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| Soybeans are net users of N (i.e., harvested beans remove more N than is added to the soil by crop residues) BUT thinking about N from a maintenance perspective is not particularly useful.
N availability is so dynamic in soil and crops like corn are so sensitive to N availability that what really matters is not how soybeans (or any other crops/cover crops) deplete or enhance total N in the soil but rather how the timing of plant available N is affected.
Soybean residue contains ~ 1 lb of N per bushel of soybeans harvested but the C:N ratio of soy residue is generally > 20:1 and decomposition of soy residue normally does not result in a major increase in plant available N.
In comparison, corn residue contains ~ 0.5 lbs of N per bushel of grain but the C:N ratio is generally 60-100:1 and the decomposition of corn residue normally results in significant N tie-up.
the articles at the following links may be of interest.
https://www.certifiedcropadviser.org/files/certifications/certified/...
http://www.smallgrains.org/springwh/March09/Carbon/Carbon.html
Joel
WIU Agriculture | |
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Nitrogen from Soybeans
