Jordan:

We have been discussing zinc issues in peanuts at the production meetings this year. It is important to consider the amount of zinc in waste, the uniformity of zinc in waste, and the rate of waste that is applied. In a previous Peanut Note we provided a newer recommendation.  If the soil pH is 6.5, it is very likely that zinc injury will be relatively minor if at all if the index is 750.  We are still working towards a more concrete recommendation, but the 6.5/750 thresholds seems to be reasonable. Of course, there could be hot spots if you are using an average number for the field.  Applications of waste tend to be non-uniform.

I discussed how one calculates zinc in waste and then how that information is used to make sure waste application does not render fields useless for peanut production.

Here is a part of that discussion with a link to other resources provided in an earlier Peanut Note.

Kulesza:

It’s hard to estimate how an application of zinc will affect the soil Zn-I. The most conservative estimate is to assume all of it will be available. To do this, you would divide the pounds of zinc applied per acre by 0.071 to get the increase in zinc index.

I found the conversion factor on the NCDA&CS website.

So, if you’re applying 500 lbs/ac of the first sample (4.5 lbs of Zn/ton), you’d have a maximum soil Zn-I increase of 15. Notice that the three waste analyses are very different in their zinc concentration. It’s really important to have an accurate analysis of the product that you’ll actually be applying to avoid a toxicity issue.

Read more at: Estimating Zinc Index Values