Plant and Soil

, Volume 139, Issue 2, pp 253–263

Root-induced nitrogen mineralisation: A nitrogen balance model

  • Bryan Griffiths
  • David Robinson


The possibility is examined that carbon (C) released into the soil from a root could enhance the availability of nitrogen (N) to plants by stimulating microbial activity. Two models are described, both of which assume that C released from roots is used by bacteria to mineralise and immobilise soil organic N and that immobilised N released when bacteria are grazed by bacterial-feeding nematodes or protozoa is taken up by the plant. The first model simulates the individual transformations of C and N and indicates that root-induced N mineralisation could supply only up to 10% of the plant's requirement, even if unrealistically ideal conditions are assumed. The other model is based on evidence that about 40% of immobilised N is subsequently taken up by the plant. A small net gain of N by the plant is shown (i.e. the plant takes up more N than it loses through exudation), although with exudate of up to C:N 33:1 less than 6% of the plant's requirement is supplied by root-induced N mineralisation. It is argued, however, that rhizosphere bacteria do not use plant-derived C to mineralise soil organic N to any great extent and that in reality root-induced N mineralisation is even less important than these models indicate.

Key words

carbon exudation mineralisation nematode nitrogen protozoa rhizosphere root uptake 


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Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • Bryan Griffiths
    • 1
  • David Robinson
    • 1
  1. 1.Soil-Plant Dynamics Group, Cellular and Environmental Physiology DepartmentScottish Crop Research InstituteInvergowieUK

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