[USCC] Soil test levels for nitrogen in compost

[LARRY SIKORA]

One needs to have a value of the carbon content of the compost as well as
the N content to help determine the probable fertilizer value of the
product. Composts made from municipal trash may have C:N ratios that near
20 and may not provide any fertilizer N to plants the first year of
application. Composts made from biosolids and woodchip mixtures may have
little fertilizer N in the final product depending upon what size screen
was used to remove woodchips. Even manures are similarly influenced.
DaAiry manure solids that result from a screw press that separates the
solids from the liquid have greatly different fertilizer value than the
original manure. Therefore, the ingredients in the compost and any
treatment of the product such as screening and grinding will influence the
nitrogen fertilizer value of the compost.

If one could duplicate in the lab or greenhouse the conditions that the
compost will be used (mixed with soil or potting material) even for a
brief time of two weeks after which when the N or even P content of the
mixture would be determined, a more accurate evaluation of the fertilizer
value of the compost would be possible.


Larry Sikora
Compost Systems and Utilization
PO Box 6076
China Village, ME 04926
(207)968-2268
ljsikora at fairpoint.net______________________________________________________________________________
> I think it's important to remember significant figures when providing
> this kind of general information.  Without contesting the range you
> suggest, it is inaccurate to provide nitrate and ammonia in terms of
> general values down to 1 mg (or ppm if one prefers).  I think that the
> nearest 50 mg/kg is the most accurate such a discussion should suggest,
> and probably the nearest 100 mg/kg.
>
> Thus using your numbers:
>
> NO3:  300 mg/kg
> NH4:  850 or 900 mg/kg
> Total N: 16,000 mg/kg
>
> On a more specific note, Ericaceous species: blue berries, azaleas,
> rhododendrons, mountain laurel, and heather as examples, absorb most
> nitrogen in form of ammonium-nitrogen.  Grasses, flowering annuals,
> herbaceous perennials and vegetable plants absorb most nitrogen in form
> of nitrate-nitrogen.  Trees and many woody perennials tend to absorb
> both equally well.
>
> Peter Severtson
> Biosolids/Composting/Soils
> Department of Ecology
> 15 West Yakima Avenue
> Yakima, WA  98902
> (509) 575-2605