timing and Application Methods

University recommendations suggest applying N by V6 if you do not use a starter N. If starter N is used, the post-planting application is determined by height of the corn plant and equipment used. For typical surface application equipment, application by V8 is recommended. Some surface application equipment may be able to apply N until V10. Split nitrogen application can also be conducted using aerial application. The Corn Split N tool is intended for use with surface application equipment.

Nitrogen management of corn includes many factors, one of which is the timing of application. Recommended application times vary depending on the climate and soil conditions of your location. This tool is designed to assist farmers with planned sidedressing of nitrogen.

Planned split N applications are different than rescue N applications. Rescue N is for the purpose of remedying a known problem of insufficient N in growing plants. It may occur early enough for surface application of N or so late that aerial application is the only option. Planned split N applications are done with the intention of supplying sufficient N without waiting for the crop to express a need. By that time it may be losing yield.

The Corn Split N tool helps farmers investigate the implications of planning a post-planting sidedressing of N. Research indicates that split N applications have several potential benefits. First, the total amount of N needed for optimal yield may be lessened. Fertilizer savings are most likely to be experienced where the risk of N loss is high. Second, increased yield may occur. Research results differ on whether or not yields can be increased. In some years, split N applications increase yields and in others it does not.

If a farmer plans to apply nitrogen post-planting and is unable to accomplish this due to weather or equipment problems, there is a good chance that yields will suffer. This tool estimates how often that will occur given your described equipment complement.

Fact Sheets and Tutorials

Corn Split N_DST User Guide

Data Sources and Technical Details

The Corn Split N tool combines historical weather data, historical fieldwork data, and economics to determine the riskiness associated with post-planting nitrogen applications for your location.

Corn Growth Estimates

Corn height is an important factor in determining the probability of successful post-planting nitrogen application since your equipment must be able to travel through growing corn without damaging it. The Corn Split N tool provides estimates of corn development stages based on your location, your selected planting date, and the accumulated corn growing degree days (GDD) for the year.

The Corn Split N tool uses daily gridded growing degree days (GDD), calculated using the 86/50 method, as a proxy for corn height. Gridded data are derived from nearby weather observation stations, which allows data to be available for the entire region at about a 2.5 mile resolution. GDD are based on data from the Applied Climate Information System (ACIS). The relationship between accumulated GDD and plant growth comes from recommendations found in ISU publication PMR 1009 entitled “Corn Growth and Development.” Corn emergence in the Corn Split N tool is assumed to occur at 105 GDD post planting, although the scientific literature states emergence can occur at 90-200 accumulated GDD post planting depending on factors such as ground cover and tillage practices.

GDD accumulations and associated corn growth beyond the current day are estimated based on the 30-year (1981-2010) average GDD accumulation for your location.

For additional information about estimating corn growth please see the following references:

• - Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. "Corn Growth and Development" PMR 1009. Iowa State University Extension, Ames, Iowa. Available online at https://store.extension.iastate.edu/Product/Corn-Growth-and-Development
• - Nielson, B. 2014. "Use Thermal Time to Predict Leaf Stage Development In Corn" available online at http://www.kingcorn.org/news/timeless/VStagePrediction.html
• -Hall, R.G. (date unknown). "Corn growth stages with estimated calendar days and growing-degree units" available here. R.G. Hall is an Extension Agronomist with South Dakota State University, Brookings, SD.

Historical Field Work Data

The Corn Split N tool uses historical observations (1981-last year) and model simulations of days suitable for field work (FWD) to estimate the probability of being able to fertilize corn during the user-defined application period. FWD are simply the estimated number of days per week that are suitable for conducting in-field activities.

Observed FWD data are reported weekly by the USDA National Agriculture Statistics Service (NASS) throughout the growing season (roughly Mar/Apr - Oct/Nov) for each Crop Reporting District (CRD) in the following Corn Belt states: IA, IL, IN*, KS, MO. You can view maps depicting CRDs for each state here.

*NOTE: Prior to 1995, Indiana FWD data were reported on a 10-day interval. These data have been converted to a 7-day interval based on the average field work days per day in the reporting interval. For example, if 10 days were suitable for field work in a 10-day reporting period this is 1 work day per calendar day. This conversion process is imperfect, but results in a daily moving average over the entire growing season and allows for the data to be assimilated into a weekly time-step consistent with all other state data.

In Michigan, Minnesota, Nebraska, North Dakota, Ohio, South Dakota and Wisconsin the FWD data reported by NASS are only available at the state-wide level (i.e. one weekly value represents conditions for the entire state). The Split N tool requires more localized FWD data. Therefore, the weekly FWD values for these seven states within the Split N tool are estimated weekly values, not historical observations. The estimates are derived from the statistical relationship between historic weather data and the area-weighted soil drainage class for each CRD in the states where weekly FWD data are available. This is the empirical equation used to generate these estimates based on observed data for the years 1980-2010:

Estimated field workdays = -5.56285 + 0.210292*(average maximum temperature) -0.00237*(average maximum temperature squared) -0.23367*(average minimum temperature) -0.00251*(average minimum temperature squared) +0.005212*((average maximum temperature)*(average minimum temperature)) -1.12549*(total precipitation) +0.113922*(total precipitation squared) +0.055012*(average maximum temperature the previous week) -0.03594*(average minimum temperature the previous week) -1.01346*(total precipitation the previous week) +0.00868*(precipitation in previous week)*(average minimum temperature in current week)) +0.021476*(annual time trend) -0.00025*(annual time trend squared) -0.45365*(spring indicator variable) +0.374839*(fall indicator variable) -0.42513*(winter indicator variable) +3.065181*(soil drainage class index) -0.43322*(soil drainage class index squared)

A Random Effects model with root mean squared error = 0.9989 was used to estimate the parameters in the equation above. All weather data are from the Midwestern Regional Climate Center, all soils data were processed from the SSURGO data from USDA-NRCS, and seasonal indicators are based on solstices and equinoxes assumed to occur on the 21st of March, June, September and December of each year.

Yield Penalties and Benefits

Corn plants require adequate nitrogen for optimal growth. In the event that plant-available nitrogen is limited, there could be an associated yield reduction. Conversely, a "rescue" application of nitrogen could result in a yield increase. The Corn Split N tool allows you to customize yield (bu/acre) penalties and benefits to account for these situations since they will vary by location and time of year.

The default values used for Yield Benefit and Reduced N are based on data reported in the literature. They do not take into account the range of values that could be used. You are encouraged to seek information from university extension or crop consultants on what values should be used for your particular soil and climatic conditions.

For additional information about post-planting N application and yields please see the following references:

• - Bundy, L.G. 2006. "Sidedressing nitrogen: Useful on all soils?" Proc. of the 2006 Wisconsin Fertilizer, Aglime & Pest Management Conference, Vol. 45.
• - Penn State Agronomy Guide (2013-14), Part 1 Section 4: Corn - Applying Fertilizers (page 66). Available online at http://extension.psu.edu/agronomy-guide/cm/sec4/sec44d.

The default yield penalties for most states covered by the Corn Split N tool are based on the “Percent of Maximum Yield” information contained in the online Corn N Rate Calculator that was jointly developed by agronomy and fertility extension specialists from across the Corn Belt region (J. Camberato, S. Culman, D. Kaiser, C. Laboski, E. Nafziger, J. Sawyer and K. Steiner. Corn Nitrogen Rate Calculator, 2013). The Corn N Rate Calculator is based on the publication “Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn” (Sawyer 2006). Detailed yield penalty data for individual states that are not covered by the Corn N Rate Calculator are described below.

Indiana yield response to Nitrogen fertilizer data by region and sandy soils were obtained from: R.L. Nielsen and J.J. Camberato. Indiana corn Nitrogen response trials, 2006-2014. Purdue University, West Lafayette, Indiana.

Kansas and Missouri

In the absence of data from Missouri, yield responses are based on the “Percent of Maximum Yield” information contained in the online Corn N Rate Calculator that was jointly developed by agronomy and fertility extension specialists from across the Corn Belt region (J. Camberato, S. Culman, D. Kaiser, C. Laboski, E. Nafziger, J. Sawyer and K. Steiner. Corn Nitrogen Rate Calculator, 2013). The values for Southern IL were used for MO.

Nebraska

Note: The corn yield response to Nitrogen data for Nebraska are based on irrigated trials only. Nitrogen response and the associated yield penalties from not applying all of the desired amount of N are not accurate for rainfed corn, and likely represent a lower bound estimate of the yield penalty for corn that is not irrigated.

All data on corn yield response from Nebraska are based on the data and estimations contained in the peer-reviewed journal article: A. Dobermann, C.S. Wortmann, R.B. Ferguson, G.W. Hergert, C.A. Shapiro, D.D. Tarkalson, and D.T. Walters (2011). Nitrogen response and economics for irrigated corn in Nebraska. Agronomy Journal, 103(1), 67-75. More details and nitrogen rate recommendations for corn are available from the University of Nebraska Cropwatch website: http://cropwatch.unl.edu/corn/soilmgt. Yield penalty data are not available for all soil textures on NE farms.

North Dakota

All data used in the SplitN tool for the state of North Dakota were provided by Dr. Dave Franzen, NDSU Extension Soil Specialist, and are based on the data that underlie the North Dakota Corn Nitrogen Calculator tool: https://www.ndsu.edu/pubweb/soils/corn/. This tool provides ND farmers with N rate recommendations based on location, prior crop, soil texture and tillage details.

South Dakota

South Dakota State University Extension Soils Field Specialist, Dr. Anthony Bly, provided all data used to calculate the default yield penalties in the SplitN tool.

Wisconsin

A default yield penalty is assigned based on the predominant soil properties in the user-selected county. The four available soil yield potential groups are based on soil property information from University of Wisconsin Soil Testing Laboratory (http://uwlab.soils.wisc.edu/a2809-soil-map-unit-info/). Yield penalties for the county default or user-selected yield potential group in Wisconsin are based directly on the data that underlies the multi-state Corn Nitrogen Rate Calculator (http://extension.agron.iastate.edu/soilfertility/nrate.aspx). Current nutrient application guidelines for corn can be found in the following publication from Drs. Carrie Laboski and John Peters with University of Wisconsin Extension: http://learningstore.uwex.edu/assets/pdfs/A2809.pdf

Nitrogen Price, Corn Price, and Sidedress Cost Inputs

Corn and nitrogen prices and sidedressing costs will have a direct impact on the profitability of split nitrogen applications. Default values for price and cost are provided in the Corn Split N tool, but these should be adjusted based on local conditions. Any change in corn yield is best priced using your local market price. Reduction in fertilizer use would need to take into account both the type of fertilizer used and the local price of that fertilizer. The default values in this tool were appropriate for a particular time and assumed a particular type of N fertilizer. Corn Split N users are encouraged to adjust this information to make it realistic of their situation.

For simplicity, we have assumed that the cost of sidedressing N is a custom rate, or a flat rate per acre. This is appropriate since most sidedressing will be done by a custom operator such as your input supplier. The default value is appropriate for illustrative purposes, but the user is encouraged to call potential sidedress application businesses to discern their price and availability for applying post-planting N on your fields.

Equipment and Hours

The Start and End Date to apply N will change with the planting date. The start date can be any time after the planting date depending on when you are likely to have time to begin. The end date needs to be before the vegetative stage you chose. For convenience, the Corn Split N product estimates when your selected vegetative state is expected to occur. If you chose an “End Date” after this estimate this product will give you a warning that end application date is after the desired end stage. It is recommended that you do not run this product with an End Date later than the expected date to reach the desired vegetative stage.

The implement description on the right side of the Scenario input section is intended to determine the acres covered per hour. Your application company may be able to provide you with an estimate of the acres covered in an hour. You would then need to adjust the default values until the “Acres worked per hour” match their expectation.

You may also need to discern from your provider the number of hours worked per day. Equipment using GPS and light bars may be able to work longer hours than equipment without these aids. For ease, the daylight hours for the date range you plan on applying nitrogen has been supplied. By clicking on “Custom Hours” you are able to enter the number of hours you expect to be in the field each day.

If you avoid fieldwork on a particular day (e.g. Sunday) or have another job that prevents you from working every day in the field, enter the number of days in 7 that you expect to be in the field. For any number less than 7, the product will adjust the probability that you will be able to apply N to all the acres entered into the Acres box.

Scenarios

Reducing Nitrogen Loss

Some farmers use post-planting nitrogen applications to reduce nitrogen fertilizer loss. Nitrogen loss via leaching is problematic on well-drained, sandy soils, whereas poorly drained soils tend to lose nitrogen via the process of denitrification during times of soil saturation.

The Corn Split N tool can help farmers analyze the feasibility and economic outcome of reducing nitrogen loss via post-planting applications. The concept is that less total fertilizer would be applied to the corn crop because less is expected to be lost. There is no expectation that yield would be increased over supplying all of the fertilizer prior to planting – only that the quantity of fertilizer loss is reduced; and, therefore, the total quantity of fertilizer purchased is reduced. Typically, to accomplish this objective, a reduced rate or starter fertilizer rate of nitrogen would be applied in the fall or around the time of planting. A post-planting application would later be applied to the growing crop to supply all its needs. The risk of this management approach is that yields could suffer if poor weather conditions prohibit post-planting nitrogen application.

Example Situation:

You’re a farmer in Story County, IA, who planted 1500 acres of corn beginning May 1. You’re planning to apply additional nitrogen between June 4 (when you expect all planting will be completed) and June 22 (before reaching V8). You estimate that 30 fewer pounds of nitrogen fertilizer would be applied using a split application approach than if all had been applied prior to planting. However, if the fertilizer is not applied by June 22, your crop consultant said to expected a 25 bu/acre yield loss on those acres not receiving the post-planting application of nitrogen.

The Economic Analysis indicates that post-planting nitrogen application would be possible on all 1500 acres in 31 of the last 32 years, or 96% of the time. The net benefit of this approach, after accounting for additional costs of the second nitrogen application and savings from your reduced nitrogen use, would result in a net savings of $3,000 each year.

In the worst year of the last 32 years, only 1073 of the 1500 acres planted to corn received post-planting nitrogen. In this case, the money saved from unused nitrogen was outweighed by yield losses on the 427 unfertilized acres. The net economic result is that, in this one year, you would lose $34,000.

The Breakeven calculation indicates that in 31 of the last 32 years, or 96% of the time, post-planting nitrogen application would have provided economic returns at least equal to the economic costs. As long more than 1474 of the 1500 acres received the post-planting application of nitrogen, the benefit would exceed the cost.

The worst case scenario gives an upper bound on the number of acres a farmer desiring to test split N applications should commit to this management style. If a farmer is confident that the machinery will be available during the necessary time, they can conduct a relatively risk free trial of split N fertilization on the worst case scenario number of acres (1073 acres in this example).

Saving Nitrogen and Increasing Yield on Sandy Soils

Retaining nitrogen in sandy soils is often problematic. Nitrogen loss is so common that in some years, yield suffers because more nitrogen was lost prior to planting than was anticipated. Thus, there is great potential for increasing yields and reducing overall nitrogen use on sandy soils by adopting post-planting nitrogen application.

Typically, to realize both reduced nitrogen application and increased yield, a reduced rate of nitrogen would be applied in the fall or around the time of planting. A post-planting application would later be applied to the growing crop to supply all of its needs. The risk of this management approach is that yields could suffer if poor weather conditions prohibit post-planting nitrogen application.

Example Situation:

You’re a farmer in Marshall County, KS, who started planted 1500 acres of corn beginning April 30. You’re planning to apply additional nitrogen between May 29 and June 13 (before reaching V8). You estimate that 40 fewer pounds of nitrogen fertilizer would be applied using a split application approach than if all had been applied prior to planting, and a yield benefit of 5 bu/acre is anticipated. However, if the fertilizer is not applied by June 7, your crop consultant said to expect a 25 bu/acre yield loss on those acres not receiving the post-planting application of nitrogen.

The Economic Analysis indicates that post-planting nitrogen application would be possible on all 1500 acres in at least 29 the last 32 years. The net benefit of this approach, after accounting for additional costs of the second nitrogen application, yield gains, and savings from your reduced nitrogen use, would result in a net savings of $45,000 each year.

In the worst year of the last 32 years, only 1034 of the 1500 acres planted to corn received post-planting nitrogen. In this case, the yield losses on the 466 unfertilized acres outweighed the yield gains and nitrogen savings. The net economic result is that, in this one year, you would lose $12,000.

The Breakeven calculation indicates that in 31 of the last 32 years, or 96% of the time, post-planting nitrogen application would have provided economic returns at least equal to the economic costs. As long more than 1131 of the 1500 acres received the post-planting application of nitrogen, the benefit would exceed the cost.