[NAFEX] leachy phosphorous

Road's End Farm organic87 at frontiernet.net
Thu Jun 25 16:04:20 EDT 2009


On Jun 25, 2009, at 3:32 PM, Mark Angermayer wrote:

> Rivka wrote:
>  
> "c) during just about all of the evolutionary history of these plants 
> humans were not applying P annually to supply them:
> therefore, it's got to be made available by some process not involving 
> human intervention."
>  
> That may be true, but evolution typically produces very low 
> yields with the exclusive goal of survival of individual species.  The 
> yields nowadays of many crops remove far more P than can be supplied 
> without the aid of human intervention. 
>  
> Mark
> KS

That's a very good point (though I'm not sure whether total biomass 
production of modern crops is different, or only production of the 
portion considered edible by humans). To amplify it, most of the yields 
in natural systems stay in the immediate area (though animals and wind 
do move some of them), while most of the yields in modern farming are 
removed from the site and sold long distances away. In any case in 
which the amount repeatedly removed from the field is more than it can 
renew for itself each year, amendments will eventually need to be 
brought in to replenish this amount (though nitrogen can be replaced in 
some cases by cover crops).

However, my main point was that P can't simply always become 
unavailable, with no natural mechanism to make it available again to 
plants. Whether that mechanism is sufficient, or even functional, in a 
specific farm situation is another question. But if we understood the 
natural function, we might be able to figure out how to better take 
advantage of it. -- I don't know whether it is understood, but hasn't 
been explained in this discussion; or whether this is one of the areas 
that modern soil science is still working on.



--Rivka
Finger Lakes NY; zone 5 mostly
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