Comparison of nitrogen mineralisation patterns of Cichorium intybus and Medicago sativa

Abstract

Little is known about the rate of mineralisation of chicory (Cichorium intybus) residues and how this may influence the availability of nitrogen (N) for subsequent crops. An incubation study was conducted to compare the relative rates of N mineralisation and carbon dioxide production from different plant fractions of chicory and lucerne (Medicago sativa) over 112 days. Plants were separated into leaves, stems, fibrous roots (<1 mm), and taproots (>4 mm), which were either ground or segmented, and then mixed with soil in sealed jars. Results showed that net N mineralisation occurred from day 7 for lucerne leaves, but not until day 56 for chicory leaves. By day 112, chicory leaves only produced approximately 25% of the N mineralised by lucerne leaves. Segmented chicory taproots released 32% and 24% more of the plant N and carbon (C), respectively, than any other chicory and lucerne plant fractions despite having a C:N ratio greater than 30. The presence of a common fungal saprophyte (Rhizopus spp.) in the segmented chicory taproot treatments appeared to accelerate the net N mineralisation rate. Whilst coarse chicory roots released mineral N relatively rapidly, the lower N content observed in the chicory plant residues limited the capacity of chicory to release the same quantity of mineral N compared to lucerne. Chicory needs to be grown with a companion legume so that N mineralisation of the residues better matches the demands of N requirement for the following non‐legume cropping phase.