RASH = Rapid Assessment of Soil Health
We do this to identify the condition of the soil and troubleshoot.
Q. What is the limiting factor of my soil?
Soil testing: NB. Have to do it at a reasonable level of soil water conditions. This is true for all soil monitoring. And be consistent. Always benchmark against soil of a similar type.
Texture Get your hands dirty.
Ribbon Test Squeeze a sample of soil with some water on it. Make sure roots and stones are removed, and able to handle without it sticking too much. Mash it up into a bolus (a cigar-shaped lump). Use a ruler. Squeeze to about 1cm wide and push out between thumb until it drops off (a ribbon) and measure how long the bit that dropped off is. Do it several times. This length is known as the ribbon length. Check against the charts in the Landcare RASH Manual.
Q. Does the ball (bolus) hold together? Is it very plasticeney? Does it collapse? You want it to be firm.
Feel it. Is there any sand or grit in it at all? Even a little bit. If you feel any grit at all then you should include the word 'sandy' in the name of the soil type.
Does it feel spongy? Does it feel silky? If it feels silky it is a silt.
These things tell you what the soil you have to play with is.
Equipment: A wire coathanger pulled into a square.
Q. How much of the soil is covered by grass/manure/rocks/litter/hay? Q. What type of ground cover is there? Q. How much actively growing grass is there (in the carbon growing season)?
Take the coathanger square and select a random sample of ground by throwing it over your shoulder to where it lands. Look into the square and estimate the % that is covered (not bare soil).
There is a smart phone app called 'Groundcover' from app store that you can use to do it, walk along and take photo of ground at your feet and it tells you the figure.
Infiltration of water into the soil
Equipment: A wide strong plastic pipe and a rubber hammer Something to measure a quantity of water A stop watch (can be a function on mobile phone)
Knock the plastic pipe into the ground a little with the rubber hammer to seal the ground surface. Pour a known amount of water into it. Use the stop watch to time how fast the water is absorbed. Faster is better. You can strip off the top layer of leafy grass, or cut the grass short before you do this if you like, or not.
Stability, strength, compaction
Air dry soil balls at least 24 hours before you do a soil structure test.
Crumbs are the primary building blocks of soil structure.
Equipment: Some little dishes. Distilled water or rain water. (Groundwater or spring water no good for this test) A thin strong steel rod to use as a penetrometer (we use a long smooth tent peg). A ruler Sheet of plastic or a plastic tub
Get a crumb of the soil, and gently pop it in a shallow dish of distilled or rain water. Water floods into all the air pockets in the crumb of soil. If the crumb still holds together then it has structural strength.
Q. Does the crumb break apart within 10 minutes? This is the aggregate stability test. The crumb that stays together longer is better. Falling apart fast indicates deep compaction of the soil - not what you want.
Slake test: Q. How big are the bubbles that are coming up out of the crumb as water filters into it? The bigger the bubbles the bigger the pores in the crumb, and the more organic content and activity it is, allowing it to hang together longer. We want to see the crumb retain its integrity.
Fungal hyphae weaving in and out of a soil crumb give it strength.
Penetrometer Push the penetrometer into the ground. You can pay a lot of money and buy one with a pressure meter attached. Quite a good measure is to use the palm of your hand and stop before it gets painful! 300Psi. Measure how far you were able to push the penetrometer into the soil (the length that is in the ground). Basically the deeper the better.
1.2metre drop test
Drop the clod of soil 3 times from a height of 1.2m (don't throw, just let fall) onto a large plastic sheet or into a plastic tub.
Sort the bits quickly in 2-3 minutes into large and small to give the crumb profile. You'd prefer the majority to be small crumbs.
You don't want to see loose powder. You want to see small crumbs. You don't want heavy clods.
A clump of soil has smaller units of structure. A clod of soil is a solid block, with less structure.
Dig out a 20cm by 20cm by 20cm cube of soil including the surface plants. Do so at a time of year with reasonable soil moisture.
Look at the roots. Look at how deep they go, how thick they are, and how dense.
Turn the sod upside down and look at the bottom. Q. Am I seeing 20+ roots at the 20cm depth level? If you don't see them at the 20cm level, shave 5cm off the bottom and ask: Am I seeing 20+ roots at the 15cm level? If not, shave off another 5cm from the bottom and ask again...
Next look at the root volume. Take10 root crumbs of reasonable volume and open them up. Q. Do you see any roots? Take crumbs from the 20cm level and do this. Do you see any roots? Take crumbs from the 15cm level and do this. Do you see any roots?....
Look at the roots sticking out of the soil. Q. What soil is stuck to the roots? Shake the root. Q. How much soil is still stuck on the roots? Soil that sticks to the roots indicates good biological activity happening. Heavy clay soil is more difficult to do this test as the soil can strip off.
Cotton strip test Can bury cotton strips in the ground and see how long it takes for them to biodegrade.
Tillage (diacom) radish are a cover crop designed to break through soil barriers. Don't feed them to milking cattle as it taints the milk, however cattle LOVE them. Ozwest Toowoomba sells the seed. www. tillageradish. com
Equipment: magnifying glass and possibly microscope. Tray.
Spread some soil out on a tray and look at it through a magnifying glass for 5 minutes. Q. What do you see? What organisms?
This takes PATIENCE. Give your eye about one minutes to adjust to the scale. Don't move your eye during that minute.
Equipment: ph meter; salinity meter. Distilled water
Drop a ball or crumb of soil into a bowl of water. Be gentle! If you do a drop test and the water goes milky, then the soil is probably sodic.
RASH = Rapid Assessment of Soil Health