Soil amendments: Now, with SCIENCE!

They say you’re supposed to get a soil test every three years. I’d gotten one the spring of 2010, right after the land was cleared, but it was an over-the-counter sort of thing and told me nothing beyond soil ph (backfill hill, 5.1; bottomland 5.5). I was of the opinion that if I just kept adding more organic matter to the soil, plus a bit of lime here and there, it would all work itself out eventually. And it seemed to do pretty fine. Things haven’t grown as big as they could, but then the groundhogs and deer mostly cut them down over and over, so that might have been the reason why.

Then I heard this fascinating two-part podcast interview with Steve Solomon over at The Ruminant (which is a great garden hacks blog, by the way).

Solomon maintains that food cannot be nutrient-dense if it comes from soil that is nutrient-poor; that even if it produces fruit, those fruits will be lacking in vital minerals and elements that we humans need. He talks about his newest book, The Intelligent Gardener, which sounded so interesting that I immediately requested it through inter-library loan (I’ve learned the hard way not to buy books I haven’t read before).

It’s a good book. Solomon starts by assuming you have next to no gardening experience, but also directs you to different chapters based on your experience level. He goes in-depth into soil science, about the roles that each mineral has to play and the optimal ratios and complex interplay between them in the garden.

To be honest there was so much science that by 3/4 through the book my eyes kind of glazed over at times; his jovial (and somewhat curmudgeonly) tone kept it light though.

While I was waiting for the book to arrive, I finally got on the ball and ordered a pair of real soil tests from A&L Eastern. (I’ve been really happy with these guys; they’re cheap, fast, and when a few days after I got the results I realized that I’d ordered the wrong test, they still had my samples on hand and went ahead and emailed me the results for the new test right away and said I could call them whenever to settle up the difference. It’s nice to find trust in a commercial company like that, and I’ll be using them from now on.)

I was surprised, first, that in both samples my ph had improved a lot (backfill hill 6.5, bottomland 5.9); and secondly by how much – and by what – the soils were lacking. Iron is off the charts, but we have next to no sulfur. I never would have thought sulfur was very important.

Solomon quotes the old economic principle that growth is limited by the scarcest element. His entire book is aimed at getting my soil minerals in balance – his term for that is remineralization – so that the plants can have plenty of everything they need in order to grow their best and provide the most nutrient-dense (and tastiest) food. In order to arrive at a balanced soil, first one must translate all those ppm numbers listed on my soil test results into actual pounds per acre of elements that I need to apply. That involves math. Math and I do not get along.

Luckily, Solomon also provides simple worksheets in the book. He has generously also made them available for download at the New Society website.

I had some pretty huge deficits, according to Solomon’s math. The numbers on the far right are the pounds per acre of actual element; you can see below how I translated that into pounds of actual fertilizer (divide by the percentage listed on the bag).

As you can see by my results, I would have needed 261 pounds of kelp meal, 30 pounds copper sulfate, 108 pounds bone meal, along with some other stuff too. And these totals are just for our bottomland; half (I omitted the pathways) of 3/4 (Backfill Hill takes up the rest) of 1/4 acre.

Well, I hate to disappoint Solomon’s contention that anyone not on a commercial farming scale can afford to remineralize, but dude, that just ain’t so. Copper sulfate is $33 per 4lb around here; kelp meal is sold in 5lb bags for $20. I didn’t even bother to calculate out the cost for the ideal remineralization program – I just laughed and bought what I could afford. A little is better than nothing.

Plus, I’m leery of overfertilization. Solomon’s recommendations were up to 800% greater than those given by the soil lab. Not that these particular fertilizers are anything to really be scared of runoff-wise; minerals and bone meal and greensand will stick around for quite a while. Which is, I guess, the whole point. Even so – easy does it, eh?

I had already put down 90lbs of lime; I added 50 lbs bone meal (half what was called for), 133 lbs greensand (very cheap but very, very slow to release), the borax & epsom salts (Mn sulfate) but no copper sulfate (my farmer friend at the local feed store said it’d kill my crops) and no zinc sulfate (couldn’t find it and didn’t need enough to bother). Up on Backfill Hill I added 3 lbs sulfur, more epsom salts & borax, among other things. I mixed each prescription up in my wheelbarrow, poured them into my spreader (using it for the first time in three years) and applied liberally on the beds, then tilled.

I hope I did it right. I hope Solomon knows what he’s talking about. I hope I haven’t just poisoned my whole garden.

Time will tell, I suppose. If things grow great this summer, I’ll give Solomon a little more credit than I already do. And I can’t wait to see the difference in next year’s soil test.

2 Responses to “Soil amendments: Now, with SCIENCE!”

  1. Erin Says:

    Sounds very interesting! We had a soil test when we moved in and things grow so well here but the nutrient factor is something to think about!

  2. Diana Guillermo Says:

    Yeah, things grow so very well at your place that it’s kind of like… why mess with them? Things were obviously off over here, plants just not growing well, etc.

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