"Raymond R. Weil" wrote:
>
> Dear Saneters,
>
> About phosphorus water pollution from agricultural land: yes this is a serious
> problem where soil reserves of P have been built up, especially where organic
> fertility sources as animal manure and compost have been used. The main pathways
> of P loss to waterways are through (1) P bound sediment (and later released from
> the lake or river bottom) and (2) P DISSOLVED in the surface runoff water.
>
(clipped)
>
> The problem comes occurs when the animal producers, be she or he a family farmer
> or a large corporation, import feed and/or fertilizer--whether organic or
> synthetic--that more than makes up for the nutrients exported in the crops and
> animal products. Relying mainly on animal manure (composted or raw) for a source
> of Nitrogen (as do most dairy farmers and many organic farmers) will usually
> result in a build up of excessive Phosphorus because the ratio of N to P in the
> fresh animal manure (and even more so in the compost from which some N has been
> lost) is lower by almost an order of magnitude than the ratio in the crop plants
> being grown. In the case of swine and poultry manure this situation is often
> aggravated by excessive animal feed supplementation with P as calcium phosphates
> to make up for the fact that non-ruminants cannot digest most of the P in grain
> (the phytin form). Hence the new push for low phytic acid grain varieties as a
> band-aid measure to help the nutrient balance in our unbalanced animal
> agriculture.
>
> I hope this helps to explain why P has become a pollution problem despite the
> great (but variable and finite) ability of most soils to bind it tightly.
>
> --Ray Weil
>
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