Is there a test to get a percentage of organic matter in a soil sample? Anyone know how is this typically done in a lab? I was wondering if the sample is weighed, burned off, and re-weighed to calculate a percentage? I guess compost made from leaves, twigs, peat moss, grass would be close to 100% "organic matter." Sand, stones, clay, perlite, vermiculite, water, nitrogen salts would be "inorganic matter?" What I am hearing is that good soil must have greater than
Many labs test for this......its just a matter of finding one locally. The lab Victoria referenced is an excellent one and does go about it differently, using chemical extraction rather than burning, which is most common.
However, I tend to agree with Bill on this matter. It is difficult to overapply organic matter as it continues to breakdown and gets converted to other, essential elements. It simply doesn't last very long :-) And few soils tend to have an overabundance anyway, so routine applications of a compost or organic mulch of your choice or growing cover crops is generally advised for most home gardens and especially those that focus on harvested, edible cropping.
Yes. The sample should be taken with surface organic material scraped aside. Sample should be taken from a hole 8" to 12" deep (the material from that hole is your sample). For organic analysis, the sample would first need to be dried and weighed, then aerated and held at a temp greater than 455F for several hours, and then reweighed.
If you put a similar sample in a large jar with water and shake your sample until it forms a slurry, the sand will fall out after five min. or so, the silt after 20 min., and the clay after 24 hours (descending particle size). The height of each band in comparison to the total sedimentation will give you the approximate composition of your soil. Good soil will be 20 - 30% clay, 30-50% silt, 30 - 50% sand, and 5 - 10% organic material.
There is more about microorganisms and their interactions with plants but I've already gone beyond what you asked.
One cautionary note though, beware chemical fertilizers. This doesn't come from ridged ideology but from the facts that numero-uno: chemical fertilizers, used at suggested rates, kill off soil organisms, which leads to less top soil, which leads to the use of more chemferts to maintain production, and numero-two-o: the translocation of the nitrogen to the plants now rapidly growing leaves (nitrogen rich, tender leaves) makes them a target for garden insects.
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