[USCC] P accumulation in manured fields

[Rufus Chaney]

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
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>>> 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
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(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.
>  
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>(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
>
>
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>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?