N-Freisetzung durch Ölrettich- und Weizenwurzeln unter Bodenbedingungen

Abstract

Knowledge about net-N release of living plant roots is of great importance for balance nitrogen in agrarian ecosystems and for calculation of N fertilization. In order to quantify this process spring wheat (Triticum aestivum) and oil radish (Raphanus sativus) were grown for six weeks in pots containing a 1: 1 (w/w) mixture of soil and quartz sand. ¹⁵N was applied three times to the shoots as ¹⁵NH₃ for three hours (100 ppm NH₃ with 95 at.-% ¹⁵N_exc). Seven days after the last labelling period (tillering stage of wheat) first plants were harvested. Second harvest took place 18 days after last labelling (shooting stage). Total N and ¹⁵N were measured in shoots, roots, and soil compartments using an elemental analyzer coupled with an emission spectrometer.

Both plant species assimilated 55 % of the ¹⁵N offered. After one weak approximately 80% of the ¹⁵N incorporated by the plants were found in the shoots, 11...12 % in the roots and 6...7 % had been released in the soil. Net N release of wheat roots increased up to the second harvest significantly (11 %) while root portion declined to 8 %. In contrast in the case of oilradish, N distribution was almost the same in both development stages, e. g. the N release seems to be in balance with re-incorporation in this time.