[USCC] P accumulation in manured fields

Fri Sep 1 18:02:58 CDT 2006

Rufus and Frank,
I have wonder if the water extraction used on soils, even though it is
adequate for testing plant available soil P concentrations, will be adequate
for testing compost plant available P.  Water tends to take on the pH of the
materials to which it is added, so water an acid soil would be at the
approximate pH of the soil, which is adequate for determining solubility of
P under the existing soil conditions.  But compost is a soil amendment. 

If I extracted a high pH compost or manure with water but the compost was
used to amend an acid soil, wouldn't the potential availability of P from
the material be influence by the change in conditions; would the soluble
fraction of P be increased do to changes in the pH in the surrounding soil?
Therefore, would the extraction of P from compost or manure using water
underestimate the available P under such circumstances?  So, is water
extraction the best method for estimating available P or would dilute acid
extraction be more adequate to determine the "potential" available fraction
of P in a compost?

Dave Schellinger
W. A. Callegari Environmental Center     

-----Original Message-----
From: compost-bounces at composter.com [mailto:compost-bounces at composter.com]
On Behalf Of Rufus Chaney
Sent: Wednesday, August 30, 2006 12:25 PM
To: compost at composter.com
Subject: Re: [USCC] P accumulation in manured fields

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Dear Frank and USCC Folks:

You raise an important issue, and I have to report that the needed method
has not been adopted at this date.

1. It has been found in numerous studies by now that soil test P (Mehlich,
Bray, Olsen, etc.) does not correlate very well with runoff or leaching of
P. These extractants have chemicals which are supposed to dissolve P that
the roots can dissolve and absorb, and that pool of P is different from the
P which enters runoff or leaches.

2. We published several examples of the disagreement between soil-test-P
(STP) and water soluble P (WSP) and the ability of added Water Treatment
Residue to lower the WSP vs. STP in our paper in the last Composting
Conference Proceedings, and the Bio-Based Plant Nutrient Product
proceedings.

3. According to the leaders in this field of research and extension, an
extraction of soil with pure water at 1 g dry soil per 100 mL, and measuring
the free inorganic "reactive" phosphate in the millipore filtered extract,
is the best correlated measure of P in field runoff tests. We have used this
ratio (Codling, Chaney et al.) and believe it is likely to be the ratio
adopted within a few years. Agreement that a STP should not be the
extraction used to predict risk of P in soil or manure is quite wide among
researchers. Papers about the water extraction will be appearing for several
years, and some official method may be selected soon. 

4. One example is reported in the paper: Kleinman, P.J.A., A.N. Sharpley,
A.M. Wolf, D.B. Beegle and P.A. Moore, Jr. 2002. Measuring water-extractable
phosphorus in manure as an indicator of phosphorus in runoff. Soil Sci. Soc.
Am. J. 66:2009-2015. This specific method is pretty much what is being
considered by experts on phosphate runoff.

Regards,

Rufus Chaney
Beltsville, MD
----------------------------------------------------------------------------
---------
>>> 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
>
>
>-----------------------------------------------------------------------
>Jerry d'Aquin, Con-Sul, Inc.   
>     One area which is of concern to me on a multi-decade time horizon is
the practice of applying alum to fields receiving high doses of poultry
litter. This approach has been promoted by the U of Arkansas as a means to
convert soluble P in litter to an insoluble form. This permits high-volume
litter applications while limiting P runoff and percolation into surface
and ground waters. In my mind, we are (at best) over-accumulating ground P
until the point when it again becomes an issue (if it ever ceased being so)
AND artificially injecting Al as aluminum phosphate into a long  term
equation -- rather than simply "biting the bullet" and  dispersing litter
over a larger area and at doses appropriate for requisite  nutrient uptake
of those crops. Am I wrong regarding the use of alum?

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