Wolf, D., Faculty of Agricultural Engineering, Technion Israel Institute of Technology, Haifa, 32000, Israel
Hadas, A., Division of Soil Physics, Institute of Soils and Water, Agricultural Research Organization, Bet Dagan, 50250, Israel

Heavy tillage implements, such as ploughs, used in semi-arid and arid regions are developed and produced for the temperate, humid regions of the world. Therefore, they are not operationally optimized for the air-dry soils on which they operate in arid or semi-arid regions, and their energy efficiency is not known. The experiments reported here attempt to determine the energy efficiencies of six types of moldboard plough when operated on brittle, clod-forming, air-dry soils. Energy efficiency is defined as the ratio between input energy and energy required for soil fragmentation. Input energy is given as the products of forward velocity and tractor draft, and the tensile energy required to fragment the soil and produce new surfaces is obtained from drop-shatter methods. The results show that no correlation could be found between energy input, plough characteristics and soil fragmentation. The results are explained by the fact that, in dry soil, fragmentation by ploughing is attained by tearing the natural clods from each other and by stressing them and translocating them, rather than by cutting, shearing and inverting the soil slices as is done in a moist, ductile soil. © 1987.