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Percent Organic Matter

Posted by mrpeach (My Page) on
Thu, Apr 2, 09 at 11:31

I just had a soil test done on my lawn and the % organic matter came back as 2.5. Does anybody know what is ideal? Also the pH is low. Can I apply a liquid calcium to help raise it?


Follow-Up Postings:

RE: Percent Organic Matter

Congratulations Mr. Peach on getting a soil test. 2.5 % organic matter is pretty good. 5 % is said to be ideal. Lime is the usual product used to raise the pH. Im no expert on soil analysis but Andi is. He will be along soon to help you out. Could you possibly scan youre test results and post them here, or just post the numbers, Usually soil tests give recommendations. Did yours?
Bill Hill

Here is a link that might be useful: Soil Management part 1

RE: Percent Organic Matter

Mr. Peach:

A 2.5 reading for Soil Organic Matter (SOM) is on the low side of medium for unamended soil. Soil tends to run from 1% in very sandy soils to 5% or so for older grassland. But (and it's a big but) there is a lot of variability of results due to the method used to do the analysis. You may want to find out what method was used for your test and post it here - it would definitely affect my response.

About the Lime (its one of my favorite subjects) - Lime is way more complicated than the big-box stores would have you believe. There are Limes that are very-low in their Magnesium content and Limes that are very-high in that regard. I've come to believe that the Calcium/Magnesium ration has WAY more impact on overall soil/lawn health than anything other than the Nitrogen level. Post you Calcium reading, your Magnesium reading and the pH and I'll make a recommendation or two.

Read the article that Bill linked and you'll understand my answers a bit more...

RE: Percent Organic Matter

Optimal levels on organic matter in soils would be in the 6 to 8 percent range and the optimal soil pH range would be in the 6.2 to 6.8 range, where most all nutrients are available, although some plants prefer a lower pH.
Calcium, no matter which you use, takes time to work, liquid wil be no faster than pelleted. Some simple soil tests you can do that will help you understand your soil more are,
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer you soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.
The 4 inch level in the Jar Test makes the math a lot easier, with other levels there are conversion factors to use.

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