From the antiquity, the hilly landscape around the city of Axum in northern Ethiopia has been terraced and extensively used for agriculture purposes. The traditional “ard” plough seems to have been introduced in Ethiopia between 1000 and 400 BC. The impact of the plough against stones protruding and/o buried at a depth lower than the tilling depth produces a scratch on their sides or their top. The spatial relationship among plough marks and rock surface orientations gives information on the ploughing direction, whereas, if information about the age of cultivation is provided, the relative height from the present ground surface to the top of the marks can be used to assess soil loss rates. A few parameters to define the plough marks orientation were defined and measured in the field selecting a number of stones with plough marks within a study terrace located in an archaeological area of known age. These parameters are height from the ground, dip, slope and frequency. In this paper plough marks have been used as an innovative method to asses soil erosion rates and to reconstruct the original terrace slope and ploughing direction. The data measured clearly show that the initial terrace slope was steeper than the present one confirming the effectiveness of the traditional terracing practice in soil conservation because of the low soil erosion rates assessed over a so large time interval. For the main time intervals of the Axumite history, corresponding to the rise and fall of the Axumite civilization and to variable conditions of human pressure on the land, the maximum erosion rates inferred is of the order of 3.4 Mg ha-1 yr-1. This result is compared with erosion rates calculated with other methods reported in the literature (e.g. PSIAC) and field measurement on terraces in the same region leading to values almost coinciding with those obtained by the plough marks method.
Plough marks as a tool to asses soil erosion: a case study in Axum (Ethiopia)
BILLI, Paolo;
2008
Abstract
From the antiquity, the hilly landscape around the city of Axum in northern Ethiopia has been terraced and extensively used for agriculture purposes. The traditional “ard” plough seems to have been introduced in Ethiopia between 1000 and 400 BC. The impact of the plough against stones protruding and/o buried at a depth lower than the tilling depth produces a scratch on their sides or their top. The spatial relationship among plough marks and rock surface orientations gives information on the ploughing direction, whereas, if information about the age of cultivation is provided, the relative height from the present ground surface to the top of the marks can be used to assess soil loss rates. A few parameters to define the plough marks orientation were defined and measured in the field selecting a number of stones with plough marks within a study terrace located in an archaeological area of known age. These parameters are height from the ground, dip, slope and frequency. In this paper plough marks have been used as an innovative method to asses soil erosion rates and to reconstruct the original terrace slope and ploughing direction. The data measured clearly show that the initial terrace slope was steeper than the present one confirming the effectiveness of the traditional terracing practice in soil conservation because of the low soil erosion rates assessed over a so large time interval. For the main time intervals of the Axumite history, corresponding to the rise and fall of the Axumite civilization and to variable conditions of human pressure on the land, the maximum erosion rates inferred is of the order of 3.4 Mg ha-1 yr-1. This result is compared with erosion rates calculated with other methods reported in the literature (e.g. PSIAC) and field measurement on terraces in the same region leading to values almost coinciding with those obtained by the plough marks method.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
