The actual soil surface is indicated by the continuous black line, while the dashed line indicates the position of the original, eroded soil surface. The difference between both surfaces corresponds to the eroded soil profile.

Weed control in olive groves is necessary to prevent them from competing with the olive trees for moisture. In the 1970s, tillage with tractors became commonplace in Spanish olive groves. However, repeated ploughing left the soil loosened and torrential winter rains washed away the topsoil. Herbicide use has replaced tillage for weed control during the last twenty years and large reductions in soil erosion have occurred. A recent study determined that during the period of mechanical tillage, erosion rates were as high as 40t/ha/year while today, the erosion rate is 10t/ha/year.

“Olive orchards are an important agro-ecosystem in the Mediterranean. Soil erosion is a widely recognized threat to their sustainability. …This study aims at measuring and modelling soil erosion rates in olive orchards over a 250-year period, and relating these to changes in management practices and yield, as documented from historical sources. In three study areas in S-Spain, the height of relic tree mounds was measured in olive orchards dated between 153 and 291 years old to determine soil profile truncation. Historical documents allowed characterizing land management since 1752 in eight distinct periods.

Current soil losses by tillage are low because of the replacement of the spring tillage operations by herbicide application since the start of Period 8 in 2000. Only superficial harrowing is continued during summer. These superficial operations result in a lower movement of soil. In contrast, the highest soil erosion rates by tillage are found right after the introduction of mechanized agriculture, between 1970 and 1990 (Period 7), mainly because of deep mouldboard plowing, which is done at least twice a year.

Most of the tillage erosion occurred during periods of intense tillage, like from 1970 to 1990. To date, tillage is of minor importance due to the preference for herbicide use for controlling weeds.”

Authors: Vanwalleghem, T., et al.
Affiliation: Instituto de Agricultura Sostenible, Spain.
Title: Quantifying the effect of historical soil management on soil erosion rates in Mediterranean olive orchards.
Source: Agriculture, Ecosystems and Environment. 2011. 142:341-351.