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The prototype rotary blade with relief angle at the straight blade portion 1° (rotary blade B2) and 3° (rotary blade B3) were fabricated to study on the effect of the relief angle at a straight portion of rotary blade on the torque characteristic and the specific tilling energy to reduce the power used by rotary tiller for soil preparation, comparing with the European C-shaped blade (rotary blade B1). The experiments were tested at the soil dynamics and it’s application laboratory, Department of Agricultural Engineering, Faculty of Engineering at Kampeang Sean, Kasetsart University. The research works was conducted in soil bin at forward speed of 0.069 and 0.142 m s-1, rotational speeds of 150, 220 and 280 rpm in clay and sandy loam soils. The results showed that the torque characteristics of the rotary blades with relief angle at the straight blade portion 1° (B2) and 3° (B3) are such as the Europena C-shaped blade (B1). Besides, it showed that the relief angle at straight blade portion is the important parameter that cause the tilling energy decreased. The investigations showed that the specific tilling energy of the rotary blade with 1° relief angle at straight blade portion (B2) was the lowest while the specific tilling energy of the European C-shaped blade (B1) was the highest.