Nitrogen Uptake and Nitrogen Residuals of Winter Oil‐Seed 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 33dt/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.
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Aufhammer et al. (1994) studied this question.