[USCC] Soil test levels for nitrogen in compost

[frank]

Steve,
Great question. The goal is to provide a steady supply of nutrients 
during the growing season. When using compost we have the available 
forms and the to-be available forms. Then the many site specific 
considerations like soils that leach and soils that don't. plants that 
need  a lot of available N and plants that need a long term slow supply. 
Please see below:

Steve Diver wrote:

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>I'm looking for interpretive guides to understanding
>ammonium-nitrogen in comparison to nitrate-nitrogen on
>lab tests for soils and composts.  
>
>  
>
When deciding if the soil should have high ammonia or high nitrate I 
look at a few factors. Both are available but most plants seem to like 
nitrate better. So when growing lettuce and other leafy green I suggest 
the quick response nitrate with a continuous supply. When talking about 
trees, shrubs and places where the compost nitrogen must last a long 
time I look more toward ammonia and the slow conversion to nitrates 
without the potential loss of nitrogen due to leaching. (nitrate leaches).
Then if you have a high pH you will not want to add a high amount of 
ammonia and high nitrates can 'burn' roots especially in low pH soils.

>For example, what are the normal ranges for L, M, H, VH. 
>  
>
Soil range for agronomic rates. (available maintained in soil )
NH4-N from 50 to 150 lb per acre
NO3-N 25 to 50 lb/acre
These numbers differ a lot depending on crop type, type of irrigation, 
how fertilizer is applied, soil type,  compost

Compost
Average values for compost is:
1.61% dry wt total nitrogen
303 mg/kg Nitrate nitrogen
879 mg/kg ammonia nitrogen

In the past I wanted to group all the constituents into L, M, H VH 
ranges and make a classification system.  I got no interest  and it is 
more 'extra' work than I want to do now. But if you have the time and 
want to do that I could send you the info you will need.

Frank


>Interpretive numbers on NO3-N is easy to find, but 
>guidelines on NH4-N seems to be scarce.
>
>And then how do you interpret the numbers in relation to
>soil/compost activity when one is 2x-4x higher than the
>other.  
>
>It appears that NH4-N is normally performed for
>manure analysis as part of a nutrient management 
>plan.
>
>  
>
I think this is because during active composting and all manures there 
is a huge oxygen demand. Nitrates (NO3) do not form because there is no 
oxygen available for it to form. As the compost stabilizes and the 
Biological Available Carbon is reduced, and there is air going through 
the pile, oxygen becomes more plentiful and the NO3 can form. I think 
this is good that it doesn't form until the end (curing) because 
bacteria use ammonia as an available source and not NO3(?).  So if the 
pile dries out too soon or there is too much aeration during the 
composting process and nitrates form there may be a short supply of N 
for the microbes even though there is plenty N in the pile.






>Much appreciated,
>Steve Diver 
>
>
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-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com