|MadSci Network: Agricultural Sciences|
Sorry about this somewhat delayed answer. I hope I am not to late. I am not sure what kind of dirt you refer to but I assume it is a soil used for agriculture, gardening or forestry. pH is an important quality measure of soil. It gives indications on how available for plants different nutrients apparent in the soil are. For agriculture and gardening the ideal often is around 6.5. However, there is also many other important soil characteristics. For example the organic matter content which is a source for many nutrients and also improves the structure of soil, so that the roots easily can penetrate. A simple estimate for this is the color of the soil (the darker the higher the content). For the structure of the soil the clay content is also important. This can be tested by forming crumbs of the moist soil. If the soil will fall apart no matter what you do the clay content is very low and the soil can not aggregate. If you can form very thin threads by rolling it between your flat hands the content is high.
You can find more information about the things above and other simple soil tests on: http://www.eosc.osshe. edu/peers/lessons/soils.html
On http://www.agri.upm.edu.my/j st/soilinfo.html you will find links to just about anything regarding soil.
Good luck with your project. Bosse
Try the links in the MadSci Library for more information on Agricultural Sciences.