permaculture

["Lawrence F. London, Jr." <venaurafarm@bellsouth.net>]

-------- Original Message --------
Subject: Re: [SANET-MG] Soil solution concentrations of phosphorus
Date: Wed, 29 Dec 2010 10:47:39 -0500
From: James Kotcon <jkotcon@WVU.EDU>
To: SANET-MG@LISTS.IFAS.UFL.EDU

Perhaps this discussion illustrates the problems that growers have in 
understanding soil test reports.  While the soil solution concentration 
of phosphate may be 1 ppm, the "available" (extractable) phosphate 
levels are much higher, and soil test recommendations often aim for the 
450 ppm "available" phosphate as a basis for fertilizer recommendations. 
 The complexity is hard enough for experts to grasp, and a clearer 
description in soil test reports would help many of our growers.  It is 
surprising how many growers attend our workshops on "How To read Your 
Soil Test Report" each year.

In our soils, we often run into problems with phosphate fixation 
(precipitation as insoluble iron or aluminum phosphates) especially at 
acid pH levels.  Adding lime increased the "available" phosphate in our 
soil even without adding compost or other amendments.  It is not 
necessarily a microbial function, just "simple" solution chemistry.

Jim Kotcon