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Hudsonville, Michigan (michiganpumpkins@sbcglobal.net)

All:
I have over the last 8 years watched my phosphorus levels go up, now to the point where it is too high. Most autumns I have dumped in fresh cow manure, bagged peat moss, and gypsum. What's the culprit that's bringing up my P?
And, how to fix, since it doesn't leach very quickly?
I have (heavily amended) clay soil in this patch...
Frank

10/6/2005 7:31:07 AM

Ontario, Canada.

The phosphorus level of the soil is considered "too high" if it interferes with the uptake of other essential elements. Zinc is usually the first element to have restricted uptake when soil P becomes high. This effect on Zn uptake is pH dependent: the higher the pH, the worse the problem becomes.

High levels of P are not toxic, I don't believe it to be a large concern except for some studies which confirm mycorrhizal fungi is significantly reduced at high soil phosphorus levels above 140ppm. The development of mycorrhizal relationships were found to be the greatest when soil phosphorus levels were at 50ppm.

Fresh manure is the source.

Buckwheat fixes P from the soil. Removing a cover crop at harvest will help lower levels.

10/6/2005 10:50:10 AM

Hudsonville, Michigan (michiganpumpkins@sbcglobal.net)

Russ:
Thanks for that info...much appreciated!
are you saying that planting buckwheat will pull out P?
And then I should NOT till it in, so as not to reintroduce the P?

Frank

10/6/2005 11:59:16 AM

Ontario, Canada.

Yes, Frank that's it. Buckwheat is generally used as a cover crop to pull P out of the soil and then plowed back in to provide P in a usable form.

It is too late to plant it right now, frost will kill it. you could plant a crop it the spring after last frost and pull it out just ahead of the vines. I can't say how much will be removed.

What is your PPM

10/6/2005 1:21:03 PM

Hudsonville, Michigan (michiganpumpkins@sbcglobal.net)

Last spring it was 187ppm.
This fall 200+ lb/per acre. Not sure yet how that translates to ppm...

10/6/2005 2:25:17 PM

Ctpumpkin@optonline.net

200 lbs per acre = 100 ppm

10/6/2005 9:42:22 PM

Picton,ON (j.vincent@xplornet.ca)

there is roughly 2 million lbs in the top six inches of soi/ acre so 200 lbs / acre is 100 ppm. This level is not excessive for growing AG's
187 ppm is high but not toxic, I wouldn't sweat it!
There are a lot of factors that can account for the differences in the soil test, including different labs, time of year the sample was taken, random variation in the patch, sampling error...etc

10/6/2005 9:49:59 PM

Omaha, NE (N41-15-42 )

Frank,

There's a paper being presented at Michigan State in November on high soil phosphorus.

http://crops.confex.com/crops/2005am/techprogram/P8281.HTM

10/7/2005 12:04:09 AM

Ontario, Canada.

Frank, With frost fast approaching this week or next you could get a crop of oats in and up in time for freeze up. I would hold off on the manure.

Decaying organic matter produces organic acids which combine with iron and aluminum ions, This coupling frees up P in the soil as free Iron can tie up P. Could An application of Irionite might also work?

There are problems & pitfalls with the organic supplements too. We have never really dealt with the over applications of of manures before. We are very effectively killing off the Beneficial fungi with kindness. Your CEC can be raised further using vermiculite or calcined clay.

10/7/2005 8:36:55 AM