DETERMINATION OF OPTIMUM N-SUPPLY IN SUGAR-BEET BY DIFFERENT MATHEMATICAL-METHODS

Various mathematical models used to predict optimum N-supply (fertiliz er-N + N-min) for maximum root yield, sugar yield and white sugar yiel d were compared by fitting data from 39 field trials in Northwest Germ any (1980-1992). Quadratic, modified exponential and square root model s resulted in higher estimates of optimum N-supply than did 2-regressi ons and plateau type spline models with differences as high as 130 kg N/ha between models. Residual variance was lower with the latter two m odels. Data were grouped at 40 kg/ha intervals of N-supply for analysi s of variance and resulted in the lowest estimates for optimum N-suppl y. Based on the overall average, the optimum fertilizer-N dressings we re 80 kg N/ha for root and sugar yield and 70 kg N/ha for white sugar yield while mineral soil-N in spring was 70 kg N/ha.