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What is compost?

Gardeners and farmers improve the quality of their soil by adding compost. Compost is made from dead plants. Once spread on the soil, compost is broken down into minerals by decomposing bacteria and fungi, as well as by other organisms, such as worms. Adding compost helps to recycle minerals so that they are absorbed by new plants and used in growth. Compost also improves the quality of soil by increasing aeration and water retention.

The most favourable conditions for composting

Compost forms through decomposition. Therefore, the factors that affect the rate of decomposition also affect how quickly compost is formed.

Gardeners often make compost in a compost heap or bin. To speed up the rate of decomposition the conditions inside are kept:

1. Warm - compost bins are usually black, which absorbs heat. Heaps are often covered with an old piece of carpet to insulate the compost.
2. Moist - water is added at regular intervals.
3. Aerated - the compost is regularly 'turned' with a garden fork to mix up the contents, prevent the contents becoming compacted and to introduce oxygen.

Investigating the best conditions for composting

An investigation can be carried out to find the factors that affect the rate of decomposition.

A suitable method would be to place grass clippings inside black bin bags and place a thermometer in the neck of each bag before sealing.

The conditions can be changed for each bag. For example, you could add dry grass clippings to one bag and damp clippings to another. The bags are left in the same conditions and the temperature recorded at regular intervals. As the grass decomposes, the temperature will rise. The largest rise will be seen in the bag where the grass clippings have decomposed the most.