1. Demonstration of In-Season Nitrogen Management Strategies for Corn Production John Sawyer John Lundvall Jennifer Hawkins Department of Agronomy Iowa State University

2. 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.

3. 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 ApplicationN Application Treatment Treatment Identifier lb N/acre 0 - - - - - Control0 60 - - - - - Pre reduced N rate60 Rate determined in-season Pre reduced + in-season N rate 60+ 120 - - - - - Pre agronomic N rate120 Rate determined in-season Pre agronomic + in-season N rate 120+ 240 - - - - - Pre well-fertilized reference N rate 240

4. In-Season N Management Project Why 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

5. In-Season N Management Project Why 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

6. In-Season N Management Project  Why a zero N rate?  Document N response and indication of soil system N supply  Why a high non-limiting N rate reference?  Document maximum N response in corn “coloration” and yield

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

9. J. Hawkins and J. E. Sawyer, 1999-2005 N Rate Calibration

10. J.E. Sawyer – Five C-S Sites in 2003 Sensing Timing Comparison

11. Relative SPAD Chlorophyll Meter Value and In-Season N Rate to Apply Relative CM Value*N Rate to Apply** RCMlb N/acre < 0.88100 0.88 – 0.9280 0.92 – 0.9560 0.95 – 0.9730 > 0.970 * Readings taken from approx. V15 to VT corn growth stage. ** Suggested N rates limited to a maximum of 100 lb N/acre.

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

13. Yield Summary for 22 Sites, 2004-2005

14. Sites Needing Additional N and Where In-Season N Applied In-Season N Management Strategies Project 20042005 N RateSitesYieldSitesYield lb N/acren ( )*bu/acren ( )*bu/acre 60184162 60+7 (4)1968 (4)176 240217186 120214204 120+2 (2)2251 (0)208 240218215 * ( ) Sites with significant yield increase to in-season N.

15. Economic Summary, 2004-2005

16. 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 increase  Continuing Questions  Improving response to in-season N n Early N stress detection (V10)? n 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