Monday, July 20, 2015

Soil Sediment Home Test

Sediment or tilth test. Why? So that I can evaluate the effect of my garden amendments, Since soil structure has a bearing upon soil moisture & nutrient retention, I am aiming for soil that is desirable for the type of plants I am growing. 

Home test, why? I could always just send a soil sample off to a lab, but why? I don't need super accuracy, nor do I need to give my hard earned cash to a lab several times a year. A low tech home test is just fine for my purposes. Besides, I test each garden bed at least once a year, so that's a lot of tests. 

What I need.....sool sample, straight sided, flat bottomed clear jar, ruler, dish soap, calculator if I'm not up to snuff about using my brain to do the math that day.

Collect sample

First, choose a representative soil sample. Should be from the plant root zone. Since my garden soil is mixed well the top six inches but often has a mulch cover, I will scrap away the mulch and the top 2-3 inches of dirt, then take my soil sample. 

Amount.....enough to full my jar by 1/3. I'll spread the soil sample out onto a flat plate or tray to dry. Once dry, I'll crush and soil clumps and put the soil through a sieve or colinder. I want to remove any pebbles, roots, etc. 

Next I'll put the soil into my large jar. As I said, I'll fill the jar 1/3 of the way. Then if I have it on hand I'll add a heaping teaspoon of dry automatic dishwasher soap. This helps get the soil particles wet and separated, but with my soil type I haven't found it to make much difference. Now I'll fill the jar with water within an inch or so of the top, put the lid in tight, and give it a good shake to get all the soil wet and suspended. I'll take care to make sure nothing is left stuck to the bottom or sides. Then the jar gets set on a flat surface so that things can settle. 

Layers will now develop. Coarse sand settles first and within the first minute. At no more than two minutes I use a marker to note the top of this sand layer. 
The sandy layer will look coarser than the silt and clay layers. 

Silt is the next layer to settle out. This will take about an hour to form. It will be a different colored layer. Most people say that their silt layer is darker than the sand layer, but here my sand comes from dark lavas, so my sand layer is darkly colored. At one hour I will mark the line of the top of the silt layer. 

Clay is the slowest of the soil particles to settle out. Heavy clay layer will settle out in a day, finer clay in two days. Some people say to allow clay to settle for a week but I haven't found that to make a significant difference on my home tests. I suppose it matters if ones soil had lots of fine clay, but mine doesn't. 

I use a tongue depressor to mark my layers, but you don't have to. I just happen to have thousands of the little buggahs in hand, so they are handy. I will then measure the depth of sand, silt, and clay, as well as the total soil depth in the jar. These measurements are used to calculate the percentage of each soil component.

For example, the jar above shows 2 1/4 (2.25) inches of sand, 1/2 (0.5) inch of silt, and 1/3 (0.33) inches of clay, for a total of --------3.08 inches. Divide each particle depth by the total soil depth to get the percentages:

2.25 divided by 3.08 = 0.73 or 73% sand 

0.5 divided by 3.08 = 0.16 or 16% silt

0.33 divided by 3.08 = 0.107 or 11% clay. (I rounded to the nearest whole number)

1 comment:

  1. So you're testing how much sand, loam and clay you have in your soil? No capice.