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).