PERFORMANCES OF SEED DRILL COULTERS IN RELATION TO SPEED, DEPTH AND RAKE ANGLES

The horizontal and vertical soil forces acting on coulters with rake angles of 70, 90, 110 and 130 ° and widths of 15 and 40 mm were measured to investigate the variation of working depth under various conditions. The measurements were made with extended octagonal ring transducers using speeds between 0·3 and 3·0 m/s and depths down to 70 mm both in dry sand in the laboratory and down to 45 mm in a clay field. Polynomials in one variable and in several variables were fitted to the measured data using statistical analysis. The relationship of force to speed was well described by a second-order polynomial. The quadratic term contributed far more to the fit of the model than the linear term. The relationship of force to depth was described by a second-order polynomial, but this polynomial had its intercept at the origin. Polynomials in the three variables rake angle, speed and depth were also fitted. These polynomials were used to investigate the influence of coulter and suspension parameters upon the variation in equilibrium depth when the coulter is subjected to varying working conditions. In sandy soils the variation in equilibrium depth decreased with increasing rake angle, while the influence of the suspension parameters was small. © 1992 Silsoe Research Institute.