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Silicon: Foliar vs. Soil Application

Posted by Brittany Kordick 
Silicon: Foliar vs. Soil Application
January 28, 2021 05:26PM
In recent years we have applied foliar silicon in the form of Sil-Matrix throughout the fruit sizing window. I've become increasingly interested in expanding our applications, starting soon after greentip, lasting until the leaves harden off, with the idea that the growing leaf cuticles have more constant and more consistent protection during the primary infection windows for so many of our arch-pathogens. We really like the Sil-Matrix formulation, but of course, there is huge added expense to upping the ante like this. I'm interested in playing around with bamboo teas at some point to see if we could find a way to meet our needs in a more localized, less expensive fashion, but that's not going to happen anytime soon, and in any case, it would take a lot of trialing and testing to convince us that a bamboo tea would give us the same bang we get for our rather large silicon buck with Sil-Matrix.

I recently discovered Wollastonite, a mined calcium silicate, that we would apply similarly to lime (1.25 times your recommended lime rate, according to application instructions). This option appeals for many reasons: we could apply it now, during the off-season, and silica/silicon is one less thing we have to worry about in our spray mix during the growing season; it's WAY less expensive; we'd also be applying some calcium at the same time.

Wollastonite is being touted for its silicon content, with the usual testaments to how supplemental silicon strengthens cell walls and stimulates a plant's natural immune responses. The company cites plenty of studies in its tech sheet to show how soil-applied silicon beneficially affects crops. However, I must admit, with all the recent debate over calcium mobility within a plant, I'm doubtful that soil-applied silicon versus foliar-applied silicon is entirely apples to apples. But even if we got a nice baseline with a winter soil application of silicon, and could reduce our foliar applications, either in rate or frequency, that would help.

Anybody out there have any experience with Wollastonite, or any thoughts about its potential virtues/vices?

Thanks

Kordick Family Farm
Westfield, NC
Zone 7a
Re: Silicon: Foliar vs. Soil Application
February 15, 2021 09:59PM
We talked to a grower rep at Vanderbilt Minerals to try and get some of the answers to our questions concerning Vansil wollastonite and its calcium and silicon availability, so just passing along what we found out:

Wollastonite is calcium silicate, and is not a soluble form of silicon. It is intended for long-term release. Calcium silicate has a pH of 10-11 and requires acidic soil to break down and release the elements. It's great for long-term, cumulative availability, much like rock phosphate. But it's self-limiting in the sense that, if you have acidic soil, and you're adding this very alkaline material to it, it will eventually be raising your soil pH to the point that the elements will no longer be able to be made available (but by then, you may have met your targets, depending on why you're applying it). We have an average pH of 6 in our orchard right now, and in addition to being after more of an immediately available silicon source, we are not interested in having quite such a heavy basic effect on our pH.

We're looking at AgSil, potassium silicate, as more of a readily available soil-applied source of silicon, but odds are we'll be sticking with Sil-Matrix and applying mostly foliar silicon in the short-term.

Kordick Family Farm
Westfield, NC
Zone 7a
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