Effects of mustard residues on the carbon and nitrogen turnover in undisturbed soil microcosms

The C‐ and N‐turnover of undisturbed, irrigated 25 cm soil microcosms of a Typic Agrudalf from loess were followed during a laboratory incubation of about 200 days. Besides the untreated control columns two treatments were installed to test the effects of the application of white mustard (Sinapis alba L.) on both nutrient cycles (either mixing the dried plant residues to 0–8 cm or surface application). Each of the treatments is represented by 4 soil columns to account for soil variability. The C‐budget was mainly altered for soil respiration, which increased for the microcosms treated with mustard rapidly after application. After 4 weeks no differences could be proved however. The loss of soluble C‐compounds, which was unimportant for the budget, reflected no one of the treatments with mustard. Net N mineralization, as calculated from the NO₃‐leaching, could be well fitted by zero‐order kinetics. Although the high variability of the net N mineralization of the replicates mustard application significantly rises the N‐release. No difference could be proved for the different techniques of application however. In the mixed treatment 38% of the nitrogen added with the mustard was decomposed during the incubation period, in the surface treatment 34%.