Soil Air Porosity

Rain. Something we have not seen in a while, and it is glorious to see.
We are enjoying every moment as it falls from the sky and watching our systems return to life.
Unfortunately, that also means that with all this rampant growth. We cannot get into our gardens due to water saturation. That brings the question to mind with regards to water and our soils and their water holding capacity.
 In short – How do I know if my soils are over-saturated so that once this rain clears, we can get back into our gardens?

It is easy to get over-enthusiastic and plant to maximise our time and space. Still, suppose the soil is holding to much water. In that case, it can squeeze out air and become anaerobic, which can kill off or invite pathogens into our gardens, causing lots of issues.
 I was recently introduced to a simple test done in Horticulture to test the air porosity in seed raising mix and potting mix to make sure that it will provide a suitable environment for our seeds or plants.
 Asking if it could also be used for our garden soils, I was told that it could be, but people do not, and the numbers to measure would be different.

That was enough for me. There was a possibility. So, diving into some research, I found the figures that we can use. This simple test can also be applied to seed raising mixes and potting mixes but our garden soils as well – Perfect.
 First, we need to make the kit we will need to test our soils. Again, simple enough, and I found that I had most of what I needed already in the sheds resource (junk) pile.

First cut 2 pieces of 90 mm PVC pipe, both 12 cms long.
Then, finding a matching cap, drill 4 9mm holes in the bottom
Attach the lid to the base of one of the 90mm pipe sections until it is firm (and not going to fall off)
Heat one end of the second PVC pipe and then gently squeeze it over the top of the other 90mm piece until it is splayed and fits snuggly over the top of the first 90mm piece. The volume of the bottom section should be 680ml total.

The Test 

1. Place the top section firmly onto the bottom section
2. Moisten the soil you are testing until it has a good feel in your fingers
3. Place the soil mixture into the stacked sections of the PVC pipe to the top of the second piece
4. Drop the pipe form a height of about 50mm gently so that the soil in it settles (do not push down or compact)
5. Place the combined sections of pipe into a 9l bucket of water and then slowly fill the bucket, without pouring water into the soil mix, until the water level is equal to the top of the pipe sections (approx. 24cm)
6. Allow it to soak for 10 minutes
7. Gently remove the combined cells from the bucket and allow them to drain
8. Repeat the above twice more.​ 

8. Once you have finished doing it 3 times, remove the top section of the combined PVC and remove the excess soil above the bottom section
9. Cover the top of the base with either an old stocking or muslin cloth, and secure with a rubber band to hold in place
10. Place the bottom section back into the bucket and slowly fill with water again to a point approx. 30mm above the soil line
11. After 10 minutes, reach done with both hands and remove the bottom PVC section but have your fingers over the holes so that the water does not drain out
12. Place the water-filled section over another bucket or container and raise it and drain the water into the container beneath for approx. 30 minutes
13. Remove the bottom section and measure the volume of water that has drained from the soil
14. The air-filled soil porosity for your now test garden soil

The volume of water (ml) divide by the volume of the bottom section PVC pipe (680ml) x 100%
If this figure is between 10% and 30%, then your soil should be okay for you to plant. If more, then it is holding onto too much water and will cause issues to your plants. If under 10%, then it is not holding enough and needs to be addressed

All up, this test took me about an hour, but I could walk away and get other things done between the soaking and draining times.
It is something simple that can give us a lot of information. We can use it to provide us with the confidence to know if our water, air, soil ratios are good enough to plant and, if not, the knowledge to understand what we can do to improve them. 

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