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ECIN
Senior Advisor

N-- Crediting For Cover Crop

Got this off the Chat 'N' Chrew Cafe - Been more covers go in this fall around here - and have read also about other areas doing the same -- This came out of the U. Of Minnesota -- The U. Of Minnesota ? heck I didn't know they had a Ag. Department up there - Maybe Ice fishing school - But Ag ? Anyway -- What do you guys think ?

 

Ken

 

 

Nitrogen Crediting for fields with Cover Crops

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By Daniel Kaiser
Fabian Fernandez
John Lamb
Carl Rosen

University of Minnesota Extension Nutrient Management Specialists

The increase number of acres planted to cover crops has raised questions on nitrogen (N) crediting for the 2014 cropping year.  While there are many benefits touted for the use of cover crops, there are a lot of unknowns when determining N credits.  This is especially true for mixes with multiple plant species. 

One of the benefits of cover crops is scavenging of N during the growing season.  This N can potentially be released for the following year's crop.  While there may be a benefit from additional N available to the next year's crop, the process of mineralization of N through the decomposition of residue can progress over the growing season.  Thus, N may not be available during periods of rapid N uptake by corn.  This delay in availability makes it difficult to predict the amount of available N using the total amount of N per acre contained in the crop.  For small grain crops, if the crop was terminated when the crop was drying down, then no N credit should be used.

When estimating the amount of N potentially available, from a cover crop, it is important to consider the capacity of the cover crop to scavenge N.  In cases where a non-legume cover crop was planted and no N was applied, there is no reason to believe that a significant amount of N should be credited for the next crop.  If a significant amount of fertilizer N or mineralized soil organic N was left over by the 2013 crop, some N would be available for the cover crop. However, it is difficult to determine just how much of the N would be available for the next crop given the fact that not all N scavenge by the cover crop may be available in time for next season's crop.  A small credit of 10-20 lbs of N may be warranted but fields should be monitored the following year starting in June to ensure adequate N is available for the following crop.    One tool that can be used stating in June is the supplemental N decision guide for corn.  The greatest potential for N scavenging would occur where fertilizer was applied to the 2013 corn crop.

Legumes would provide the best chance of an N credit for the next year's crop.  Data are available for the use of legumes as green manure crops.  [Data from Wisconsin (see link below)]  Most of the N credits are for mono-cultures of green manure crops.  It is less clear as to how much N, if any, should be credited back when grown in a mixture and it would not be suggested to take a full credit for a legume crop in these situations.  Care should be taken not to over credit legumes the following year since deficiencies may not show up until it is too late to make supplemental applications of fertilizer N late in the season.

Wisconsin data on N credits following green manure crops
http://ipcm.wisc.edu/blog/2012/08/considerations-for-cover-crops-in-2012/table-green-manure-nitrogen...

For fallowed ground there can be a significant N credit for the following year.  One option to more accurately determine the amount of N available would be to take a two-foot depth soil sample to determine the amount of nitrate potentially available the next year.  The samples can be collected in the fall in western Minnesota and in the spring in central Minnesota, as long as no fall N is applied.  The two foot N test is less reliable for southeastern Minnesota.  For southeast Minnesota, the pre-plant N test can be taken to better determine the amount of available N.  This would provide a better estimation of available N than just taking a standard N credit.  These tests would not provide an accurate picture of the amount of available N released from a cover crop, thus they are not recommended where cover crops were present.

There is a lot of information available on the web about crediting cover crops.  Make sure that any information used is from credible sources.  While many benefits for the use of cover crops have been stated there still are many issues that have yet to be resolved, such as N crediting or other fertility concerns such as fallow syndrome in corn.  Be aware of these issues and always try to make an informed decision.  

More information for using the soil nitrate test in MN can be found at:
http://www1.extension.umn.edu/agriculture/nutrient-management/nitrogen/docs/FO-7310-B-1.pdf

The Supplement Nitrogen Worksheet for corn can be found at:
http://www1.extension.umn.edu/agriculture/nutrient-management/nitrogen/docs/NitrogenWorksheet.pdf

More information can be found on our website
http://z.umn.edu/nutrientmgmt

Visit U of M Nutrient Management on Facebook
http://z.umn.edu/fbnutrientmgmt

 

 

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7 Replies
Shaggy98
Senior Advisor

Re: N-- Crediting For Cover Crop

Next year will be year number 2 for me if I decide to try a few cover crops. This year the cover crop itself wasn't successful, but I'm not sure if the final results were a complete loss, 12" of rain in a 4 week period makes management a little off the norm. When I no-tilled wheat into these acres 6 weeks ago, they were so mellow compared to the rest of my acres it was almost like driving across a sponge. I should get my soil analysis results back shortly, so I'll see how those compare to the rest of my acres.

Our wildcard is moisture. If the cover crop taps into our subsoil moisture, it very well could be robbing Peter to pay Paul. I've only tried spring seeded cover crops followed by wheat, I'm also considering some early fall seeded cover crops that will winter kill and be followed by milo the following spring. I'll keep you all posted.

Another thing to consider when planning a cover crop strategy is residual control chemical use. Really need to read and study the label and know what your cropping plans are before you apply them.
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buckfarmer
Senior Contributor

Re: N-- Crediting For Cover Crop

I'll pretty much agree with the info. I never credit any nitogen for cover crops. One neighbor who is big into no-till and cover crops had terrible looking corn this year. Looked like he may have over estimated what the cover crop would provide.
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Shaggy98
Senior Advisor

Re: N-- Crediting For Cover Crop

My intentions for the cover crops are more for soil building and erosion control.  We need plan our CC carefully, if we use to much of our subsoil moisture we are defeating the purpose in my opinion.

 

I'll continue to try a few different strategies in front of and behind different cash crops until I find a system that I feel is right for me and my crop rotations.  If we continue to do the same thing year after year, why should we expect anything different as a result.

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ECIN
Senior Advisor

Re: N-- Crediting For Cover Crop

I'm still out to lunch on this cover crop deal - i think it has it's place or places - but on my ground - just can't get a grip on it helping me for the 20 or 30 bucks an acre it costs - Heres a quote from the artical : .  Thus, N may not be available during periods of rapid N uptake by corn.  To me - this is the same  deal with soybean credits - To me -  Years ago they came out with this credit - like 1 pound of N per bu. up to like 20 units or so then they said if you made 60 bpa then  there was 60 uints of N - now there back down to 20 units max -- no matter what the yield .  I don't figure any credits for anything other than the true N I put on and my yields have gone up by doing this .

 

The benefit of the cover would come from the organic matter - but that takes many years to come in to play - many !

 

 

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buckfarmer
Senior Contributor

Re: N-- Crediting For Cover Crop

My ground is all highly erodible. I have one landlord that gave me a break on a long term lease if I agreed to plant a cover every year. If I don't plant the cover I pay a "penalty". It's about the cost of seed and equal to the break he gave me on rent. Waiting to see if that farm performs better in the long run.
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Shaggy98
Senior Advisor

Re: N-- Crediting For Cover Crop

I've been told it takes a few years before we truly see the benefits of CC. Not sure I buy that, I planted some last spring that I thought were a complete failure due to a late freeze but it turns out that they very well could have kept the soil loose and mellow. Didn't really have a good comparison, so I believe I will try them again next spring. Haven't completely ruled out a fall seeded blend either, just not sure where to try them. Having an early summer and also an early fall harvest lets me get CC planted twice a year without any interruption of a cash crop.
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tree fmr
Advisor

Re: N-- Crediting For Cover Crop

We have acres that have been 20+ years no till and more recently bought acres that are just starting no till on.  Hoping the CC adds organic matter faster than just cash crops, which it should.  I did ask whats the NR 1 benefit to the soil with long term no till acres to my brother.  He said ya know, I don't have to use as much fertilizer as I use too and getting better yields.

So the hope is the cover crops work faster at achieving this.  Time will tell.

 

Also keep a few acres of rye as a cash crop each year, 2 reasons.  Raise our own seed and have a place to haul manure in the summer months.  Works quite well.  Not counting crop ensurance this might be our highest net profit acres this year!

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