Nitrogen - Microbes Vs. Plants needs #118457 - Ask Extension


Nitrogen - Microbes Vs. Plants needs #118457

Asked March 22, 2013, 6:45 PM EDT

When using "woody-organics" as amendments, and If eventually, the nitrogen becomes available again, but there can be a year or two of nitrogen deficiency, my questions is: If I have the patience's, and "continuously" add new top-dressing of oak leaves, and various manures in small amounts, then would I not at some point in"time", eventually start getting a release of Nitrogen throughout the year that would supplement the microbes in the soil, and also feed the roots of the plants? Basically, the system would find a balance? Respectfully, weather being an influence on the cycles.

Volusia County Florida

Expert Response

Thanks for your question. So my answer is going to be a "yes", but it might take a really long time (10-15 years) and depending on your soil in Florida, very difficult to reach levels that are sufficient for a crop during the growing season. If you are not adding any "quick" release forms of organic nitrogen, then the amount of nitrogen made available from the eventual decomposition of the high C:N ration materials (brown, woody) might just be taken up again by the microbes to break down the new additions of woody materials. Think of woody additions primary as a soil amendment, not a fertilizer. If you want to feed plants in the current growing season then you will need to apply nitrogen in a form that can be readily available while you are building up the soil organic matter. At some point, yes, you should be able to build up the soil organic matter to levels where you don't have to apply organic materials each year, maybe not even a quick release form during the season. But, I see that you are from Florida. Those sandy soils, unless on a high organic matter muck soil, lack much ability to build up organic matter levels. In my opinion, I would try to build up the soil as much as possible with organic materials if only to increase its ability to retain nutrients and hold water, something that most native Florida soils don't do very well. I would then find a source of organic nitrogen that is quick releasing and a good fertilizer, which usually means that its nitrogen content is above 3-5%, think composted chicken manure, or concentrated forms like seed meals or blood meals. Don't rule out the use of cover crops either. I think you will likely need an "all in" approach, a combination of composts, mulches, cover crops for biomass and nitrogen fixing, and high nitrogen organic fertilizers. 
John McQueen Replied March 25, 2013, 11:46 AM EDT
Thank you; well written, I understand. I have test Planted vetch @ clover; started growing winter rye to build tilth
Question: Arbuscular Fungi that have the Ectomychorizzal partnership: they aren't fans of Nitrogen(?) Am I going to trade off soil life diversity by inputting N ?
The Question Asker Replied March 25, 2013, 12:38 PM EDT
I am not aware of AM Fungi not being fans of nitrogen, as I understand it, the plants aren't very likely to associated with them if there is adequate phosphorous present. You might read this article - On-farm Production and Utilization of AM Fungus Inoculum ( to get some ideas about how to use AM fungi and how to produce it on your farm as a soil inoculant. I don't think you are trading nitrogen for soil life. If you are applying organic nitrogen I think the microbes will be quite happy since they will be the ones to help mineralize it. I want to stress that it should be used in limited amounts and only when others ways of supplying N aren't enough. If you are certified organic, please check with your certifying agent before you make any changes that might effect your Organic System Plan. This article summarizes all the main ways to supply nutrients on certified organic farms and it worth checking out - 
John McQueen Replied March 25, 2013, 1:05 PM EDT

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