1. Factors and indices regarding excessive compactness of agricultural soils;Canarache;Soil Tillage Res.,1991
2. World Resources 1992–93,1992
3. ISTRO, 1993. Extended abstracts ISTRO Workshop Soil Compaction and the Environment. Proc. Int. Conf. Protection of the Soil Environment by Avoidance of Compaction and Proper Soil Tillage, 23–27 August 1993, Melitopol, Ukraine. Melitopol Institute of Agricultural Mechanization, Melitopol, Ukraine, Vol. 2, 44 pp.
4. World Map of the Status of Human-Induced Soil Degradation, An Explanatory Note;Oldeman,1991
5. The European Soil Resource;Van Lynden,1994