Nitrogen Use Efficiency

Charles Shapiro, Extension Agronomist shared a recent column of his that I found it to be very interesting, so I thought I’d share it? Do you know your nitrogen use efficiency? (NUE).

His column follows: “Do you know your PFP? What the heck is PFP? In science speak, PFP is an abbreviation for Partial Factor Productivity. It is one way to calculate nitrogen use efficiency, which is sometimes abbreviated NUE. That probably does not help much either. What it means, related to corn production and nitrogen use, is how much corn is produced with a pound of nitrogen fertilizer.

One can think of it as the miles-per-gallon type number for nitrogen efficiency in corn production. A car’s miles per gallon do not tell the whole story.

A small hybrid might have 50 miles per gallon compared to a pickup, but if the pickup is pulling a large load, the small hybrid might not be able to accomplish the task, or need to make several trips to get the job done, canceling out the advantage. But when all things are equal, miles per gallon will give some idea of gas efficiency.

WITH NITROGEN AND corn, the pounds of corn grain produced per pound of nitrogen applied is not the whole story since the plant takes up nitrogen from other sources. Another measure of efficiency would be the pounds of grain relative to all nitrogen applied and accounted for as credits. For years, University of Nebraska-Lincoln recommendation procedures have been based on credits from other sources such as irrigation water, manure, soil nitrates and legumes. Using these credits will increase the PFP of fertilizer nitrogen compared to ignoring them.

My farm management professor from college used to say, “You can’t manage what you don’t mea- sure,” so as we work toward increasing our nitrogen use efficiency we need to have a measurement that will help us know if our changes in management are producing benefits. One of these measures could be PFP.

SOME NUMBERS MIGHT help. One way to calculate the PFP is to take the corn yield, multiply by 56 and divide by the pounds of nitrogen applied. Here are two examples, both with yields of 200 bushels per acre. First, 150 pounds of nitrogen were applied to the field; this calculates to a PFP of 75 [(200 x 56)/150]. Second, 225 pounds of nitrogen were applied to the field; this calculates to a PFP of 50.

To put this in perspective, in Nebraska when the nitrogen purchased is divided by the reported corn yield, the pounds of grain per unit of nitrogen comes out to a PFP of over 60. This number has been increasing since the 1960s. The higher the better. Hypothetically, if one were to apply only the nitrogen that was removed in a bushel of corn (0.7 pounds nitrogen), the PFP would be 80.
This is not realistic since nitrogen is needed to grow the rest of the plant, and we use 1.2 pounds as a rule of thumb for the amount of nitrogen to grow a plant with one bushel of corn with 0.7 pounds nitro- gen in it.

SO HOW CAN we improve our PFP? That is where taking credits for already available nitrogen comes in. If these credits are taken, and we reduce our applied nitrogen, we increase our PFP. In the ex- ample above, where the PFP was compared for the two nitrogen rates used to produce 200 bushels of corn, the 150-pound nitrogen rate was derived from the UNL Corn Nitrogen Calculator with credits for soil organic matter, soybeans as a previous crop and some irrigation nitrates. The 225-pound nitrogen rate was derived from giving a general 50-pound credit for soil nitrogen.
Use your calculated PFP to help you decide if you need to look for more ways to credit the nitrogen that is there. If the issue is not nitrogen, then some other management factor is keeping your yields low, and that needs to be addressed.

IN A RECENT issue of the Journal of Environmental Quality, UNL professor Richard Ferguson documented the situation in the Central Platte Natural Resources District.

There he found that although there was high PFP when fertilizer nitrogen was calculated, when the potential credits were included in total nitrogen available, the PFP went down from the 60s to the 40s. This indicates there may be nitrogen credits that could be used.

Efficiency has to be balanced with total production. Nitrogen use efficiency is highest before maxi- mum profit and yield are achieved, so one can’t use PFP to determine nitrogen recommendations. How- ever, in order to produce corn profitably with low corn prices, efficiency has to be high.

Calculate the PFP on various fields, and if they are below 65, then take the time to determine if there are missing credits available.

Go to http://cropwatch.unl.edu/soils to find many tools and resources to improve nitrogen use efficiency.”

While at CropWatch, please also take time to complete our CropWatch survey by this Friday, December 19 at: https://www.surveymonkey.com/s/CropWatch. If you would like a chance to win a free Crop Production Clinic registration or 5 weed guides, please include your contact information in the optional last question. Otherwise, your survey will remain anonymous. We would really appreciate your feedback and suggestions.

Field Assessment Meetings
The past week I along with several other Extension Educators and Charles have been involved in a series of Field to Market field assessment meetings to improve efficiency in farming practices and production. We had sessions in Clay Center, Geneva, Auburn, Fairbury, Aurora and Fremont with 27 producers participating. The goal of the effort is to quantify several indicators to increase understanding of the environmental and economic impact of management practices and to determine which practices will improve sustainability without decreasing economic value. We also want to communicate to the general farming community and the public the efficiencies that exist in agriculture and future goals to continue to make improvements.

We’re working with the Field to Market team and the website: http://www.fieldtomarket.org. Producers that participate will input their production practices on individual fields for 2013 and/or 2014 and have that information summarized. The information is confidential, but eventually they’ll be able to compare their fields to others in the Nebraska project. I know that both the Soybean Growers and Corn Growers are encouraging their producers to participate.

I did not host a session last week, but hope too after the 1st of the year. There is no charge to participate, so if you’d like more information or are interested, give me a call 402-362-5508 or email me at gzoubek1@unl.edu.

Farm Bill Education Meeting
We had about 320 people attend our Farm Bill Educational meeting last Tuesday Dec. 9th and I heard several positive comments about the presentations. It’s an extremely complicated program and producers are encouraged to attend more than one session as well as check out our webpage that includes some excellent tools to help you determine the best options for your farm situation.

For more Farm Bill information, go to: http://agecon.unl.edu/farmbill.

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About extensionupdate

I'm a UNL Extension Educator located in York Nebrasksa. I work primarily in the area of irrigated cropping systems. Water and nitrogen management are areas of importance so that we maintain water quality and quantity.
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