This document discusses a study examining the effects of historical nitrogen application rates on current corn yield and nitrogen use efficiency when fertilizing at the optimum rate. The study found that after 15 years, fields that previously received higher nitrogen rates produced higher yields and had greater nitrogen use efficiency compared to fields that received lower historical nitrogen rates, even when all fields were fertilized at the optimum rate. The document suggests this may be due to the higher levels of soil organic carbon in the fields that received higher historical nitrogen application.

1. Is Soil Organic Matter
Important for Corn Yield?
Integrating Soil Carbon Stabilization
Concepts and the Nitrogen Cycle
Hanna Poffenbarger (PhD student)
Mike Castellano, Dan Olk, John Sawyer, Johan Six

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15' 40' Border
40' Alley
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8. After 15 years, how does historical N rate affect yield
and N use efficiency when fertilized at the optimum rate?

9. After 15 years, how does historical N rate affect yield
and N use efficiency when fertilized at the optimum rate?
Historical Nitrogen Rate
and Extant Soil Organic Carbon
Yieldwhenfertilized
attheoptimumrate

10. After 15 years, how does historical N rate affect yield
and N use efficiency when fertilized at the optimum rate?
Historical Nitrogen Rate
and Extant Soil Organic Carbon
Yieldwhenfertilized
attheoptimumrate

11. Nitrogen Retention, Saturation
& the Carbon Saturation Concept

12. Linking C Saturation & N Dynamics
0%
100%
Maximum Capacity
(Saturation)
Carbon Inputs at Steady State
POM C/N Ratio
N inputs
transferred
to SOM
Net
Nitrification
RelativeUnits
0%

13. After 15 years, how does historical N rate affect yield
and N use efficiency when fertilized at the optimum rate?

17. Central Iowa
AONR = 202 kg N ha-1
~70 kg N ha-1 unrecovered
South Iowa
AONR > 269 kg N ha-1
~180 kg N ha-1 unrecovered