Demonstration of In-SeasonNitrogen Management Strategies

for Corn Production

John SawyerJohn LundvallJennifer HawkinsDepartment of AgronomyIowa State University

In-Season N Management Project Objectives

Demonstrate use of corn plant N deficiency - sufficiency monitoring to determine need and rate of in-season N application and effect on corn yield.

Compare effect of set preplant or early-sidedress N rates (Pre N) on corn plant N sufficiency and N stress development, frequency and rate of needed in-season N application, total N applied, corn yield response, and economic return.

In-Season N Management Project Nitrogen Application In Field Strips

* Corn-soybean rotation N rate. Pre N refers to N applied preplant or early sidedress.

Pre N Rate* In-season N Application N Application Treatment Treatment

Identifier

lb N/acre

0 - - - - - Control 0

60 - - - - - Pre reduced N rate 60

60 Rate determined in-season Pre reduced + in-season N rate 60+

120 - - - - - Pre agronomic N rate 120

120 Rate determined in-season Pre agronomic + in-season N rate 120+

240 - - - - - Pre well-fertilized reference N rate 240

In-Season N Management ProjectWhy Two Pre N Rates?

Apply an agronomic Pre N rate 120 lb N/acre at mid-point of current ISU

recommended N rate range for S-C rotation Assumes Pre N rate sufficient most years, but

offers rescue system if N deficiency develops during early vegetative growth (high N loss or greater N need)

Does not allow N rate adjustment if less than agronomic rate would suffice in a particular year

In-Season N Management ProjectWhy Two Pre N Rates?

Apply a reduced Pre N rate Assumes more N will need to be applied in-

season most years Allows for potential closer match between

corn N need and application each year Having some Pre N applied limits severity of

N stress and potential development of irreversible yield loss

In-Season N Management Project

Why a zero N rate? Document N response and indication of soil

system N supplyWhy a high non-limiting N rate reference?

Document maximum N response in corn “coloration” and yield

Minolta SPAD Meter Readings Collected from V13 – VT Corn Growth Stages

J. Hawkins and J. E. Sawyer, 1999-2005

Relative R1 Stage Ear Leaf Chlorophyll Meter Reading vs. Applied N Rate Difference from Economic N Response

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

-240 -200 -160 -120 -80 -40 0 40 80 120 160 200 240Difference from Economic N Rate, lb N/acre

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1999-2005Regression FitUCLLCL

RCMR = 0.97 + 0.000614*ND - 0.000004897*ND^2 RCMR = 0.99 for ND > 63 R2 = 0.73***

N Rate Calibration

J.E. Sawyer – Five C-S Sites in 2003

Relative Leaf Chlorophyll Meter Reading vs. Applied N Rate Difference from Economic N Response

0.50

0.60

0.70

0.80

0.90

1.00

-200 -160 -120 -80 -40 0 40 80 120 160 200Difference in Average N Rate, lb N/acre

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C-S_V8

C-S_V15

C-S_R1

C-S_R3

Sensing Timing Comparison

Relative SPAD Chlorophyll MeterValue and In-Season N Rate to Apply

Relative CM Value* N Rate to Apply**

RCM lb N/acre

< 0.88 100

0.88 – 0.92 80

0.92 – 0.95 60

0.95 – 0.97 30

> 0.97 0* Readings taken from approx. V15 to VT corn growth stage.** Suggested N rates limited to a maximum of 100 lb N/acre.

In-Season N (UAN Solution) Applied from V13 to R1 Corn Growth Stages

Yield Summary for 22 Sites, 2004-2005

N Application Mean† Number of Sites with MeanTreatment Total N Applied In-season N Applied Yield

lb N/acre n bu/acre

0 0 141a‡

60 60 179b60+ 117 21 187c

120 120 196d120+ 129 6 196d240 240 200e

when followed by the same letter (p ≤ 0.10).

In-Season N Strategies Project, 2004-2005

† Sum of PRE N rate and in-season N rate, averaged across all sites.‡ Yields within a row for each site are not significantly different

Sites Needing Additional N and Where In-Season N Applied

In-Season N Management Strategies Project2004 2005

N Rate Sites Yield Sites Yieldlb N/acre n ( )* bu/

acren ( )* bu/acre

60 184 16260+ 7 (4) 196 8 (4) 176240 217 186

120 214 204120+ 2 (2) 225 1 (0) 208240 218 215

* ( ) Sites with significant yield increase to in-season N.

Economic Summary, 2004-2005

N Application N ApplicationTreatment Rate Yield Net

Comparisons† Difference Difference N Cost Income Returnlb N/acre bu/acre

60 pre vs. 60+ 57 8 24.74 18.40 (6.34)

120 pre vs. 120+ 9 0 4.88 0.00 (4.88)

60 pre vs. 120 pre 60 17 18.00 39.10 21.10

60+ vs. 120 pre 3 9 (6.74) 20.70 27.44

60+ vs. 120+ 12 9 (1.85) 20.70 22.55

‡ Calculations use a corn price of $2.30/bu, $0.30/lb N and an application charge of $8.00/acre.

Gain/Loss‡In-Season N Strategies Project, 2004-2005

- - - - - - - $/acre - - - - - - -

† Calculations compare the change in values by subtracting the first listed treatment from the second.

In-Season N Management Project Summary

Best single site response to in-season N 60+ In-season N applied at V13, rained > 2”

after application: 32 bu/acre yield increaseContinuing Questions

Improving response to in-season N Early N stress detection (V10)? Early In-season N application (ASAP)?

• Waiting to apply in-season N may be too late in Iowa conditions

• Rainfall to have In-season N in zone of active roots Improving identification when reduced Pre N

rate adequate