Regional Nitrogen Rate Guidelines John Sawyer Department of Agronomy Iowa State University

Regional Effort - Participating States and University Personnel: John Sawyer, Iowa State University Emerson Nafziger, University of Illinois Gyles Randall, University of Minnesota George Rehm, University of Minnesota Larry Bundy, University of Wisconsin Brad Joern, Purdue, University Robert Hoeft, University of Illinois Carrie Laboski, University of Wisconsin Robert Mullen, The Ohio State University Randy Killorn, Iowa State University Sylvie Brouder, Purdue University

Exploring a Regional Approach to N Rate Guidelines  Diverse N rate recommendation systems across states  Lack of optimum N rate relationship with corn yield  Concerns about N rates with corn yields at record levels  Historically high N fertilizer prices

Historic Nitrogen:Corn Price Ratios

Corn Yields and N Rates

Methods for Analyzing N Response Data 43 Corn Following Soybean Sites in Iowa ($0.22/lb N:$2.20/bu) 43 Sites35 Responsive Sites MethodN Rate Net Return N Rate Net Return lb N/acre$/acrelb N/acre$/acre Mean of EONRs EONR - Mean Yield Maximum RTN Discrete Mar. Prod Site Optimum Measured Yield † Yield History † † 1.2 lb N/bu factor, 50 lb soybean rotation “credit”

Maximum Return To N (MRTN) Database Driven Approach  Previously described by Nafziger, Sawyer, and Hoeft (2004); and Sawyer and Nafziger (2005)  Accumulate corn N response data from many recent trials  Determine economic response and most profitable N rates directly from trials in N response database Data → N Rate Guidelines

N Response Trial Database  3 to 4 replications  5 to 7 N rates – spring and sidedress  Non-irrigated  High and very high yield potential soils  Experiment station or producer field  Corn following Soybean (SC) and Corn following Corn (CC)  Grain yield measured for each N rate  N Response curve fit to each trial

698 Trials > 95% since 1990 > 60% since 2000

Calculation of MRTN  1 st - Compile database from corn yield N response trials for desired rotation

Calculation of MRTN  2 nd – For each trial in database calculate Return To N (RTN) using the a, b, c and plateau values from each response curve  For every 1 lb N/acre from 0 through 240 lb N/acre calculate the yield increase over the yield obtained with zero lb N/acre  RTN = yield increase times price of corn minus the cost of N

Calculation of MRTN

 3 rd - Find the N rate with the greatest average return to N, this is the MRTN and N rate at the MRTN

Calculation of MRTN  4 th - Find the N rates with returns to N within $1.00/acre of MRTN  This provides a range of most profitable N rates LOWHIGH

Can Examine Different Fertilizer N and Corn Prices  Corn held at $2.20/bu  Fertilizer N prices at $0.11, $0.22, $0.33, and $0.44/lb N  Gives N price:corn price ratios of 0.05, 0.10, 0.15, and 0.20

Effect of Price Ratio on Net Return HIGH MRTN LOW $2.20/bu $0.11/lb N $0.22 $0.33 $0.44

Effect of Price Ratio on Net Return

Example N Rate Guidelines Based On MRTN Approach - Iowa Previous Crop Price Ratio SoybeanCorn LOW † MRTNHIGH † LOW † MRTNHIGH † $/lb:$/bu lb N/acre † LOW and HIGH rates approximate the most profitable range for $1.00/acre below and above the MRTN for each price ratio.

Effect of Price Ratio on Expected Corn Yield

Iowa SC Dataset, 0.10 Price Ratio

Advantages of MRTN Approach  Can use a variety of N response trials  Uses yield response rather than yield  Specific responses of each site considered  Easy to add new trial data  Not excessively influenced by non- responsive sites  Straightforward calculations and uses economic outcome  Can create dataset sub-groups  Can evaluate risk assessment  Can include environmental costs

Corn Nitrogen Rate Calculator Resources for Regional Approach  Regional publication  Web based MRTN calculation tool Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn

Economic Return at N Rates Above and Below Each Site Optimum