CALCULATION OF THE NMIN TARGET VALUE (NMI N-SOLLWERT) IN VEGETABLE CULTIVATION WITH SPECIAL REGARD TO N-IMMOBILIZATION RESPECTIVELY N-FIXATION

When establishing target values for N fertilization (N(min)-Sollwert = optimal sum of soil mineral N at the beginning of cultivation and fer tilizer N) experimentally the components of the N balance are restrict ed to N(min) target value, N(min) supply of the soil and N fertilizer amount. In fertilization experiments any other processes in N dynamics are included in the target value without being noticed. If N(min) tar get values are to be calculated such simplified reflection is not long er possible. In this case the most important components of the N balan ce have to be determined and quantified. Up to now the formulas to cal culate the N(min) target value have included the N uptake of the crop (also called ''N demand''), frequently the necessary minimum mineral N content at harvest time in the rooted soil layer, sometimes the N rel ease during the cultivation period. Immission, denitrification, leachi ng and others during the summer half-year have been considered in only a few cases. Calculated N(min) target values from N uptake of the cro p plus necessary minimum mineral N content in the soil at harvest time minus N release yields in all cases studied distinctly lower values t han determining them by fertilizer experiments. Only if a calculated q uantity ''deficit'' is included a satisfactory agreement between the t wo values is attained. There are indications that this quantity consis ts mainly of temporarily bound or immobilized nitrogen.