[USCC] P accumulation in manure/extraction choice

[LARRY SIKORA]

Frank, Rufus et al,

The extraction of compost samples to help gauge the amount of phosphorus
that may run off land from the application of compost and the plant
available phosphorus that would act as a plant fertilizer are two
different types of phosphorus. These types are not mutually exclusive but
sufficiently different to warrant different extraction methods. When
attempting to gauge the phosphorus portion that may run off a parcel of
land amended with compost, the water extract appears to be the extraction
choice. The phosphorus content that one is trying to measure is
essentially the P that will runoff in the first substantial rain event.
After the first rain event, the majority of the water soluble P should
have moved off the area of application if the land has runoff potential.
The agencies that permit the application of composts, biosolids, or
manures are interested in this pollution potential from amendments.

The portion of compost P that is available to plants is of interest to
agencies that oversee nutrient application to fields and monitor nutrient
management plans. This fraction is different because the P is one that
will be available to plants over nearly the entire growing season, not
just that available during the first substantial rain event. In this case
the more chemically aggressive extraction methods are used. Which
extraction method to used is debatable and until considerable research is
conducted to answer the question, it may be best to choose the recommended
extraction method that the State soil test laboratory uses in whatever
State you are applying compost. The State agency is familiar with the
values that come from the particular extraction and are comfortable making
decisions based on the extraction data. This approach may be slightly
shortsighted because the plant available phosphorus is that from a mixture
of compost (or manure) and soil from the land where the compost is
applied. Testing the mixture and the soil alone  and comparing the P
values may be the best method for determining the plant available P in the
compost using extraction techniques


Larry Sikora
Compost Systems and Utilization
PO Box 6076
China Village, ME 04926
(207)968-2268
ljsikora at fairpoint.net


>>>> frank at compostlab.com 08/29/06 12:50PM >>>
> Rufus,
>
> First I wonder what type of P test should be done on compost to measure
> the 'problem' phosphorus?
>
> I suggest 'Dissolved acid-hydrolyzable phosphorus'. But first we should
> know if when using this method adding Al to the compost will reduce the
> measured P -as we need it to do if we use Al to solve the problem.
>
> SM 4500 Method: filter a water extract (suggest 1:5 w/w) thru 45um pore
> membrane filter / add dilute acid and boil for 90 min.
>
> Frank
> ---------------------------
> (snip)
>
>>High P accumulation in soil is already regulated in some states.
>> Imperfectly regulated. Composts are not yet strongly regulated in
>> relation to plant available or water soluble P in the amended soil, but
>> regs are moving toward limiting the Water Extractable Phosphate (WEP)
>> of the soil amendment or amended soil. Slopes and other factors which
>> affect runoff and erosion are increasing included in planned
>> regulations for manure P applications.
>>
> --------------------------
>>(snip)
>>
>>Most evidence shows that the P is adsorbed on Fe and Al hydroxides,
>> although some is slowly converted to inorganic compounds of P in the
>> soil or diffuses inside the micropores in the oxides. Plants can
>> utilize the adsorbed and organic P, and even the P compounds, by the
>> mechanisms they use within the rhizosphere to dissolve and absorb soil
>> P for normal soils. We did one test of the P available to wheat from
>> soils on my long term biosolids plots at Beltsvsille and found that
>> with no P fertilizer the wheat obtained adequate P for full growth. So
>> the P adsorbed on Fe and Al has remained plant available. Other's
>> research also supports this conclusion.
> .....
>>Regards,
>>
>>Rufus Chaney
>>Beltsville, MD
>>