A FLEXIBLE FUNCTION FOR REGRESSING ASYMPTOTICALLY DECLINING RESPONSESOF PLANT-GROWTH TO GROWTH-RETARDANTS

A modified power function, y = (A + B.x)(-C), was developed for determ ining the relationship between plant growth and growth retardant treat ment. This function accounts for the plant response characteristics by incorporating three coefficients: A, growth level of the nontreated p lants; B, the degree of growth reduction; and C, the smallest effectiv e dose of the growth inhibitor. The function accounted for 97 % of the variation in purple nutsedge (Cyperus rotundus L.) leaf length as a f unction of the amount of a growth retardant applied. The procedure res ulted in a smaller error sum of squares than several common nonlinear functions because of its greater shape flexibility.