Characterizing the bulk density of compost

The bulk density of compressible materials depends on the compressive load to which they are subjected. This results in bulk density variation within piles of such materials. However, it is difficult to measure bulk density i n situ without disturbing the sample or changing the load on it. A laborato ry method was developed to simulate the variation of density with depth of material. The method was used with compost, wood shavings, straw and peat a nd simulated material depths of up to 3.5 meters. The variation of bulk den sity with depth was shown to follow a power function relationship where the exponent provided an indication of the compressibility of a material. Effe ctive density is proposed as a useful single descriptor of bulk density. Bo th effective density and material compressibility were shown to be influenc ed by the size of container used to obtain measurements. A medium sized con tainer (400-mm diameter and 380-mm fill height) provided a good compromise between accuracy and practicality.