Veränderungen des bodenbürtigen Mineralstickstoffs im Frühjahr und seine Bedeutung für die Bemessung der N‐Düngung von Zuckerrüben

Abstract

Abstract Dynamics of inorganic soil nitrogen during spring and its importance for N‐fertilizer management in cultivation of sugar beets High sugar yield depends very much upon application of the correct dose of nitrogen fertilizer. To determine fertilizer needs in sugar beet cultivation two methods – Nmin and EUF – are discussed at present. Both methods are criticized not to be able to take into account the amount of soil nitrogen which becomes available between the early date of soil analysis and actual nutrient uptake in the sugar beet stands.The objective of this study was to investigate the influence of varying N‐mineralisation rates on growth and yield of sugar beets and corresponding changes in N‐fertilizer requirements.The differences in soil nitrate content in February showed no relation to the amount on N available during the early vegetation period. Therefore very low correlation coefficients were observed between soil nitrate content in early spring (February/March) and sugar yield (R2 > 0.2). However highly significant correlation coefficients were obtained for NO3‐N‐content in April/May in the 0—60 cm soil layer and sugar yield (R2= 0.62—0.78). Maximum sugar yield was obtained with 220 kg N/ha soil nitrat content in April/May in 0—‐60 cm. A wide N‐optimum range for maximal sugar yield was observed. Deviations less than 50 kg N/ha from the optimal N amount caused no significant changes in sugar yield.Higher amounts of late available nitrogen deposited at greater soil depths caused a decrease in sugar content and an increase in alpha‐amino‐N and sodium. Early applications of nitrogen fertilizer (before sowing) are endangered to be leached to lower depths with heavy rain falls and therefore may cause detrimental effects on juice purity and sugar content. For obtaining maximal sugar yield it is recommended to apply N‐fertilizer 1 or 2 weeks after and not before seeding.Related to the wide optimum of N‐requirement ist seems possible to determine the use of Nitrogen fertilizer according to local experience. In special cases (slurry, tillage of wet soils, preceeding vegetables or legumes) it is suggested to determine NO3‐N‐content in April (0—60 cm) and to apply nitrogen fertilizer supplementary to 220 kg N/ha.