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Q #1 on Soil--25% organic matter ideal by weight or volume?

Posted by reyesuela z7a (My Page) on
Mon, May 16, 11 at 13:58

I got some soil brought in for raised beds that was 50% screened top soil (around here, read CLAY) and 50% composted leaf mould by volume. I've heard that 25% OM is ideal. Is that supposed to be weight or by volume? I want to see what I need to add next year. I'm going to top off the beds (because of settling and decomp) with more 50/50 by volume mixture, but if that's close to the ideal, I'm using only compost after that.

Next year will be more leaf mould mixed with top soil, but after that, I should be able to produce a large proportion of the compost I need from our leaf mould and kitchen scraps and then get composted horse manure to fill up the rest of my needs for free (but I have to haul it!).

Thanks!!!!


Follow-Up Postings:

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RE: Q #1 on Soil--25% organic matter ideal by weight or volume?

volume


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RE: Q #1 on Soil--25% organic matter ideal by weight or volume?

Optimal levels of organic matter in soil fall in the 5 to 8 percent range, 25 percent is getting close to swamp land. Most every soil lab will tell you that anything much over 5 percent is too high.


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RE: Q #1 on Soil--25% organic matter ideal by weight or volume?

I think the person who said 25% was probably talking volume, since that would typically be pretty close to the 5 to 6% range by dry weight. Of course it varies a bit depending on the bulk densities of the soil and the amendment but it's a decent rule of thumb.
For example, if you had a soil with a dry bulk density of 2400 lbs per cubic yard and an organic amendment with a dry bulk density of 425 lbs. per cubic yard in a 75/25 blend by volume, the o.m. in the blend would be 5.6% by dry weight.


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RE: Q #1 on Soil--25% organic matter ideal by weight or volume?

Excellent. That's what I assumed, but I wasn't sure.

I'm not worried about the 50% by volume right now because while it's composted, it'll still need quite a bit of degradation to be off to a good start. With all the settling, I'll see how much we need next year to top it off, and if that isn't sufficient, I'll add a bit more just plain compost on top.


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