Leaching Phosphorus from Soils thru Tile lines... Really?

[Admin]

Good morning Jim,



Hope your Christmas was joyful. I have read this article and I also went to a local soil health seminar last week where this very subject was discussed at length. I haven't had this issue on my radar screen at all but I am now curious about what is actually going on. I always thought that P was relatively stable in the soil and was difficult to get it into a soluble form. The way this article makes it sound is that an active microbe environment will mineralize elemental P into soluble P2O5 that the plant can use or will leach rapidly deep into the soil profile and out the tile outlet if the P2O5 is not used for plant nutrition. Assuming that theory is correct, wouldn't tissue and sap test show P2O5 off the charts since it is so soluble in the soil profile? The other theory that was discussed last week was since the Clean Air Act was enacted, we are not getting the Sulfur from the atmosphere and the pH of rain water has risen dramatically allowing P2O5 to become more soluble. Their solution was using Gypsum to bind the water soluble P2O5 to Calcium. I am not sure on that one, I need to study the chemistry of that claim further. The obvious source of P contamination would be surface applied manures or P fertilizers on frozen ground then large rain events occurring shortly after application leaching P2O5 into streams via run off. The other obvious source is dead soils that have had heavy inversion tillage destroying soil structure and are very easily carried to the streams by erosion both by water and wind. I one thing I haven't heard at any of these discussions is Glyphosate's impact on making P2O5 water soluble and easily leachable. I know at your webinar last year this was discussed but I need to review the presentations further to understand the mechanics of this theory. I know that the soil test we use measures P2O5 with Bray 2 extract and tries to predict how much P205 will be released through the season. I am thinking that the test the EPA is using must be a Water Soluble Extract test measuring water soluble P2O5. I wonder if Bob Perry could run a WSE on P2O5 on some soil to get an idea what we are dealing with. All things that make me go Hmmm.



Best Regards,



Dave

[Admin]

Dave.
Good to hear from you as always. This has and continues to be the most blessed and unique Yule Season in my lifetime. All of the family except Daniel and Christian were issued a one year exclusionary order by Canadian Immigration two days before Christmas. You see my address is now in ND. Today that features a blizzard and three rooms in a small motel which is featuring kitchen privileges at the Bistro. I'll recount the details in a mailing for the new year.
To your comments.... your understanding and mine are the same concerning the stability of P in soil or for that matter in the presence of any cation. The role of improved aerobic soil conditions and increased levels of water soluble P as measures by Bray 1, and Olsen has been a consistent observation for over 30 years using PAL testing and Cursebuster type tillage. If the P were actually leaching to any significant amount I wonder it I would be finding levels on the increase in the 0-3 and 0-6 and 3-6 profiles? If it's lost how could I be finding it. It would be interesting to compare .4 molar HCL extraction P amounts in 0-6 profile over time too. If the total P found is NOT decreasing more than crop removal would account for, then how much can P be leaching out?
Any cation will react with P in soil solution to keep it attached to the soil colloidal complex. It is very strongly attached as well. Magnesium is a powerful bond so adding Gypsum which could force more mag off the colloid into soil solution would bind with the P in solution. The compound formed will still seek a negative charge. I don't know that a solution is as simple as adding Gypsum for the reasoning above.
I think the issue we are hearing about here is real and for the reasons I have suggested vis a ve movement in a water soluble compound. Do I think this is a major cause of algae blooms and hypoxia? Absolutely not.
I think the Northern Ohio University study which implicates Roundup and no - till practices is on the right track. Just take a candid look at the soil loss taking place in lake - laid silt soils in NW OH. Now that OSU has kicked the ball on down the field in support of doing tillage the "never-till" group is flipping out. The reaction is symptomatic of a deeper issue.
I think that the combination of shallow rooted covers and main crops and the diversity of food sources for the expansion of the microbiome population could be contributing to increases in soluble P if the soil is aerobic enough to make it really happen. Most long term no till plow Layer deep and even 0-3 inch profiles do not show significant increases in P1 if any at all. It is the exception and certainly not the rule.
In the exceptional cases, if the main crop and cover crop root systems fail to establish root mass beyond 3-5 inches the soluble P compounds could make it to the tile.
The observations of soluble P in drainage water is really a kick in the shins of no - till or at least a serious indictment that all is not well for the no - till advocates. For example, Root system total mass may equal conventional tillage mass but the distribution of the mass is not good for accessing capillary water and soluble nutrients contained therein. Purdue study dating back to the 80's. The same silt concentration which produces shallow root systems also prevents capillary water movement. I call it "isolation" syndrome; stark contrast to "association" syndrome.
Secondly, SOM does increase the water holding ability of soil. If no till soils really do increase SOM to any significant extent through the plow layer ( not confined to the top 2-3 inches where we typically see it) then the amount of water leaving the farm in tile drains ought to be less every year. The lowered amount from tiles should not be accompanied with greater run-off rates. I'm afraid greater run off is a reality and is the true source of the most problematic issues of P in our freshwater streams and lakes.
The sulfur problem is very real and also aggravated by poor rooting depth. The plant will recycle nutrients if it accesses them. How much sulfur from subsoil can be recycled if plant roots don't get there or capillary water can't move the soluble minerals like sulfur upward to the roots?
Reminds me of your favorite phrase....Covers need to OCCUPY the soil.
Here in the high plains the water collects where it can't run off the field in Sodic and non Sodic sloughs. Doesn't take more than .2 BS sodium to create Sodic sloughs. Seeing it is believing it can be done. Amazing. The infiltration is really good (3-4% SOM) but the percolation stops at 2-3 inches. Horizontal flow ensues with transport of soluble sodium salts.
In one growing season with 14 inches of precipitation we have seen the sodium surface disappear from sloughs. Two things happened. No additional sodium was transported from higher soils surrounding the slough. The precipitation leached the sodium contained in the sloughs. I drove right through sloughs with combines and the CurseBuster this fall where the neighbors would have been looking at standing water on their farms in SK.
I hope some of the folks cc'd on this will hit "reply to all" with their comments.
Happy New Year, Dave, and God bless.