Zinc Discussion

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E-mail string Relative to Zinc:

Note that there is a lot here. Start from the bottom. Not sure you are interested in this but David Hardy provided an excellent overview of zinc toxicity.

On Jul 24, 2015, at 1:37 p.m., Tommy Cleveland <Tommy_Cleveland@ncsu.edu> wrote:

Wayne, David, David, and others,

Thank you all for this input, it has been very helpful for me. It gives me a decent understanding of the issue and how likely it is to be a problem for solar farms. Is the following a fair summary of your understanding of the situation? I welcome any improvements to the wording, especially the last sentence. I hope to include this in a list of FAQ about impacts of solar farms in NC.

The hundreds to thousands of small galvanized steel posts that support thousands of PV panels in a typical multi-megawatt solar energy facility will slowly release small amounts of zinc in the immediate vicinity of each post over its decades of operation. High levels of zinc in the soil is known to stunt plant growth, which most commonly occurs due to heavy application of swine waste or sludge, and peanuts are much more sensitive than most other crops. Based on research on soil impacts of galvanized transmission line support towers, local experience with galvanized roofs, and input from NC State University soil scientists it is expected that the zinc released from a solar installation over its operable lifetime would have an insignificant impact on future agricultural use of the site, with a possible exception for a potential for some impact on peanut production.

Thank you all,


Tommy Cleveland, PE
Renewable Energy Project Coordinator
NC Clean Energy Technology Center
NC State University
919.515.9432 (office)
919.923.5490 (cell)


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On Thu, Jul 23, 2015 at 11:08 a.m., Wayne Robarge <nwpr@ncsu.edu> wrote:


I think David Hardy has summarized situation very well.

I would expect “drip” from any overhead galvanized metal to elevate the Zn content of the soil. We see this in the greenhouse as anyone knows who has a trial sitting under the overhead metal frame work that might be galvanized metal.

As David Jordon has noted, we often get calls about small “hot” spots from down spouts of old buildings that were once on the property with galvanized roofs.

If the pH is adequately maintained and the soil mixed – tilled – every now and then, I would assume the issue will not be of major concern. But I assume as well this depends on the quality of the galvanized metal.

It is also good to pay heed to David Hardy’s explanation that Mehlich III is not a total elemental analysis. It is a test of availability for plant growth. Sometimes people will send a sample to a commercial lab and the lab will do a total elemental analysis. I would expect the total Zn content of the original soil might be higher than what is indicated by the Mehlich III extraction.

This might confuse people who think they have a problem when in fact they probably do not.

Wayne Robarge

On Jul 23, 2015, at 8:23 a.m., David Jordan <dljorda2@ncsu.edu> wrote:

Thanks David! We see places in fields where old buildings were located and the injury is often below the roof line where water ran (including zinc.) These lines are really bad but they don’t seem to change over the years. They may get a little bigger with tillage but they seem to stay very localized.

On Jul 23, 2015, at 8:12 a.m., “Fish, Ron W” <ron.fish@ncagr.gov> wrote:


Thank you for your thorough response. This was most helpful.


From: Hardy, David H
Sent: Thursday, July 23, 2015 8:00 a.m.
To: Hardee, Dewitt <dewitt.hardee@ncagr.gov>; Theodore Feitshans <taf@ncsu.edu>
Cc: Tommy Cleveland <Tommy_Cleveland@ncsu.edu>; Fish, Ron W <ron.fish@ncagr.gov>; David Jordan <david_jordan@ncsu.edu>; Dean Hesterberg <sscdlh@ncsu.edu>; sscwpr Robarge <wayne_robarge@ncsu.edu>
Subject: RE: zinc soil toxicity from galvanized steel

Peanuts are the most sensitive agronomic crop that I am aware of. We do not advise planting peanuts when soil test levels of Zn are around 250 or above; this number is our Zn index (Zn-I) using Mehlich 3 as a soil test extractant. A Zn-I of 250 is equivalent to 10 ppm in the soil. When data are compared in literature or from other labs, it is important to remember that different extractants extract varying amounts of elements in soil, so 10 ppm from Mehlich 3 may not equal 10 ppm from others…..

Management of pH that controls metal solubility in soil and the availability to plants is very important. Soil type (clay and OM) factors too and one would expect less likelihood of toxicity in soils with higher clay and OM content. These constituents of soil can bind the metal and lower its availability.

For other crops, Zn-I levels in the 2000 to 3000 and above warrant concern. Soil pH is very important too!

We have typically seen Zn toxicity in crops where application of swine waste (many years) and over application of sludge have occurred. We also see toxicity as related to old building sites where tin roofs were used. There have been cases too where piles of debris have been burned using and tires (steel belted). The worse situations appear to be where over application of sludge has occurred; in such cases, we have seen sites over the past few years where crop failure was widespread in fields. As peanuts have moved into areas of the state where they were not traditionally grown, we have seen more concerns in this crop.

In this situation, I would not expect much outward movement of zinc from soil from where the pole actually is; here I am talking about lateral movement. I would think the soil at the outer edge of the poles would become elevated in zinc over time but areas away from the posts would likely be insignificantly affected. Some rainfall hitting the posts could over time “splash” Zn around a small zone too. In considering a site, I think you have to consider the number of posts in a system. Some monitoring could be fairly easily done at sites before and after installation to get a better handle on this. These are just my thoughts with some speculation……It does appear that the data from the link at the bottom of this email supports my thoughts.

David Jordan is copied here and also I have copied Dr. Dean Hesterberg and Dr. Wayne Robarge, who are two excellent soil chemists at NC State Soil Science. They all may have different ideas.


David H. Hardy, Ph.D.
Section Chief- Soil Testing
Agronomic Division, NCDA&CS
4300 Reedy Creek Rd.
Raleigh, NC 27607-6465
919.733.2837 (fax)

NCDA&CS – Where Cultivating a Culture of Safety Is Everyone’s Responsibility!

E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed to third parties.

From: Hardee, Dewitt
Sent: Wednesday, July 22, 2015 7:48 p.m.
To: Theodore Feitshans <taf@ncsu.edu>
Cc: Tommy Cleveland <Tommy_Cleveland@ncsu.edu>; Fish, Ron W <ron.fish@ncagr.gov>; Hardy, David H <david.hardy@ncagr.gov>
Subject: Re: zinc soil toxicity from galvanized steel

Suggest talking with Dr. David Hardy at NCDA&CS Agronomic Lab Sent from my iPhone

On Jul 21, 2015, at 4:13 p.m., Theodore Feitshans <taf@ncsu.edu> wrote:

I would not expect solar farms to introduce enough zinc to be a problem but I don’t know. Peanuts are among the most sensitive crops. David Jordan <https://www.ces.ncsu.edu/profile/david-jordan/> is our peanut specialist. He would be a good person to start with.


Theodore A. Feitshans
Extension Professor and Director, ARE Distance Education Program
Department of Agricultural & Resource Economics, North Carolina State University Room 3340 Nelson Hall, Campus Box 8109, Raleigh, NC 27695-8109

FEDEX Mailing Address: Theodore A. Feitshans, NCSU – Dept. of Agricultural & Resource Economics, Room 3340 Nelson Hall, Raleigh, NC 27695-8109
UPS address:Room 3340/ Nelson Hall, 2801 Founders Drive, Raleigh, NC 27607

Phone: (919) 515-5195
Fax: (919) 515-6268
E-mail: taf@ncsu.edu
DISCLAIMER: Information provided is for educational purposes only; nothing herein constitutes the provision of legal advice or services, or tax advice or services, and no attorney-client relationship is formed. E-mail correspondence to and from this address may be subject to the North Carolina Public Records Law and may be disclosed, if permitted by law, to third parties. All e-mail to and from this address will be archived for a minimum period of 10 years.

On Tue, Jul 21, 2015 at 1:37 p.m., Tommy Cleveland <Tommy_Cleveland@ncsu.edu> wrote:


Can any of you help educate myself a little more on zinc toxicity for NC agriculture. I was recently asked by a farmer about the ability of the galvanized steel posts used in a solar farm to cause zinc toxicity in his field. It was not a topic I was familiar with, so I have done a little reading. From what I have gathered zinc toxicity can greatly reduce the production of soil if at high enough levels. These problem causing levels seem to come from industrial emissions, or long term use of fertilizer that contains a lot of zinc, like some manures or industrial sludge. I understand that the zinc in galvanized products does find its way into the soil over decades. From what I have read it does not appear that the zinc coming from the galvanized posts in a solar farm would release enough zinc to be of a concern for future crop production in that field, but I have not found any information that says that directly. What do you think?

Is there anyone else you would refer me to?

Thank you in advance for any insight you can provide. If a phone conversation will be easier than replying please let me know when I can give you call, or you could call me on my cell phone.

Here is the most helpful document I have found: http://www.galvanizeit.org/uploads/publications/Galvanized_Steel_Contribution_Zinc_Soil_Environment.pdf



Tommy Cleveland, PE
Renewable Energy Project Coordinator
NC Clean Energy Technology Center
NC State University
919.515.9432 (office)
919.923.5490 (cell)


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Article first appeared as North Carolina Peanut Note (PNNC-2015-088)