NITROGEN UPTAKE AND NITROGEN RESIDUALS OF WINTER OILSEED RAPE AND FALLOUT RAPE

The objective of the investigation was a study of the relationship between seed dry-matter production and vegetative dry-matter production in oil-seed rape crops and their dependence on the production conditions. In addition to the relationship between the N-uptake during the vegetation period and the N-residue after harvest was of major interest. Furthermore the potential for N-uptake in fallout rape was measured. Over two vegetation periods factorial field experiments with winter oil-seed rape, cv. Lirabon, different drilling techniques and different nitrogen fertilization levels were tested. Measured traits were: the dry-matter accumulation including root mass and fall-off leaf-material mass, the N-uptake of both the oil-seed crops and the fallout rape stands, and, simultaneously, the soil NO3-N content. Finally the harvest indices and the N-harvest indices were calculated. Combined with a N-uptake of up to 330 kg N/ha, oil-seed rape crops produced up to 200 dt dry matter/ha. At seed yield levels of 33 dt/ha (d.m.), harvest indices varied from 0.14-0.23 and N-harvest indices varied from 0.30-0.50. As a result of the residue of vegetative plant material at harvest, leaf losses before harvest and the soil NO3-N-contents at harvest up to 275 kg N/ha remained in the field. After the harvest of oil-seed rape, the soil NO3-N-contents were quickly reduced by emerging and growing fallout rape stands. However, following soil-preparation measures in the autumn, a continuous rise in the soil NO3-N-content was observed.