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| the attached graphics may be of interest.
the first illustrates the important role of soil N (principally SOM-N) vs. fertilizer N and the N tie-up effects of corn residue.
the second shows the poor relationship between EONR (economic optimum N rate) and OY (optimum yield). Each data point represents the EONR and OY for a particular N rate experiment.
For many experiments the EONR was less than 150 lbs of N/ac and produced an OY of more than 175 bu/ac (especially in IA).
For some experiments the EONR was less than 100 lbs of N/ac and produced an OY of more than 200 bu/ac.
Check out the bulletin at the following link for more info about these experiments
http://www.agronext.iastate.edu/soilfertility/info/nrecNCEISFC-04.p...
Bottom line is that soils with high yield potential can supply a lot of N from soil organic matter (often more than 100 lbs of N/a), especially during years with plenty of heat and moisture.
Predicting how much N will be (or has been) supplied by the soil is an on-going challenge... soil and crop sensors are showing some potential.
Are any of you using the Green Seeker or other sensor systems? how about aerial photography?
Joel
WIU Agriculture
Edited by jbgruver 8/17/2010 20:34
 (NfromSOMslide.jpg)
 (OptimalNratedataIAIL.jpg)
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 NfromSOMslide.jpg (40KB - 52 downloads)
OptimalNratedataIAIL.jpg (58KB - 56 downloads)
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Corn and Nitrogen useage
