If you’re getting sick of the compost tea debate then you can skip this post. If not, then read on!
This past week I received my copy of Arboriculture and Urban Forestry 37(6). And in it, page 269, I discovered an article titled “Laboratory Assays on the Effects of Aerated Compost Tea and Fertilization on Biochemical Properties and Denitrification in a Silt Loam and Bt Clay Loam Soils” by Bryant Scharenbroch, William Treaurer, Michelle Catania and Vincent Brand. Basically what the authors did was to add dilute compost tea, concentrated compost tea, and a fertilizer to a couple of different types of soil in a laboratory setting to establish how they changed the soil. To be honest the article was a little tough to read for a non-soil scientist and I found myself looking up terms quite often. Still, I found their conclusions fascinating. There were actually a number of conclusions, I’m just going to cover what I think are the most interesting:
- “Aerated Compost tea appears INFERIOR [you read that right – inferior] compared to fertilizer in its ability to increase microbial biomass, microbial activity” and a few other things. Hmmm…I’d been told that microbes hated synthetic fertilizer. I guess not all microbes agree. In terms of the fertilizer used, it was a 30-10-7. I didn’t see it explicitly stated in the article, but I’d bet it was a synthetic fertilizer called Arbor Green Pro. It was applied at what I would consider a heavy dose.
- Aerated compost tea, or at least the compost tea tested in this article, did contain a significant amount of nutrients.
- On the up side for compost tea it was pointed out that compost tea treatments might help a poor soil retain more nitrogen. Maybe…but the authors also pointed out that “only the fertilizer treatment appeared to deliver enough available nitrogen to potentially meet tree needs in the Bt horizon soils” (in other words poorer soils). Interesting – but if we just added compost we’d have a better soil anyway, which brings us to the next point….
- The compost tea tested contained only a small portion of the microorganisms that compost does.
So what’s the take home message from this article? This wasn’t explicitly stated in the article — in fact I’m not even sure the authors would agree with me — but to me the important message is 1) ADD COMPOST and 2) IF YOU NEED TO ADD NUTRIENTS ADD FERTILIZER NOT COMPOST TEA (though I’d go with a nice renewable organic rather than a synthetic).
Earlier this summer I took an organic farming course, offered through Georgia Organics. It was a delightful experience. And without a doubt, those that I was around hold compost tea in high regard. Personally, I just don’t want the extra work. If I can spread compost into my garden and let the rain do its thing and let decomposition and soil organisms do their thing, then I’m happy to leave nature well enough alone. But I think what’s at the heart of folks wanting to use this compost tea is that they believe it is fast acting (in delivering nutrients to the plants); and they believe they are capturing nitrogen when it is plentiful, early in the decomposition process. At least this seems to be the message conveyed to me…
Based on Julie’s comment, I have a question. How much nitrogen would be leached from barely broken down compost? And what form would that nitrogen be in? Wouldn’t any nitrogen leached from poorly broken down compost be organic as opposed to inorganic, and so not available
to plants anyway?
What was the recipe for “compost tea”. There are too many variables to establish any firm conculsions with what is offered here. I would agree that compost tea is not a magic bullet, but it delivers things fertilizers cannot..
I’m going to let Jeff answer Jimbo’s question, but as Jeff is in the thrall of grading papers, I’ll take Evan’s comment.
I was one of the reviewers for this paper, so I’ve seen it up close and personal. If you want to know how they made their tea, you should read the article. Jeff was merely summarizing some of the results, not offering an in-depth analysis.
For the most part, dilute compost tea treatment was no different than water in changing soil chemistry. Concentrated compost tea changed a few things, but none of them were particularly interesting or connected to one another.
The only “things” that I thought compost tea delivered in this article were a dilution of nutrients (more in compost), a reduction in soil microbes (more in compost) and a pointless use of energy in formulating, aerating, and applying something that nature makes herself quite competently. In fact, this was one of my criticisms in my last review of the manuscript: “I’m still disappointed that the authors don’t note that ACT requires more resources to make and apply than water (these drawbacks are never discussed), and that compost itself would be a better source of nutrients than compost tea .”
i probably lean on side of gardening
with organic fertilizers..
thanks for review and discussion on this..
question? was there any discussion in article or thoughts here on worm casting tea? areobic/anerobic?
much thanks
Julie and Jimbo, sorry for taking so long to answer. Basically nitrogen isn’t very available to plants until it is converted to ammonium and then nitrate. Of course, once it’s converted to these ions, it is highly mobile. Barely broken down compost would not leach much nitrogen because microbes would be using that nitrogen to break down long carbon chains — in fact, it might even take up some nitrogen.
Today I was reading Green Industry PRO magazine, and wondered if you’d care to take a look at an article about a company in California that touts its “organic soil fertility management program”.
http://www.greenindustrypros.com/article/10416574/this-project-proves-it
Their program includes liquid organic fertilizers and compost tea, and a bunch of other ingredients that I’m unfamiliar with. I know that some parts of their program are sound, but I question whether others are scientifically valid , or if they’re just pseudo-science mumbo jumbo.
Hi Dave, My opinion, some is mumbo jumbo and some is sound — compost tea is mumbo jumbo, fertilizers are sound. The thing about the study they did is that they did some good stuff — and some silly stuff. The good stuff had an effect — and then they decided to credit the silly stuff.
Nice content.