Plant and Soil

, Volume 112, Issue 2, pp 155–165 | Cite as

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

  • G. P. Warren
  • D. C. Whitehead


The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg−1 dry soil)=(Nmin×0.672)+(Ninc×0.840)+(Nmom×0.227)−5.12 was found to account for 91% of the variance in available soil N, where Nmin=mineral N, Ninc=N mineralized on incubation and Nmom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (Nao) the closest relationship with other soil characteristics was: Nao=[Ninc×(1.395−0.0347×C∶Nmom]+[Nmom×0.1416], where C∶Nmom=C∶N ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.

The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.

Key words

macro-organic matter nitrogen availability nitrogen fractionation soil nitrogen 


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Copyright information

© Kluwer Academic Publishers 1988

Authors and Affiliations

  • G. P. Warren
    • 1
  • D. C. Whitehead
    • 1
  1. 1.Institute for Grassland and Animal ProductionMaidenheadUK

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