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Turnover of grain legume N rhizodeposits and effect of rhizodeposition on the turnover of crop residues
Authors:Email author" target="_blank">Jochen?MayerEmail author  Franz?Buegger  Erik?Steen?Jensen  Michael?Schloter  Jürgen?He?
Institution:(1) Department of Organic Farming and Cropping, University of Kassel, Nordbahnhofstr. 1a, 37213 Witzenhausen, Germany;(2) GSF Research Centre for Environment and Health, Institute of Soil Ecology, P.O. Box 1129, 85758 Oberschleißheim, Germany;(3) Plant Research Department, PRD-301, Risø National Laboratory, 4000 Roskilde, Denmark;(4) Present address: Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstrasse 191, 8046 Zürich, Switzerland
Abstract:The turnover of N derived from rhizodeposition of faba bean (Vicia faba L.), pea (Pisum sativum L.) and white lupin (Lupinus albus L.) and the effects of the rhizodeposition on the subsequent C and N turnover of its crop residues were investigated in an incubation experiment (168 days, 15 °C). A sandy loam soil for the experiment was either stored at 6 °C or planted with the respective grain legume in pots. Legumes were in situ 15N stem labelled during growth and visible roots were removed at maturity. The remaining plant-derived N in soil was defined as N rhizodeposition. In the experiment the turnover of C and N was compared in soils with and without previous growth of three legumes and with and without incorporation of crop residues. After 168 days, 21% (lupin), 26% (faba bean) and 27% (pea) of rhizodeposition N was mineralised in the treatments without crop residues. A smaller amount of 15–17% was present as microbial biomass and between 30 and 55% of mineralised rhizodeposition N was present as microbial residue pool, which consists of microbial exoenzymes, mucous substances and dead microbial biomass. The effect of rhizodeposition on the C and N turnover of crop residues was inconsistent. Rhizodeposition increased the crop residue C mineralisation only in the lupin treatment; a similar pattern was found for microbial C, whereas the microbial N was increased by rhizodeposition in all treatments. The recovery of residual 15N in the microbial and mineral N pool was similar between the treatments containing only labelled crop residues and labelled crop residues + labelled rhizodeposits. This indicates a similar decomposability of both rhizodeposition N and crop residue N and may be attributable to an immobilisation of both N sources (rhizodeposits and crop residues) as microbial residues and a subsequent remineralisation mainly from this pool.Abbreviations C or Ndec C or N decomposed from residues - C or Nmic microbial C or N - C or Nmicres microbial residue C or N - C or Nmin mineralised C or N - C or Ninput added C or N as crop residues and/or rhizodeposits - dfr derived from residues - dfR derived from rhizodeposition - Ndfr N derived from residues - NdfR N derived from rhizodeposition - Nloss losses of N derived from residues - SOM soil organic matter - WHC water holding capacity
Keywords:15N  C and N mineralisation  Microbial residues  Microbial biomass  Residue turnover  Rhizodeposition
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