Author: Victor Jetten

Introduction
The eastern and central part of the Greek island Crete is suffering from land degradation problems, while the rest of the island is highly sensitive to desertification. Soil erosion due to surface runoff and tillage operations, collapse of terraces, overgrazing, salinization of lowlands, and overexploitation of ground water are the major processes of land degradation in the area. A lot of forested areas were converted into cultivated land in the last century. Overgrazing and fires further destroyed the natural vegetation cover and prevented its regeneration.

Olive groves are an important form of land use in the area, but have various degrees of due to the different land management practices. Farmers perceive an herb cover as a competition for water for the Olive trees and keep the field clean and bare below the trees. A minimum tillage experiment with and without herbicides was carried out to see if it is possible to maintain a soil cover, restore the natural soil structure, promote infiltration and reduce runoff and helps in minimizing soil losses. Overgrazing on the shallow stony soil decreases cover and destroys soil structure, and therefore promotes runoff and erosion. A grazing control experiment was done in this area.

The Olive area is moderately sloping land (up to 17%) with relatively deep soil (55-65cm). The overgrazed area has very shallow soils with frequent outcrops.

Desertification indices
Both areas are separately parameterized with water erosion and tillage erosion for the Olive field and water erosion and overgrazing for the rangeland plot.

Olives and minimum tillage: the overall unmitigated risk is moderate for water and tillage erosion on sloping Olive fields without soil cover and erosion control measures, and tillage operation to keep the area between the trees bare. Minimum tillage decreases the water erosion slightly and tillage erosion more (to low risk). The main factor here is setting the tillage operations from ploughing to none. Setting minimum tillage or no-tillage has no effect.

Olives unmitigated	Olives with minimum tillage

Grazing lands seem to have a low risk for water erosion and low risk for overgrazing. Increasing the vegetation cover by fencing the rangeland will correctly decrease both to a no risk level, but the change is not very large.

Grazing unmitigated	Grazing with rangeland resting

Conclusions
For Crete he observed changes are in line with the experimental results and are therefore correctly indicated, but not as pronounced as measured (up to a 50% reduction in runoff and erosion was seen). Also the over grazing risk reduction is correctly identified and in line with the experiments.

The assessment tool exhibits strange behavior that the setting of minimum tillage or no tillage has no effect on water erosion, but setting tillage operations form ploughing to none has.