Visual and smell test.
A simple visual check should show if the contents are dry. If dry it will also show no sign of decomposition, it will also lack heat, although
this test is not helpful if cold composting. If the compost is too dry it will lack heat and there will be little evidence of organic material break down. If you compost is too wet may appear slimy, be matted and smell unpleasant slight ammonia smell
indicating anaerobic decomposition
The Sponge Test
A simplest hands-on test is to take a handful of compost from between 18-24 inches into the heap or bin,
and squeeze it in a gloved hand. If the moisture content is between 40% - 60% it should react like a wet sponge staying compressed and releasing relatively little water.
The sponge test is difficult to use on the contents
of the top trays of a wormery, as it would involve squeezing and possibly killing the worms.
The sponge test provides a rough moisture measure but Will Bakx of Sonoma Compost has developed a system that refines the
sponge test and classifies the moisture content into seven categories based on the effects of squeezing the compost.
These ratings were confirmed as accurate by laboratory tests on the samples tested and the
ratings may need adjusting when applied to compost from other sources and interpreted by another other individual. The article appeared in BioCycle, a composting journal published monthly by The JG Press, Inc. in Emmaus, PA.
Sponge Test Moisture Estimates
Less than 40%. Compost too dry and does not form a ball when compressed and the hand is dry after discarding the material.
The compost forms a ball when squeezed but does not remain in a ball when the hand is opened.
45-45%. A ball forms when the compost is compressed but it falls apart if tapped with the knuckle of the other hand.
50-55%. The ball of compost stays intact when tapped but no water is visible on the hands
55-60%. The ball stays intact and sheen can be seen on the skin but no water droplets are produced
60% upper limit. Some drops of water are released when the ball is squeezed and can be seen between the fingers.
65%. The compost is too wet with water running between the
fingers when the compost is squeezed.
More details can be found at (http://sonomamg.ucanr.edu/Sonoma_Gardener_Articles/Measuring_Soil_Moisture_by_Look_and_Feel/
Compost moisture meters
A wide range of compost and garden moisture meters are available for the home composter at
between £7 and £40 this quick but not necessarily a very accurate measure. More accurate, and expensive, meters are available for commercial composters including digital recording meters.
As the moisture content
with varying in different parts of the heap or bin, it is recommended to take multiple readings and, so obtain a wider picture of the activity in the heap, temperature (and the pH) be recorded at the same time
I would recommend
using as long a probe as possible to reach the into the compost core of the compost and as well as the outer reaches. Most of the meters operate without batteries but some do require them. The cheaper meters often record on a scale rather than giving a direct
moisture level. In many meters will record temperature and pH as well as moisture.
The materials used in Vermiculture normally involves considerable variation in the moisture content of the feedstock with
pieces of material with a very high moisture content, such as food waste and fruit, mixed in the tray with drier material such as shredded paper and cardboard. This makes sampling water content with a probe difficult as the results will differ considerably
if the probe records the moisture from cardboard compared with the results from the centre of a piece of melon or pumpkin. This makes it essential to take a number of samples from each worm tray to give a representative result or to use the sponge
test in preference to a probe.
Drying to calculate moisture content
Moisture meters give an immediate reading but these are said to lack accuracy. If a more
accurate “laboratory” method is preferred (where the lab is the kitchen) the compost may weighed wet, dried and reweighed. Oven drying provides an accurate method for measuring compost moisture content but inaccuracies can be result
drying it at a so high a temperature as it loses organic material or burns.
- Weigh an empty ovenproof container of a suitable size to hold 10 -20g of
compost. It will help if three or four similar, containers where available for use.
- Add approx 10-20g of compost taken from a number of sites in the bin or heap and dry the compost thoroughly in the oven at low heat
overnight or until it ceases to lose weight.
- Weigh the dried compost
- Subtract the weight of the dry compost from the wet weight given the weight of the evaporated moisture.
- Divide by the wet weight and multiply by 100 to determine
the Moisture content.
- A variation of this technique is to adjust the weight of the wet compost to 10g when weighing. Dry the sample in an oven at 110°C for 24 hours. Reweigh the sample, remembering to subtract the weight of the container,
to obtain the dry weight. Calculate the moisture content as above.