Kalkulatorische Ermittlung des Nmin-Sollwertes im Gemüsebau unter besonderer Berücksichtigung der Stickstoffimmobilisierung bzw. - fixierung

Calculation of the N_min target value (N_min-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 fertilizer N) experimentally the components of the N balance are restricted 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 target values are to be calculated such simplified reflection is not longer possible. In this case the most important components of the N balance have to be determined and quantified. Up to now the formulas to calculate 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 release during the cultivation period. Immission, denitrification, leaching 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 crop plus necessary minimum mineral N content in the soil at harvest time minus N release yields in all cases studied distinctly lower values than determining them by fertilizer experiments. Only if a calculated quantity “deficit” is included a satisfactory agreement between the two values is attained. There are indications that this quantity consists mainly of temporarily bound or immobilized nitrogen.