When archaeological features are buried they can affect the growth rate of the crops above them. The presence of features such as buried wall foundations or compacted floor surfaces produce a reduction in the soil depth and lower moisture levels than the surrounding land. Crops immediately above these features tend to have reduced growth rates in comparison to the plants above of no archaeological activity, producing “negative cropmarks”.
In contrast areas where ditches, pits and other features have been dug into the subsoil become filled over time. This relative increase in soil depth and the potential to provide increased soil moisture enables the crops above to grow higher and ripen later than the plants around them, producing “positive cropmarks”. Both negative and positive cropmarks are more easily detected from the air and are usually visible during times of drought when crops are at maximum stress.
The articles have been written by Arcland members about Cropmarks.